diff --git a/TODO.org b/TODO.org
index 1b294a45..fed58224 100644
--- a/TODO.org
+++ b/TODO.org
@@ -315,10 +315,6 @@ keyword resolves against the expected type and against nothing else, so two enum
 could always share a member spelling. What the prefix buys is the call site read
 on its own.
 
-** NEXT The .fln printer writes a flat let where the scope does not matter
-Decided 2026-09-25: a let whose name no later statement of its block mentions prints
-flat, not as a nested block; a one-argument and/or prints as its argument.
-
 ** WAIT ML-style patterns
 Held 2026-09-25 as a future direction, like the JS backend: nested destructuring,
 guards, or-patterns, literals at any depth, exhaustiveness over the nesting.
diff --git a/bin/main.ml b/bin/main.ml
index 324fced9..0a6184cd 100644
--- a/bin/main.ml
+++ b/bin/main.ml
@@ -337,7 +337,8 @@ let () =
       if Flan.Source.is_indented path then
         print_string (Flan.Paren_printer.program ~source forms)
       else
-        match Flan.Indent_printer.program ~source forms with
+        let macros = Flan.Body_macros.table ~file:path forms in
+        match Flan.Indent_printer.program ~source ~macros forms with
         | text -> print_string text
         | exception Flan.Indent_printer.Unprintable (f, why) ->
           Flan.Loc.failk "convert/unprintable" f.Flan.Form.loc
diff --git a/lib/body_macros.ml b/lib/body_macros.ml
new file mode 100644
index 00000000..f03c0d9d
--- /dev/null
+++ b/lib/body_macros.ml
@@ -0,0 +1,196 @@
+(** What the indented printer needs to know of macros: which take a body run
+    in order and at which argument it starts, and which names their
+    expansions spell.
+
+    A body is read off the macro's definition. A macro whose rest parameter
+    is spliced, whole or from a fixed index on, only into places whose forms
+    run in order — a [do], the body of a [let], [fn], [when], [while] or
+    [loop], or the body of another such macro — takes a body there, provided
+    nothing else of it depends on how the body is split into arguments: out
+    of its templates the rest parameter may only be counted against the
+    body's start ([(< (length r) 1)]), read before the body ([(at r 0)] when
+    the body starts at 1), or have the body's first form tested with a
+    predicate ([(form-empty-list? (at r 0))]), since a [let] taking in the
+    forms after it changes how many there are and nothing about the first.
+    [comment] counts too: nothing in it runs. The printer lets a [let] in such
+    a body take in the statements after it, as it does in a [do].
+
+    The names a template spells outside its unquotes are what its expansion
+    can refer to without its call spelling them: a [let] of one of those
+    names is not given a longer scope over a call of that macro. *)
+
+type t = {
+  bodies : (string, int) Hashtbl.t;  (** called name -> argument the body starts at *)
+  names : (string, string list) Hashtbl.t;  (** called name -> names its templates spell *)
+}
+
+let create () = { bodies = Hashtbl.create 32; names = Hashtbl.create 64 }
+
+(* Core forms whose trailing arguments are a body run in order, and how many
+   arguments come before it. *)
+let core = [ ("do", 0); ("let", 1); ("fn", 1); ("when", 1); ("while", 1); ("loop", 1);
+             ("defer", 0); ("with-allocator", 1) ]
+
+let body_start (t : t) h =
+  match List.assoc_opt h core with Some k -> Some k | None -> Hashtbl.find_opt t.bodies h
+
+(* The names a template spells outside its unquotes. *)
+let rec template_names (f : Form.t) acc =
+  match f.v with
+  | Form.List ({ v = Form.Sym ("unquote" | "unquote-splicing"); _ } :: _) -> acc
+  | Form.Sym s -> s :: acc
+  | Form.List l | Form.Vec l | Form.Map l -> List.fold_left (fun a x -> template_names x a) acc l
+  | _ -> acc
+
+let rec templates (f : Form.t) acc =
+  match f.v with
+  | Form.List [ { v = Form.Sym "quasiquote"; _ }; x ] -> x :: acc
+  | Form.List l | Form.Vec l | Form.Map l -> List.fold_left (fun a x -> templates x a) acc l
+  | _ -> acc
+
+(* The argument index the body of [(defmacro name [p ... & r] body ...)]
+   starts at, or [None]. [known] gives another macro's. *)
+let body_of ~(known : string -> int option) name ps body : int option =
+  if name = "comment" then Some 0
+  else
+    let rec split fixed = function
+      | { Form.v = Form.Sym "&"; _ } :: [ { Form.v = Form.Sym r; _ } ] -> Some (fixed, r)
+      | { Form.v = Form.Sym "&"; _ } :: _ -> None
+      | _ :: rest -> split (fixed + 1) rest
+      | [] -> None
+    in
+    match split 0 ps with
+    | None -> None
+    | Some (fixed, r) ->
+      let is_r (f : Form.t) = f.v = Form.Sym r in
+      let rec mentions (f : Form.t) =
+        match f.v with
+        | Form.Sym s -> s = r
+        | Form.List l | Form.Vec l | Form.Map l -> List.exists mentions l
+        | _ -> false
+      in
+      let int (f : Form.t) = match f.v with Form.Int i -> Some (Int64.to_int i) | _ -> None in
+      let at_r (f : Form.t) =
+        match f.v with
+        | Form.List [ { v = Form.Sym "at"; _ }; x; i ] when is_r x -> int i
+        | _ -> None
+      in
+      let bodies = ref [] and reads = ref [] and bad = ref false in
+      (* Splices of [r] in a template, each where it lands. *)
+      let splice_from (e : Form.t) =
+        match e.v with
+        | Form.Sym s when s = r -> Some 0
+        | Form.List [ { v = Form.Sym "form-rest"; _ }; x; k ] when is_r x -> int k
+        | _ -> None
+      in
+      let lookup h = match List.assoc_opt h core with Some k -> Some k | None -> known h in
+      let rec template (f : Form.t) =
+        match f.v with
+        | Form.List [ { v = Form.Sym "unquote"; _ }; e ] ->
+          (match at_r e with
+           | Some i -> reads := i :: !reads
+           | None -> if mentions e then bad := true)
+        | Form.List [ { v = Form.Sym "unquote-splicing"; _ }; e ] ->
+          (* Anywhere but in a list's items: a vector, a map. *)
+          if mentions e then bad := true
+        | Form.List l ->
+          let head = match l with { v = Form.Sym h; _ } :: _ -> Some h | _ -> None in
+          (* A label after while, until or dotimes comes before the test. *)
+          let label =
+            match head, l with
+            | Some ("while" | "until" | "dotimes"), _ :: { v = Form.Kw _; _ } :: _ -> 1
+            | _ -> 0
+          in
+          List.iteri
+            (fun i (x : Form.t) ->
+               match x.v with
+               | Form.List [ { v = Form.Sym "unquote-splicing"; _ }; e ] ->
+                 (match splice_from e, Option.bind head lookup with
+                  | Some k, Some b when i >= b + 1 + label -> bodies := k :: !bodies
+                  | _ -> if mentions e then bad := true)
+               | _ -> template x)
+            l
+        | Form.Vec l | Form.Map l ->
+          List.iter
+            (fun (x : Form.t) ->
+               match x.v with
+               | Form.List [ { v = Form.Sym "unquote-splicing"; _ }; e ] ->
+                 if mentions e then bad := true
+               | _ -> template x)
+            l
+        | _ -> ()
+      in
+      (* The macro's own code, out of its templates: [r] only counted, read
+         before the body, or its first form tested. [k] is the body's start
+         within [r], known once the templates are read. *)
+      let rec code k (f : Form.t) =
+        match f.v with
+        | Form.List [ { v = Form.Sym "quasiquote"; _ }; x ] -> template x
+        | Form.Sym s when s = r -> bad := true
+        | Form.List [ { v = Form.Sym ("<" | ">=" | "=" | "<=" | ">"); _ }; a; b ] ->
+          (match a.v, b.v with
+           | Form.List [ { v = Form.Sym "length"; _ }; x ], _ when is_r x ->
+             (match int b with Some c when c <= k + 1 -> () | _ -> code k b; bad := true)
+           | _, Form.List [ { v = Form.Sym "length"; _ }; x ] when is_r x ->
+             (match int a with Some c when c <= k + 1 -> () | _ -> code k a; bad := true)
+           | _ -> code k a; code k b)
+        | Form.List [ { v = Form.Sym p; _ }; e ]
+          when String.length p > 1 && p.[String.length p - 1] = '?' && at_r e <> None ->
+          (match at_r e with Some i when i <= k -> () | _ -> bad := true)
+        | Form.List _ when at_r f <> None ->
+          (match at_r f with Some i when i < k -> () | _ -> bad := true)
+        | Form.List l | Form.Vec l | Form.Map l -> List.iter (code k) l
+        | _ -> ()
+      in
+      (* The templates first, for [k]; then the rest of the code against it. *)
+      List.iter (fun t -> template t) (List.fold_left (fun a x -> templates x a) [] body);
+      match !bodies with
+      | k :: more when (not !bad) && List.for_all (( = ) k) more
+                       && List.for_all (fun i -> i < k) !reads ->
+        List.iter (code k) body;
+        if !bad then None else Some (fixed + k)
+      | _ -> None
+
+let add (t : t) ~qualify forms =
+  let local = Hashtbl.create 8 in
+  List.iter
+    (fun (f : Form.t) ->
+       match f.v with
+       | Form.List ({ v = Form.Sym "defmacro"; _ } :: { v = Form.Sym name; _ }
+                    :: { v = Form.Vec ps; _ } :: body) ->
+         let known h =
+           match Hashtbl.find_opt local h with
+           | Some k -> Some k
+           | None -> Hashtbl.find_opt t.bodies h
+         in
+         Hashtbl.replace t.names (qualify name)
+           (List.fold_left (fun a x -> template_names x a) []
+              (List.fold_left (fun a x -> templates x a) [] body));
+         (match body_of ~known name ps body with
+          | Some k -> Hashtbl.replace local name k; Hashtbl.replace t.bodies (qualify name) k
+          (* A definition of the same name as a prelude macro replaces it. *)
+          | None -> Hashtbl.remove local name; Hashtbl.remove t.bodies (qualify name))
+       | _ -> ())
+    forms
+
+(** The prelude's macros, those of the packages [forms] imports (qualified
+    by their alias) and [forms]' own. An import that cannot be found or read
+    adds nothing. *)
+let table ?file (forms : Form.t list) : t =
+  let t = create () in
+  let prelude = try Reader.read_all ~file:Prelude.file Prelude.source with _ -> [] in
+  add t ~qualify:Fun.id prelude;
+  (match file with
+   | None -> ()
+   | Some file ->
+     List.iter
+       (fun (alias, path, loc) ->
+          try
+            let d = Load.resolve_dir ~file loc path in
+            let files = if Sys.is_directory d then Load.source_entries d else [ d ] in
+            let fs = List.concat_map Source.read_file files in
+            add t ~qualify:(fun n -> alias ^ "/" ^ n) fs
+          with _ -> ())
+       (Load.imports_of forms));
+  add t ~qualify:Fun.id forms;
+  t
diff --git a/lib/indent_printer.ml b/lib/indent_printer.ml
index 3b7b2512..844f2dda 100644
--- a/lib/indent_printer.ml
+++ b/lib/indent_printer.ml
@@ -69,6 +69,226 @@ let rec same (a : Form.t) (b : Form.t) =
 
 let is_sym s (f : Form.t) = match f.v with Form.Sym x -> x = s | _ -> false
 
+(* Inside a quasiquote the forms are a template, not code: an unquote may put
+   anything in place, a name a flat [let] would then capture included, so no
+   [let] there takes in what follows it and no one-argument [and] is dropped. *)
+let quasi = ref 0
+
+let in_quasi (f : Form.t) k =
+  match f.v with
+  | Form.List ({ v = Form.Sym "quasiquote"; _ } :: _) ->
+    incr quasi;
+    Fun.protect ~finally:(fun () -> decr quasi) k
+  | _ -> k ()
+
+(* ── Flat lets ─────────────────────────────────────────────────────── *)
+
+(* A [let] in the indented syntax is always flat: [let x = v] scopes to the
+   end of its block. So a [let] with statements after it in a body is printed
+   as the [let] taking those statements into its own body. That changes
+   nothing when none of them refers to a name it binds — a [let] is no frame
+   and a [defer] is function-scoped, so the longer scope releases nothing
+   later. When one does, the name is renamed inside the [let] to one the
+   whole top-level form does not use. Where a rename cannot be trusted, or
+   where the statements are not a body run in order, the [let] goes in a
+   [do:] block of its own instead. *)
+
+(* Macros whose trailing arguments are a body run in order, by the name they
+   are called by, and the argument the body starts at. Set by [program]. *)
+let macros : Body_macros.t ref = ref (Body_macros.create ())
+
+(* Every name spelled in the top-level form being printed, and every part of
+   a dotted or slashed one: a new name is none of them. *)
+let used : (string, unit) Hashtbl.t = Hashtbl.create 64
+
+let rec note_used (f : Form.t) =
+  match f.v with
+  | Form.Sym s ->
+    List.iter (fun p -> Hashtbl.replace used p ())
+      (s :: List.concat_map (String.split_on_char '/') (String.split_on_char '.' s))
+  | Form.List l | Form.Vec l | Form.Map l -> List.iter note_used l
+  | _ -> ()
+
+(* Each new name, and the name it was made from: renaming [x-3] again makes
+   [x-4], not [x-3-2]. *)
+let made : (string, string) Hashtbl.t = Hashtbl.create 16
+
+let fresh n =
+  let n = Option.value (Hashtbl.find_opt made n) ~default:n in
+  let rec go i =
+    let c = n ^ "-" ^ string_of_int i in
+    if Hashtbl.mem used c then go (i + 1)
+    else (Hashtbl.replace used c (); Hashtbl.replace made c n; c)
+  in
+  go 2
+
+let prefixed pre s =
+  String.length s > String.length pre && String.sub s 0 (String.length pre) = pre
+
+let dotted s = String.length s > 1 && s.[0] = '.'
+
+let all f l =
+  List.fold_right
+    (fun x acc -> match f x, acc with Some y, Some ys -> Some (y :: ys) | _ -> None)
+    l (Some [])
+
+(* A struct pattern's entries as [name .field] pairs, in order: [.x] is
+   [x .x], and [:keys [x y]] is [x .x y .y] ([Parse.dmap]). [None] for a
+   shape [Parse] refuses. *)
+let struct_pairs (items : Form.t list) =
+  let rec go = function
+    | [] -> Some []
+    | ({ Form.v = Form.Sym s; _ } as f) :: rest when dotted s ->
+      let n = String.sub s 1 (String.length s - 1) in
+      Option.map (fun r -> ({ f with v = Form.Sym n }, f) :: r) (go rest)
+    | { Form.v = Form.Kw "keys"; _ } :: { Form.v = Form.Vec ns; _ } :: rest ->
+      Option.bind
+        (all (fun (n : Form.t) -> match n.v with
+             | Form.Sym s -> Some (n, { n with v = Form.Sym ("." ^ s) })
+             | _ -> None) ns)
+        (fun ps -> Option.map (fun r -> ps @ r) (go rest))
+    | pat :: ({ Form.v = Form.Sym s; _ } as f) :: rest when dotted s ->
+      Option.map (fun r -> (pat, f) :: r) (go rest)
+    | _ -> None
+  in
+  go items
+
+(* The names a binding target binds, or [None] for a target [Parse] would
+   refuse. *)
+let rec pat_names (t : Form.t) : string list option =
+  match t.v with
+  | Form.Sym s -> Some [ s ]
+  | Form.Vec l ->
+    Option.map List.concat
+      (all (fun (x : Form.t) -> if x.v = Form.Sym "&" then Some [] else pat_names x) l)
+  | Form.Map l ->
+    Option.bind (struct_pairs l) (fun ps ->
+        Option.map List.concat (all (fun (p, _) -> pat_names p) ps))
+  | _ -> None
+
+let binds n t = match pat_names t with Some ns -> List.mem n ns | None -> false
+
+(* Whether [f] mentions [n]: the name, or a field path or qualified name
+   starting with it. Any occurrence counts, a quoted one or one under an
+   unquote included. A macro whose expansion names a variable its call does
+   not spell is [flatten]'s to see, through [!macros.names]; one defined
+   nowhere [Body_macros.table] reads is the case nothing here can see. *)
+let rec mentions n (f : Form.t) =
+  match f.v with
+  | Form.Sym s -> s = n || prefixed (n ^ ".") s || prefixed (n ^ "/") s
+  | Form.List l | Form.Vec l | Form.Map l -> List.exists (mentions n) l
+  | _ -> false
+
+(* [mentions], less what a [let] inside [f] rebinds before any use: a later
+   [let a = ...] of the same name is a new [a], not the one before it. *)
+let rec refers n (f : Form.t) =
+  match f.v with
+  | Form.List ({ v = Form.Sym "let"; _ } :: { v = Form.Vec bs; _ } :: body) ->
+    let rec go = function
+      | t :: v :: rest -> refers n v || ((not (binds n t)) && go rest)
+      | [ t ] -> refers n t
+      | [] -> List.exists (refers n) body
+    in
+    go bs
+  | Form.List l | Form.Vec l | Form.Map l -> List.exists (refers n) l
+  | _ -> mentions n f
+
+(* A binding target with [n] renamed [n']. A struct pattern that binds [n]
+   is written out as pairs, so the field keeps its name. *)
+let rec rename_pat n n' (t : Form.t) : Form.t option =
+  match t.v with
+  | Form.Sym s when s = n -> Some { t with v = Form.Sym n' }
+  | Form.Sym _ -> Some t
+  | Form.Vec l -> Option.map (fun l -> { t with v = Form.Vec l }) (all (rename_pat n n') l)
+  | Form.Map l ->
+    Option.bind (struct_pairs l) (fun ps ->
+        if not (binds n t) then Some t
+        else
+          Option.map
+            (fun ps -> { t with v = Form.Map (List.concat_map (fun (p, f) -> [ p; f ]) ps) })
+            (all (fun (p, f) -> Option.map (fun p -> (p, f)) (rename_pat n n' p)) ps))
+  | _ -> None
+
+(* [f] with [n] renamed [n'], or [None] where the rename cannot be trusted:
+   a quoted [n] is data, [n/x] names a package, and [(n ...)] may call a
+   function of that name rather than the local. A [let] inside renames its
+   targets as patterns. *)
+let rec rename n n' (f : Form.t) : Form.t option =
+  match f.v with
+  | Form.Sym s when s = n -> Some { f with v = Form.Sym n' }
+  | Form.Sym s when prefixed (n ^ ".") s ->
+    let k = String.length n in
+    Some { f with v = Form.Sym (n' ^ String.sub s k (String.length s - k)) }
+  | Form.Sym s when prefixed (n ^ "/") s -> None
+  | Form.List ({ v = Form.Sym ("quote" | "quasiquote"); _ } :: _) when mentions n f -> None
+  | Form.List ({ v = Form.Sym s; _ } :: _) when s = n -> None
+  | Form.List (({ v = Form.Sym "let"; _ } as h) :: ({ v = Form.Vec bs; _ } as bv) :: body) ->
+    let rec go = function
+      | t :: v :: rest ->
+        (match rename_pat n n' t, rename n n' v, go rest with
+         | Some t, Some v, Some r -> Some (t :: v :: r)
+         | _ -> None)
+      | rest -> all (rename n n') rest
+    in
+    (match go bs, all (rename n n') body with
+     | Some bs, Some body -> Some { f with v = Form.List (h :: { bv with v = Form.Vec bs } :: body) }
+     | _ -> None)
+  | Form.List l -> Option.map (fun l -> { f with v = Form.List l }) (all (rename n n') l)
+  | Form.Vec l -> Option.map (fun l -> { f with v = Form.Vec l }) (all (rename n n') l)
+  | Form.Map l -> Option.map (fun l -> { f with v = Form.Map l }) (all (rename n n') l)
+  | _ -> Some f
+
+(* [n] renamed [n'] in a [let]'s bindings [bs] and [body], from the binding
+   that binds it on: the values up to and including that binding's see the
+   outer [n]. *)
+let rename_let n n' (bs : Form.t list) (body : Form.t list) =
+  let rec go = function
+    | t :: v :: rest when binds n t ->
+      (* From here on, the rest reads as a [let] of its own. *)
+      (match rename_pat n n' t,
+             rename n n' { t with v = Form.List (Form.make (Form.Sym "let") t.loc
+                                                 :: Form.make (Form.Vec rest) t.loc :: body) } with
+       | Some t', Some { v = Form.List (_ :: { v = Form.Vec rest'; _ } :: body'); _ } ->
+         Some (t' :: v :: rest', body')
+       | _ -> None)
+    | t :: v :: rest -> Option.map (fun (r, b) -> (t :: v :: r, b)) (go rest)
+    | _ -> Some (bs, body)
+  in
+  go bs
+
+(* The [let] [f] taking [rest] in as the end of its body, its names that
+   [rest] refers to renamed; [None] when a rename cannot be trusted. *)
+let flatten (f : Form.t) (rest : Form.t list) =
+  match f.v with
+  | Form.List (({ v = Form.Sym "let"; _ } as h) :: ({ v = Form.Vec bs; _ } as bv) :: (_ :: _ as body))
+    when rest <> [] && bs <> [] && List.length bs mod 2 = 0 ->
+    Option.bind
+      (all pat_names (List.filteri (fun i _ -> i mod 2 = 0) bs))
+      (fun names ->
+         (* A call of a macro whose expansion names one of [ns]: that name
+            in the expansion means whatever is in scope where it lands, so
+            the let's scope may not newly reach it and a name it means may
+            not be renamed. *)
+         let rec captures ns (f : Form.t) =
+           match f.v with
+           | Form.List ({ v = Form.Sym m; _ } :: _)
+             when (match Hashtbl.find_opt !macros.names m with
+                 | Some ms -> List.exists (fun n -> List.mem n ms) ns
+                 | None -> false) -> true
+           | Form.List l | Form.Vec l | Form.Map l -> List.exists (captures ns) l
+           | _ -> false
+         in
+         let names = List.sort_uniq compare (List.concat names) in
+         let clash = List.filter (fun n -> List.exists (refers n) rest) names in
+         if List.exists (captures names) rest || List.exists (captures clash) body then None
+         else
+         List.fold_left
+           (fun acc n -> Option.bind acc (fun (bs, body) -> rename_let n (fresh n) bs body))
+           (Some (bs, body)) clash
+         |> Option.map (fun (bs, body) ->
+             { f with v = Form.List (h :: { bv with v = Form.Vec bs } :: (body @ rest)) }))
+  | _ -> None
+
 (* ── Expressions ───────────────────────────────────────────────────── *)
 
 (* Text and syntactic level, the same scale [Indent_reader] reads: 10 an atom
@@ -94,7 +314,7 @@ let rec expr (f : Form.t) : string * int =
   | Form.Vec xs -> ("[" ^ vec_text xs ^ "]", 10)
   | Form.Map xs -> ("{" ^ map_text xs ^ "}", 10)
   | Form.List [] -> ("()", 10)
-  | Form.List (h :: args) -> list f h args
+  | Form.List (h :: args) -> in_quasi f (fun () -> list f h args)
 
 and sym f s =
   if s = "==" then unprintable f "the name == (it reads as =)"
@@ -166,6 +386,8 @@ and list _f h args =
     if l >= 9 && t <> "" && R.is_neg_char t.[0] then ("-" ^ t, 8)
     else ("-(" ^ at 0 x ^ ")", 9)
   | Form.Sym "not", [ x ] -> ("not " ^ at 3 x, 3)
+  (* [and] or [or] of one value is that value. *)
+  | Form.Sym ("and" | "or"), [ x ] when !quasi = 0 -> expr x
   | Form.Sym "at", t :: (_ :: _ as idx) -> (at 9 t ^ "[" ^ commas idx ^ "]", 9)
   | Form.Sym s, [ t ]
     when String.length s > 1 && s.[0] = '.' && name_ok s
@@ -282,7 +504,7 @@ let stmts_of (f : Form.t) =
   | _ -> [ f ]
 
 (* Heads whose trailing arguments are a body, and how many come before it. *)
-let body_split (h : Form.t) args =
+let body_guess (h : Form.t) args =
   match h.v with
   | Form.Sym s ->
     let base =
@@ -326,21 +548,70 @@ let body_split (h : Form.t) args =
        else None)
   | _ -> None
 
+let let_sugar (f : Form.t) =
+  match f.v with
+  | Form.List ({ v = Form.Sym "let"; _ } :: { v = Form.Vec bs; _ } :: _ :: _) ->
+    (match pairs bs with None | Some [] -> false | Some _ -> true)
+  | _ -> false
+
+(* [Some (k, seq)]: the arguments from [k] on print as a block, and [seq]
+   when that block is a body run in order ([Body_macros]), whose start the
+   definition gives rather than the guess. *)
+let body_split (h : Form.t) args =
+  match body_guess h args, h.v with
+  | None, Form.Sym s ->
+    (* A body with a [let] in it is written as a block, where the [let] can
+       be flat. *)
+    (match Hashtbl.find_opt !macros.bodies s with
+     | Some b when List.exists let_sugar (List.filteri (fun i _ -> i >= b) args) ->
+       Some (b, true)
+     | _ ->
+       (* Any other call with a [let] among its arguments: the trailing run
+          of lists as a block, each [let] in a [do:] of its own, rather than
+          the [let] written as a call. *)
+       if List.exists let_sugar args then begin
+         let k = ref 0 in
+         List.iteri (fun i (a : Form.t) ->
+             match a.v with Form.List (_ :: _) -> () | _ -> k := i + 1) args;
+         if List.exists let_sugar (List.filteri (fun i _ -> i >= !k) args)
+         then Some (!k, false) else None
+       end
+       else None)
+  | None, _ -> None
+  | Some k, Form.Sym s ->
+    let n = List.length args in
+    (match List.assoc_opt s Body_macros.core, Hashtbl.find_opt !macros.bodies s with
+     | Some b, _ | None, Some b when b < n -> Some (b, true)
+     | _ -> Some (k, List.mem s [ "defmacro"; "defmethod" ]))
+  | Some k, _ -> Some (k, false)
+
 let sugar_heads =
   [ "let"; "set"; "if"; "when"; "cond"; "while"; "until"; "dotimes"; "match";
     "handler-case"; "handler-bind"; "restart-case"; "return"; "defer"; "do";
     "quasiquote"; "update" ]
 
-let rec block n (fs : Form.t list) : string list =
+
+(* [(do x)]: printed as [do:] and [x] as the one statement of its block. *)
+let in_do (x : Form.t) = { x with v = Form.List [ Form.make (Form.Sym "do") x.loc; x ] }
+
+(* [seq] when the block is a body run in order, where a [let] may take in
+   the statements after it. Not for the arguments of a call that happen to
+   print as a block, whose count that would change. *)
+let rec block ?(seq = true) n (fs : Form.t list) : string list =
   let rec go = function
     | [] -> []
-    | [ x ] -> stmt n ~last:true x
-    | x :: rest -> stmt n ~last:false x @ go rest
+    | [ x ] -> stmt n x
+    | x :: rest when let_sugar x ->
+      (match (if seq && !quasi = 0 then flatten x rest else None) with
+       | Some x' -> stmt n x'
+       | None -> stmt n (in_do x) @ go rest)
+    | x :: rest -> stmt n x @ go rest
   in
   go fs
 
-and stmt n ~last (f : Form.t) : string list =
-  let ls = match sugar n ~last f with Some ls -> ls | None -> plain n f in
+and stmt n (f : Form.t) : string list =
+  in_quasi f @@ fun () ->
+  let ls = match sugar n f with Some ls -> ls | None -> plain n f in
   (* The first line carries the line the form came from, for
      [Source_text.weave] to put the comments back by. *)
   match ls with
@@ -359,7 +630,7 @@ and plain n (f : Form.t) : string list =
   match f.v with
   | Form.List (h :: args) when args <> [] ->
     (match body_split h args with
-     | Some k when k < List.length args ->
+     | Some (k, seq) when k < List.length args ->
        let fixed = List.filteri (fun i _ -> i < k) args in
        let rest = List.filteri (fun i _ -> i >= k) args in
        let opener =
@@ -369,7 +640,7 @@ and plain n (f : Form.t) : string list =
          | Form.Sym s, [] when name_ok s && not (List.mem s reserved) -> s ^ ":"
          | _ -> head_text h ^ "(" ^ commas fixed ^ "):"
        in
-       [ ind n ^ guard opener ] @ block (n + 2) rest
+       [ ind n ^ guard opener ] @ block ~seq (n + 2) rest
      | _ when n + String.length text > width && fst (expr f) = text ->
        wrapped n "" f
      | _ -> one)
@@ -438,13 +709,13 @@ and label_of = function
   | ({ Form.v = Form.Kw k; _ }) :: rest when kw_ok k -> (":" ^ k ^ " ", rest)
   | rest -> ("", rest)
 
-and sugar n ~last (f : Form.t) : string list option =
+and sugar n (f : Form.t) : string list option =
   let i = ind n in
   match f.v with
   | Form.List ({ v = Form.Sym "let"; _ } :: { v = Form.Vec bs; _ } :: (_ :: _ as body)) ->
     (match pairs bs with
      | None | Some [] -> None
-     | Some prs -> Some (let_lines n ~last prs body))
+     | Some prs -> Some (let_lines n prs body))
   | Form.List [ { v = Form.Sym "update"; _ }; t; { v = Form.Sym ("+" | "-" | "*" | "/"); _ }; _ ]
     when not (R.simple_place t) ->
     Some [ i ^ guard (inline_text f) ]
@@ -590,7 +861,9 @@ and sugar n ~last (f : Form.t) : string list option =
        (match body with
         | [] -> Some [ head ]
         | [ x ] when (match x.v with
-            | Form.List ({ v = Form.Sym h; _ } :: _) -> not (List.mem h sugar_heads)
+            | Form.List (({ v = Form.Sym h; _ } as hf) :: args) ->
+              (* A call that takes a block is a statement, not a value. *)
+              not (List.mem h sugar_heads) && body_split hf args = None
             | _ -> true)
                   && String.length head + 3 + String.length (at 0 x) <= width
                   && not (!inside f) ->
@@ -675,10 +948,9 @@ and handler_clauses n cls =
   let cs = List.map clause cls in
   if List.mem None cs then None else Some (List.concat_map Option.get cs)
 
-(* A [let] last in its block reads to the block's end, so it is written flat.
-   One with siblings after it takes its body as an indented block under the
-   first binding, and the rest of the bindings go inside that block. *)
-and let_lines n ~last prs body =
+(* A [let] is always written flat: [block] has made it the last statement of
+   its block, so its body is the rest of the block. *)
+and let_lines n prs body =
   (* [(let [x (the T v)])] is [let x: T = v]. *)
   let bind ((t : Form.t), (v : Form.t)) =
     match t.v, v.v with
@@ -693,18 +965,13 @@ and let_lines n ~last prs body =
     | [] -> []
   in
   let lines n b = let p, v = bind b in tagged b (value_lines n p v) in
-  if last then List.concat_map (lines n) prs @ block n body
-  else
-    match prs with
-    | b :: rest ->
-      let p, v = bind b in
-      tagged b [ ind n ^ p ^ " = " ^ at 0 v ]
-      @ List.concat_map (lines (n + 2)) rest
-      @ block (n + 2) body
-    | [] -> block n body
+  List.concat_map (lines n) prs @ block n body
 
-(** A whole file: top-level forms with a blank line between them. *)
-let program ?source (fs : Form.t list) : string =
+(** A whole file: top-level forms with a blank line between them. [macros]
+    is [Body_macros.table] of the file; without it, the prelude's and the
+    file's own macros are known and no imported package's. *)
+let program ?source ?macros:m (fs : Form.t list) : string =
+  macros := (match m with Some m -> m | None -> Body_macros.table fs);
   spelling :=
     (match source with Some src -> Source_text.spelling src | None -> fun _ -> None);
   let cs = match source with Some src -> Source_text.comments src | None -> [] in
@@ -714,10 +981,18 @@ let program ?source (fs : Form.t list) : string =
          (fun (c : Source_text.comment) ->
             f.loc.Loc.line <= c.line && c.line < f.loc.Loc.eline)
          cs);
+  (* A flat [let] at the top level would take in the forms after it, so one
+     that is not last goes in a [do:] block. *)
+  let top x =
+    Hashtbl.reset used;
+    Hashtbl.reset made;
+    note_used x;
+    String.concat "\n" (stmt 0 x)
+  in
   let rec go = function
     | [] -> []
-    | [ x ] -> [ String.concat "\n" (stmt 0 ~last:true x) ]
-    | x :: rest -> String.concat "\n" (stmt 0 ~last:false x) :: go rest
+    | [ x ] -> [ top x ]
+    | x :: rest -> top (if let_sugar x then in_do x else x) :: go rest
   in
   let text =
     try String.concat "\n\n" (go fs) ^ "\n"
diff --git a/lib/indent_reader.ml b/lib/indent_reader.ml
index fd719c39..13d6b434 100644
--- a/lib/indent_reader.ml
+++ b/lib/indent_reader.ml
@@ -1118,10 +1118,13 @@ and let_stmt (s : st) : Form.t list =
       make (target :: v :: bs) body
     | _ -> make [ target; v ] body
   in
-  if (peek p).tok = INDENT then begin
-    let f = merged (block s ~after:"let") in
-    f :: stmts s
-  end
+  (* A let has no block: its name lasts to the end of the block it is in. *)
+  if (peek p).tok = INDENT then
+    failk "let-block" (peek_at p 1).loc
+      "this line is indented under let %s, which takes no block. A let's \
+       name lasts to the end of the block the let is in, so the lines after \
+       it go at the let's column"
+      (text_of target)
   else [ merged (stmts s) ]
 
 and stmt (s : st) : Form.t =
diff --git a/spec-syntax.md b/spec-syntax.md
index 38c8e9b6..5f05b1ef 100644
--- a/spec-syntax.md
+++ b/spec-syntax.md
@@ -176,8 +176,24 @@ Each item: the proposal, then the reason in one line.
 
 - **`let x = v`** scopes to the end of its block and reads as
   `(let [x v] rest…)`. Consecutive `let`s merge into one binding vector.
-  `let x = v` followed by a deeper-indented block scopes to that block only,
-  which is how the printer writes a `let` that has siblings after it.
+  A `let` is always flat: a line indented deeper under `let x = v` is
+  refused. To end a `let`'s scope early, put it in a `do:` block.
+  The printer writes every `let` flat. A `let` with statements after it
+  takes them into its body; when one of them means an outer name the `let`
+  rebinds, the `let`'s is renamed (`x` to `x-2`, a name the top-level form
+  does not use; a struct pattern is written as `{x-2 .x}` pairs). A macro's
+  body counts as statements run in order when its definition splices its
+  rest parameter only into a `do`, a `let`/`fn`/`when`/`while`/`loop` body or
+  another such macro's body; `comment` counts too. Where a rename cannot be
+  trusted (the name quoted, qualified as `x/y`, or called as `x(...)`), and
+  at the top level, among a call's other arguments and in a quasiquote, the
+  `let` goes in a `do:` block instead, and so does one whose longer scope
+  would reach a call of a macro whose template names the `let`'s name. A
+  macro's body counts only if nothing but its templates depends on how the
+  body splits into arguments (a count against the body's start, a predicate
+  on its first form). One case this cannot see: a macro defined nowhere the
+  printer reads (not the prelude, the file or an imported package) whose
+  expansion names a variable its call does not spell.
   Destructuring: `let {.x .y} = p`, `let [head & tail] = xs`. (`defer` is
   function-scoped, not let-scoped, `TODO.org` "defer may be written in a let",
   so merging never moves a cleanup.) **Built**; `let x =` with the value as an
@@ -344,8 +360,14 @@ Each step lands on its own, with `dune test --root .` green.
 3. **The printer**, `Form.t` → indented text, and a `flan convert` command.
    **Test:** for every corpus file, read with parens, print indented, read
    indented; the forms must be equal to the first read, after one normalisation:
-   a `let` whose whole body is another `let` counts as equal to the merged
-   `let`. That covers 394 files and runs on readers alone, so it's fast.
+   every name a `let` binds is renamed through its scope to one numbered by
+   binding order; then, in a body run in order, a `let` counts as equal to
+   itself taking in the later statements of the body (a macro's body by the
+   same rule as the printer's); `(do x)` with `x` a
+   `let` counts as `x`; a `let` whose whole body is another `let` counts as
+   equal to the merged `let`; `(and x)` and `(or x)` count as `x`. Taking in
+   and the one-argument `and` stop at a quote or quasiquote. That covers 394
+   files and runs on readers alone, so it's fast.
 4. **The dev loop.** Code-carrying wire ops (`eval`, `eval-expr`,
    `macroexpand`, `set`) get an explicit `:syntax` field instead of guessing
    from `:file`. The `:file` guess breaks for `<repl>`/`<inspect>` origins and
diff --git a/test/syntax/algorithms.fln b/test/syntax/algorithms.fln
index eaaa4d7a..151f6193 100644
--- a/test/syntax/algorithms.fln
+++ b/test/syntax/algorithms.fln
@@ -29,12 +29,12 @@ fn insertion-sort(coll: [$t]) -> () where ordered?($t)
   let length = length(coll)
   while and(i < length)
     let j = i
-      while j > 0
-            and coll[j] < coll[dec(j)]
-        let temp = coll[j]
-          coll[j] = coll[dec(j)]
-          coll[dec(j)] = temp
-        --(j)
+    while j > 0
+          and coll[j] < coll[dec(j)]
+      let temp = coll[j]
+      coll[j] = coll[dec(j)]
+      coll[dec(j)] = temp
+      --(j)
     ++(i)
 
 fn main() -> i32 = 0
@@ -43,10 +43,10 @@ comment():
   insertion-sort([\I \N \S \E \R \T \I \O \N \S \O \R \T])
   insertion-sort(slice([6 2 4 9 1 9 4 5], 0, 8))
   let str = bytes("INSERTIONSORT")
-    insertion-sort(str)
-    println(str)
+  insertion-sort(str)
+  println(str)
   let str = bytes("SELECTIONSORT")
-    selection-sort(str)
-    println(str)
+  selection-sort(str)
+  println(str)
   find-match("aababba", "abba")
   :-
diff --git a/test/syntax/flat/capture.flan b/test/syntax/flat/capture.flan
new file mode 100644
index 00000000..99916cf7
--- /dev/null
+++ b/test/syntax/flat/capture.flan
@@ -0,0 +1,6 @@
+(defmacro show-it [] `(println it))
+(defn main [] i32
+  (let [it 1]
+    (let [it 2] (show-it))
+    (show-it))
+  0)
diff --git a/test/syntax/flat/macros.flan b/test/syntax/flat/macros.flan
new file mode 100644
index 00000000..c76b1965
--- /dev/null
+++ b/test/syntax/flat/macros.flan
@@ -0,0 +1,46 @@
+;; Macro bodies the .fln printer must classify from their definitions:
+;; test_syntax converts this file, runs both and wants the same output.
+
+;; Counts its body forms: a let taking in the form after it would change the
+;; count, so the body is not one a let may be flattened in.
+(defmacro counted [& body]
+  (let [two (= (length body) 2)]
+    `(do (println ~(if two (Form.Sym {.s "true"}) (Form.Sym {.s "false"}))) ~@body)))
+
+;; Replaces the prelude's unless, and counts too.
+(defmacro unless [& args]
+  (let [two (= (length args) 3)]
+    `(do (println ~(if two (Form.Sym {.s "true"}) (Form.Sym {.s "false"}))) ~@(form-rest args 1))))
+
+;; The body once in a do and once as a vector's elements.
+(defmacro vtwice [& body]
+  `(do ~@body (println (length [~@body]))))
+
+;; The first body form is the loop's test.
+(defmacro labelled [& body]
+  `(while :l ~@body))
+
+;; A guard that only asks whether there is a body: a body run in order.
+(defmacro guarded [& args]
+  (if (< (length args) 1)
+    `(do)
+    `(do ~@args)))
+
+(defn main [] i32
+  (counted
+    (let [x 1] (println x))
+    (println 2))
+  (unless false
+    (let [y 3] (println y))
+    (println 4))
+  (vtwice
+    (let [z 5] (println z) z)
+    6)
+  (labelled
+    (let [go false] go)
+    (println 9))
+  (let [g 0]
+    (guarded
+      (let [g 1] (println g))
+      (println g)))
+  0)
diff --git a/test/syntax/flat/shadows.flan b/test/syntax/flat/shadows.flan
new file mode 100644
index 00000000..87dd7fa0
--- /dev/null
+++ b/test/syntax/flat/shadows.flan
@@ -0,0 +1,85 @@
+(defstruct P [x i32 y i32])
+(defn app [g (Fn [i32] i32) v i32] i32 (g v))
+
+(defn shadow-chain [] ()
+  (let [x 1]
+    (let [x (+ x 10)]
+      (println x))
+    (println x)
+    (let [x (+ x 100)]
+      (println x)
+      (let [x (* x 2)] (println x))
+      (println x))
+    (println x)))
+
+(defn closes [] i32
+  (let [x 1]
+    (let [x 5]
+      (println x))
+    (let [f 0]
+      (app (fn [y] (+ x y)) (+ f 2)))))
+
+(defn loopy [] ()
+  (let [i 0]
+    (while (< i 5)
+      (let [i (* i 100)]
+        (println i))
+      (set i (+ i 1))
+      (when (= i 3) (continue))
+      (println i))))
+
+(defn loopr [] i32
+  (loop [n 0 acc 0]
+    (let [n (* n 2)]
+      (println n))
+    (if (< n 4) (recur (+ n 1) (+ acc n)) acc)))
+
+(defn ret [a i32] i32
+  (let [a (+ a 1)]
+    (println a))
+  (when (> a 3)
+    (let [a 0] (println a))
+    (return a))
+  (let [a (- a 1)] (println a))
+  a)
+
+(defn deferring [] ()
+  (let [x 1]
+    (let [x 2]
+      (defer (println x)))
+    (defer (println x))
+    (println "body")))
+
+(defn destr [] ()
+  (let [p (P {.x 3 .y 4}) x 100]
+    (let [{.x .y} p]
+      (println (+ x y)))
+    (println x)
+    (let [{:keys [x]} p]
+      (println x))
+    (println x)
+    (let [[a b] [x 7]]
+      (println a))
+    (println x)))
+
+(defn dos [c bool] i32
+  (let [v 0]
+    (if c
+      (do (let [v 5] (println v)) (println v))
+      (do (let [v 6] (println v)) (println v)))
+    (unless c (let [v 9] (println v)) (println v))
+    (when c (let [v 8] (println v)) (println v))
+    v))
+
+(defn main [] i32
+  (shadow-chain)
+  (println (closes))
+  (loopy)
+  (println (loopr))
+  (println (ret 5))
+  (println (ret 1))
+  (deferring)
+  (destr)
+  (println (dos true))
+  (println (dos false))
+  0)
diff --git a/test/syntax/sand.fln b/test/syntax/sand.fln
index 1efab947..00c5bd9c 100644
--- a/test/syntax/sand.fln
+++ b/test/syntax/sand.fln
@@ -59,20 +59,20 @@ fn settle(row: i32, col: i32) -> ()
       velocity[row, col] = 0.0
       return
     let left? = col > 0 and 0 == grid[y, col - 1]
-      let right? = col < cols - 1 and 0 == grid[y, col + 1]
-      if left? or right?
-        let side =
-          if not left?
-            1
-          elif not right?
-            -1
-          else
-            if f32(rand()) < 0.5 then 1 else -1
-        grid[y, col + side] = grid[row, col]
-        grid[row, col] = 0
-        velocity[y, col + side] = vel
-        velocity[row, col] = 0.0
-        return
+    let right? = col < cols - 1 and 0 == grid[y, col + 1]
+    if left? or right?
+      let side =
+        if not left?
+          1
+        elif not right?
+          -1
+        else
+          if f32(rand()) < 0.5 then 1 else -1
+      grid[y, col + side] = grid[row, col]
+      grid[row, col] = 0
+      velocity[y, col + side] = vel
+      velocity[row, col] = 0.0
+      return
     y = y - 1
   velocity[row, col] = 0.0
 
diff --git a/test/test_syntax.ml b/test/test_syntax.ml
index 1da1c3c6..611a2161 100644
--- a/test/test_syntax.ml
+++ b/test/test_syntax.ml
@@ -3,7 +3,7 @@
 
    Four parts. Two programs hand-converted from paren to indented must read to
    the same forms. Every corpus file must survive paren -> printed indented ->
-   read indented unchanged, up to the one merge the spec allows. A table pins
+   read indented unchanged, up to the normalisation the spec allows. A table pins
    the lexical edge cases and the refusals, with their kinds. And a program in
    each syntax importing a package in the other builds and runs the same on
    both backends. *)
@@ -49,23 +49,178 @@ let describe_diff a b =
         (Form.to_string w) w.loc.Loc.line w.loc.Loc.col
     | None -> "equal"
 
-(* A [let] whose whole body is another [let] is the merged [let]: spec §4
-   step 3's one normalisation. Flan's [let] binds in order, so the two mean
-   the same thing. *)
-let rec norm (f : Form.t) : Form.t =
-  let v =
-    match f.v with
-    | Form.List (({ v = Form.Sym "let"; _ } as h) :: { v = Form.Vec bs; loc } :: body) ->
-      (match List.map norm body with
-       | [ { v = Form.List ({ v = Form.Sym "let"; _ } :: { v = Form.Vec bs2; _ } :: body2); _ } ] ->
-         Form.List (h :: Form.make (Form.Vec (List.map norm bs @ bs2)) loc :: body2)
-       | body -> Form.List (h :: Form.make (Form.Vec (List.map norm bs)) loc :: body))
-    | Form.List l -> Form.List (List.map norm l)
-    | Form.Vec l -> Form.Vec (List.map norm l)
-    | Form.Map l -> Form.Map (List.map norm l)
-    | v -> v
+(* Spec §4 step 3's normalisation. Each rule keeps the meaning.
+
+   First every name a [let] binds is renamed, through its scope, to one
+   numbered in the order the binders come: so two forms that differ only in
+   what their [let]s call things compare equal, and one where a name was
+   captured does not. Then, where statements are a body run in order, a
+   [let] takes in the statements after it (the printer's flat [let]; with
+   every [let] name unique by now, nothing after it can mean one of them). A
+   [(do x)] whose [x] is a [let] is [x], a [let] whose whole body is another
+   [let] is the merged [let], and [(and x)] and [(or x)] are [x]. The flat
+   [let] and the one-argument [and] stop at a quote or quasiquote: data, or
+   a template whose unquotes could name anything. *)
+
+(* A binding target with every struct pattern written as [name .field]
+   pairs: [{.x}] and [{:keys [x]}] are [{x .x}] (Parse.dmap). *)
+let rec pairs_pat (t : Form.t) : Form.t =
+  let dotted s = String.length s > 1 && s.[0] = '.' in
+  let rec items = function
+    | ({ Form.v = Form.Sym s; _ } as f) :: rest when dotted s ->
+      { f with v = Form.Sym (String.sub s 1 (String.length s - 1)) } :: f :: items rest
+    | { Form.v = Form.Kw "keys"; _ } :: { Form.v = Form.Vec ns; _ } :: rest ->
+      List.concat_map
+        (fun (n : Form.t) -> match n.v with
+           | Form.Sym x -> [ n; { n with v = Form.Sym ("." ^ x) } ]
+           | _ -> [ n ])
+        ns
+      @ items rest
+    | pat :: f :: rest -> pairs_pat pat :: f :: items rest
+    | rest -> rest
   in
-  { f with v }
+  match t.v with
+  | Form.Vec l -> { t with v = Form.Vec (List.map pairs_pat l) }
+  | Form.Map l -> { t with v = Form.Map (items l) }
+  | _ -> t
+
+(* The names a target so written binds, in order. *)
+let rec binders (t : Form.t) =
+  match t.v with
+  | Form.Sym "&" -> []
+  | Form.Sym s -> [ s ]
+  | Form.Vec l -> List.concat_map binders l
+  | Form.Map l -> List.concat (List.filteri (fun i _ -> i mod 2 = 0) (List.map binders l))
+  | _ -> []
+
+let canon (f : Form.t) : Form.t =
+  let k = ref 0 in
+  let look env s =
+    match List.assoc_opt s env with
+    | Some c -> c
+    | None ->
+      (* [x.y], a field path on a bound [x]. *)
+      match String.index_opt s '.' with
+      | Some i when i > 0 ->
+        (match List.assoc_opt (String.sub s 0 i) env with
+         | Some c -> c ^ String.sub s i (String.length s - i)
+         | None -> s)
+      | _ -> s
+  in
+  let rec go env (f : Form.t) =
+    let v =
+      match f.v with
+      | Form.Sym s -> Form.Sym (look env s)
+      (* Quoted data keeps its names: renaming them would hide a printer
+         that renamed them too. *)
+      | Form.List ({ v = Form.Sym ("quote" | "quasiquote"); _ } :: _) -> f.v
+      | Form.List (({ v = Form.Sym "let"; _ } as h) :: ({ v = Form.Vec bs; _ } as bv) :: body) ->
+        let rec binds env acc = function
+          | t :: v :: rest ->
+            let v' = go env v in
+            let t = pairs_pat t in
+            let env' =
+              List.fold_left (fun e n -> incr k; (n, "%" ^ string_of_int !k) :: e)
+                env (binders t)
+            in
+            binds env' (v' :: go env' t :: acc) rest
+          | rest -> (env, List.rev_append acc (List.map (go env) rest))
+        in
+        let env', bs' = binds env [] bs in
+        Form.List (h :: { bv with v = Form.Vec bs' } :: List.map (go env') body)
+      | Form.List l -> Form.List (List.map (go env) l)
+      | Form.Vec l -> Form.Vec (List.map (go env) l)
+      | Form.Map l -> Form.Map (List.map (go env) l)
+      | v -> v
+    in
+    { f with v }
+  in
+  go [] f
+
+(* The macros of the file being compared ([Body_macros.table]). *)
+let macros : Body_macros.t ref = ref (Body_macros.create ())
+
+(* Where the statements of a body start, for a head whose trailing arguments
+   are a body run in order. *)
+let body_start (l : Form.t list) =
+  let label k = match List.nth_opt l 1 with
+    | Some { Form.v = Form.Kw _; _ } -> k + 1 | _ -> k in
+  match l with
+  | { Form.v = Form.Sym h; _ } :: _ ->
+    (match h with
+     | "do" | "defer" -> Some 1
+     | "let" | "when" | "fn" | "loop" -> Some 2
+     | "while" | "until" | "dotimes" -> Some (label 2)
+     | "defmacro" -> Some 3
+     | "defmethod" -> Some 4
+     | "defn" | "defn-" ->
+       Some (match List.nth_opt l 4 with
+           | Some { Form.v = Form.Map _; _ } -> 5 | _ -> 4)
+     | h ->
+       (match List.assoc_opt h Body_macros.core with
+        | Some k -> Some (k + 1)
+        | None -> Option.map (fun k -> k + 1) (Hashtbl.find_opt !macros.bodies h)))
+  | _ -> None
+
+let is_let (f : Form.t) =
+  match f.v with Form.List ({ v = Form.Sym "let"; _ } :: _) -> true | _ -> false
+
+let rec shape ?(q = false) (f : Form.t) : Form.t =
+  let q = q || (match f.v with
+      | Form.List ({ v = Form.Sym ("quote" | "quasiquote"); _ } :: _) -> true | _ -> false) in
+  let sh = shape ~q in
+  (* A body's statements, each [let] taking in the ones after it. *)
+  let rec stmts = function
+    | [] -> []
+    | x :: (_ :: _ as rest) when not q ->
+      (match (sh x).v with
+       | Form.List (({ v = Form.Sym "let"; _ } as h) :: ({ v = Form.Vec (_ :: _); _ } as bv)
+                    :: (_ :: _ as body)) ->
+         [ sh { x with v = Form.List (h :: bv :: (body @ rest)) } ]
+       | _ -> sh x :: stmts rest)
+    | x :: rest -> sh x :: stmts rest
+  in
+  let seq_list l =
+    match body_start l with
+    | Some k when List.length l > k ->
+      List.map sh (List.filteri (fun i _ -> i < k) l)
+      @ stmts (List.filteri (fun i _ -> i >= k) l)
+    | _ -> List.map sh l
+  in
+  (* Handler and restart clauses: [(name [v] body ...)]. *)
+  let clause (c : Form.t) =
+    match c.v with
+    | Form.List (n :: p :: body) -> { c with v = Form.List (sh n :: sh p :: stmts body) }
+    | _ -> sh c
+  in
+  match f.v with
+  | Form.List [ { v = Form.Sym ("and" | "or"); _ }; x ] when not q -> sh x
+  | _ ->
+    let v =
+      match f.v with
+      | Form.List (({ v = Form.Sym "let"; _ } as h) :: { v = Form.Vec bs; loc } :: body) ->
+        (match stmts body with
+         | [ { v = Form.List ({ v = Form.Sym "let"; _ } :: { v = Form.Vec bs2; _ } :: body2); _ } ] ->
+           Form.List (h :: Form.make (Form.Vec (List.map sh bs @ bs2)) loc :: body2)
+         | body -> Form.List (h :: Form.make (Form.Vec (List.map sh bs)) loc :: body))
+      | Form.List (({ v = Form.Sym "handler-case"; _ } as h) :: body :: ({ v = Form.Vec cls; _ } as cv) :: more) ->
+        Form.List (h :: sh body :: { cv with v = Form.Vec (List.map clause cls) }
+                   :: List.map sh more)
+      | Form.List (({ v = Form.Sym "handler-bind"; _ } as h) :: ({ v = Form.Vec cls; _ } as cv) :: body) ->
+        Form.List (h :: { cv with v = Form.Vec (List.map clause cls) } :: stmts body)
+      | Form.List (({ v = Form.Sym "restart-case"; _ } as h) :: body :: cls) ->
+        Form.List (h :: sh body :: List.map clause cls)
+      | Form.List l ->
+        (match seq_list l with
+         | [ { v = Form.Sym "do"; _ }; x ] when is_let x -> x.v
+         | l -> Form.List l)
+      | Form.Vec l -> Form.Vec (List.map sh l)
+      | Form.Map l -> Form.Map (List.map sh l)
+      | v -> v
+    in
+    { f with v }
+
+let norm f = shape (canon f)
 
 let diag_text = function
   | Loc.Error d -> Printf.sprintf "%s %d:%d %s" d.Loc.kind d.dloc.Loc.line d.dloc.Loc.col d.dmsg
@@ -76,6 +231,10 @@ let diag_text = function
 let pair flan fln =
   match Reader.read_file flan, Source.read_file fln with
   | a, b ->
+    macros := Body_macros.table ~file:flan a;
+    (* Normalised: a hand conversion writes a let flat where its scope does
+       not matter, as the printer does. *)
+    let a = List.map norm a and b = List.map norm b in
     if not (same_forms a b) then
       fail "%s and %s read differently: %s" flan fln (describe_diff a b)
   | exception e -> fail "%s / %s: %s" flan fln (diag_text e)
@@ -112,13 +271,15 @@ let starts_of (fs : Form.t list) =
   let rec walk (f : Form.t) =
     (* Outermost first among forms starting at one place: [x = v] and its
        [x] start together, and the statement is what a comment is about. *)
-    let t = Form.to_string (norm f) in
+    let t = Form.to_string f in
     out := ((f.loc.Loc.line, f.loc.Loc.col, - String.length t), t) :: !out;
     match f.v with
     | Form.List l | Form.Vec l | Form.Map l -> List.iter walk l
     | _ -> ()
   in
-  List.iter walk fs;
+  (* The normalised forms: a [let] a flat line extended is, on both sides,
+     the one that holds what now follows it. *)
+  List.iter walk (List.map norm fs);
   List.map (fun ((l, c, _), t) -> (l, c, t)) (List.sort compare !out)
 
 let attachments src forms =
@@ -210,7 +371,8 @@ let () =
        | exception Loc.Error _ -> ()   (* not a program the paren reader takes *)
        | forms ->
          let source = In_channel.with_open_bin path In_channel.input_all in
-         match Indent_printer.program ~source forms with
+         macros := Body_macros.table ~file:path forms;
+         match Indent_printer.program ~source ~macros:!macros forms with
          | exception Indent_printer.Unprintable (f, why) ->
            fail "round trip %s: %s at %d:%d" path why f.loc.Loc.line f.loc.Loc.col
          | text ->
@@ -355,7 +517,8 @@ let () =
   (* Statements. *)
   reads "lets merge" "fn f() -> i32\n  let a = 1\n  let b = 2\n  a + b"
     "(defn f [] i32 (let [a 1 b 2] (+ a b)))";
-  reads "let with a block" "let a = 1\n  a\nb" "(let [a 1] a)\nb";
+  refuses "let with a block" "let a = 1\n  a\nb" "indent/let-block" "go at the let's column";
+  reads "flat let" "let a = 1\na\nb" "(let [a 1] a b)";
   reads "elif" "if a\n  1\nelif b\n  2\nelse\n  3" "(cond a 1 b 2 :else 3)";
   reads "one-line if" "x = if a then 1 else 2" "(set x (if a 1 2))";
   reads "assignment ops" "a[i] += 1" "(set (at a i) (+ (at a i) 1))";
@@ -417,6 +580,8 @@ let () =
   reads "one-line quote" "defmacro(m, [x]):\n  quote ~x + 1"
     "(defmacro m [x] (quasiquote (+ (unquote x) 1)))";
   reads "typed let" "let x: i32 = 5\nx" "(let [x (the i32 5)] x)";
+  refuses "a let takes no block" "fn f() -> ()\n  let x = 1\n    g(x)\n  h(x)"
+    "indent/let-block" "go at the let's column";
   (* And back: the printer writes the idioms. *)
   let prints name src want =
     match Reader.read_all ~file:"<p>" src with
@@ -436,6 +601,101 @@ let () =
   prints "a statement argument makes a block" "(foo 1 (set x 2))" "foo(1):\n  x = 2";
   prints "no arguments before the block" "(comment (f))" "comment:\n  f()";
   prints "typed let" "(defn f [] i32 (let [x (the i32 5)] x))" "let x: i32 = 5";
+  (* A let is always flat: it takes in the rest of its block. *)
+  prints "flat let" "(defn f [] () (let [j 1] (g j)) (h))" "  let j = 1\n  g(j)\n  h()";
+  prints "a chain of lets, all flat" "(defn f [] () (let [a 1] (let [b 2] (g b)) (k a)) (h))"
+    "  let a = 1\n  let b = 2\n  g(b)\n  k(a)\n  h()";
+  (* A later statement that means an outer name of the same spelling: the
+     let's own is renamed. *)
+  prints "a later outer name of the same spelling renames the let's"
+    "(defn f [x i32] () (let [x 1] (g x)) (h x))" "  let x-2 = 1\n  g(x-2)\n  h(x)";
+  prints "the inner let of a chain renamed"
+    "(defn f [] () (let [a 1] (let [b 2] (g b)) (h b)))" "  let a = 1\n  let b-2 = 2\n  g(b-2)\n  h(b)";
+  prints "the binding's own value keeps the outer name"
+    "(defn f [x i32] () (let [x (+ x 1)] (g x)) (h x))" "  let x-2 = x + 1\n  g(x-2)\n  h(x)";
+  prints "a later binding's value takes the new name"
+    "(defn f [x i32] () (let [x 1 y (+ x 1)] (g y)) (h x))"
+    "  let x-2 = 1\n  let y = x-2 + 1\n  g(y)\n  h(x)";
+  prints "the new name is one the function does not use"
+    "(defn f [x i32] () (let [x 1] (g x x-2)) (h x))" "  let x-3 = 1\n  g(x-3, x-2)\n  h(x)";
+  prints "a later let of the same name is no mention"
+    "(defn f [] () (let [a 1] (g a)) (let [a 2] (k a)))" "  let a = 1\n  g(a)\n  let a = 2\n  k(a)";
+  prints "unless its value uses the name"
+    "(defn f [a i32] () (let [a 1] (g a)) (let [a (+ a 1)] (k a)))"
+    "  let a-2 = 1\n  g(a-2)\n  let a = a + 1\n  k(a)";
+  prints "a destructured name renamed alone" "(defn f [] () (let [[p q] v] (g p q)) (h q))"
+    "  let [p q-2] = v\n  g(p, q-2)\n  h(q)";
+  prints "a qualified name counts" "(defn f [] () (let [p (pt)] (g p)) (h p/x))"
+    "  let p-2 = pt()\n  g(p-2)\n  h(p/x)";
+  prints "a quoted name later counts" "(defn f [] () (let [a 1] (g a)) (h 'a))"
+    "  let a-2 = 1\n  g(a-2)\n  h('a)";
+  (* Where a rename cannot be trusted, a do: block holds the let. *)
+  prints "a quoted name inside is not renamed" "(defn f [] () (let [a 1] (g 'a)) (h a))"
+    "  do:\n    let a = 1\n    g('a)\n  h(a)";
+  prints "a call of the name inside is not renamed" "(defn f [] () (let [len 1] (len v)) (h len))"
+    "  do:\n    let len = 1\n    len(v)\n  h(len)";
+  (* A struct pattern renames as pairs, so the field keeps its name. *)
+  prints "a struct pattern renamed"
+    "(defn f [x i32] () (let [{.x .y} p] (g x y)) (h x))" "  let {x-2 .x y .y} = p\n  g(x-2, y)\n  h(x)";
+  prints "a :keys pattern renamed"
+    "(defn f [x i32] () (let [{:keys [x y]} p] (g x y)) (h x))" "  let {x-2 .x y .y} = p\n  g(x-2, y)\n  h(x)";
+  prints "a struct pattern that binds none of them stays"
+    "(defn f [x i32] () (let [{.y .z} p] (g y)) (h x))" "  let {.y .z} = p\n  g(y)\n  h(x)";
+  prints "a later struct pattern rebinding the name is no mention"
+    "(defn f [] () (let [x 1] (g x)) (let [{.x} p] (k x)))" "  let x = 1\n  g(x)\n  let {.x} = p\n  k(x)";
+  prints "a struct literal inside is renamed"
+    "(defn f [x i32] () (let [x 1] (g (P {.x x}))) (h x))" "  let x-2 = 1\n  g(P{.x x-2})\n  h(x)";
+  (* A macro whose body its definition splices into a do is a body run in
+     order; one that splices it anywhere else is not. *)
+  prints "a macro's in-order body"
+    "(defmacro twice [n & body] `(do ~@body ~@body))\n(defn f [] () (twice 2 (let [a 1] (g a)) (h)))"
+    "  twice(2):\n    let a = 1\n    g(a)\n    h()";
+  prints "a macro's list of arguments"
+    "(defmacro listed [& xs] `(list ~@xs))\n(defn f [] () (listed (let [a 1] (g a)) (set x 2)))"
+    "  listed:\n    do:\n      let a = 1\n      g(a)\n    x = 2";
+  prints "comment is a body in order" "(comment (let [a 1] (g a)) (h))" "comment:\n  let a = 1\n  g(a)\n  h()";
+  prints "a later lambda keeps the outer name"
+    "(defn f [] i32 (let [x 1] (let [x 5] (g x)) (app (fn [y] (+ x y)) 2)))"
+    "  let x = 1\n  let x-2 = 5\n  g(x-2)\n  app(fn(y) = x + y, 2)";
+  prints "a renamed name renamed again counts on"
+    "(defn f [] () (let [x 1] (let [x 2] (let [x 3] (g x)) (g x)) (g x)))"
+    "  let x = 1\n  let x-2 = 2\n  let x-3 = 3\n  g(x-3)\n  g(x-2)\n  g(x)";
+  prints "a macro that names the let's name keeps its scope"
+    "(defmacro show-it [] `(println it))\n(defn f [] () (let [it 1] (let [it 2] (show-it)) (show-it)))"
+    "  let it = 1\n  do:\n    let it = 2\n    show-it()\n  show-it()";
+  (* Which macros take a body run in order, read off their definitions. *)
+  let body name src want =
+    let t = Body_macros.table (Reader.read_all ~file:"<m>" src) in
+    let got = Hashtbl.find_opt t.Body_macros.bodies name in
+    if got <> want then
+      fail "%s: body at %s, wanted %s" name
+        (match got with Some k -> string_of_int k | None -> "none")
+        (match want with Some k -> string_of_int k | None -> "none")
+  in
+  body "twice" "(defmacro twice [n & b] `(do ~@b ~@b))" (Some 1);
+  body "tail" "(defmacro tail [& a] `(let [x ~(at a 0)] ~@(form-rest a 1)))" (Some 1);
+  body "nested" "(defmacro inner [& b] `(do ~@b))\n(defmacro nested [& b] `(inner ~@b))" (Some 0);
+  body "listed" "(defmacro listed [& b] `(list ~@b))" None;
+  body "vtwice" "(defmacro vtwice [& b] `(do ~@b (println (length [~@b]))))" None;
+  body "counted" "(defmacro counted [& b] (let [n (length b)] `(do ~n ~@b)))" None;
+  body "counts" "(defmacro counts [& b] (if (= (length b) 2) `(do) `(do ~@b)))" None;
+  body "guarded" "(defmacro guarded [& b] (if (< (length b) 1) `(do) `(do ~@b)))" (Some 0);
+  body "labelled" "(defmacro labelled [& b] `(while :l ~@b))" None;
+  body "labelled-test" "(defmacro labelled-test [& b] `(while :l true ~@b))" (Some 0);
+  body "reads-body" "(defmacro reads-body [& b] `(do ~(at b 0) ~@b))" None;
+  body "unless" "" (Some 1);
+  body "comment" "" (Some 0);
+  body "with-drawing"
+    "(defmacro with-drawing [& args]\n  (if (or (< (length args) 1) (and (= (length args) 1) (form-empty-list? (at args 0))))\n    `(takes-a-body)\n    `(do (begin) ~@args (end))))"
+    (Some 0);
+  prints "in a quasiquote" "(defmacro m [x] (quasiquote (do (let [a 1] (g a)) (h ~x))))"
+    "  do:\n      let a = 1\n      g(a)\n    h(~x)";
+  prints "among a call's arguments" "(foo 1 (let [a 1] (g a)) (set x 2))"
+    "foo(1):\n  do:\n    let a = 1\n    g(a)\n  x = 2";
+  prints "at the top level" "(let [a 1] (g a))\n(h)" "do:\n  let a = 1\n  g(a)\n\nh()";
+  prints "one-argument and" "(defn f [] () (while (and (< i n)) (g)))" "  while i < n\n";
+  prints "one-argument or" "(defn f [] () (when (or c) (g)))" "  if c\n";
+  prints "one-argument and in a quasiquote" "(defmacro m [x] (quasiquote (and ~x)))" "and(~x)";
   prints "do in an arm is a block" "(defn f [] () (match s _ (do (a) (b))))" "_ ->\n      a()";
   prints "hex spelling" "(def c dyn 0xFFF00FFF)" "0xFFF00FFF";
   prints "own-line comment above its form" "(defn f [] ()\n  ;; why\n  (g))" "  ;; why\n  g()";
@@ -681,8 +941,41 @@ let run_both path want =
              (if x86 then " --x86" else "") text code want)
     [ false; true ]
 
+(* A program and its conversion print the same: the flat lets, the renames
+   and the macro bodies they rest on keep what each name means. *)
+let run_converted path =
+  let run p =
+    let exe = Filename.concat scratch
+        (Printf.sprintf "flan-flat-%s-%d" (Filename.basename p) (Unix.getpid ())) in
+    let prog, csrcs, lflags = Test_support.linked p in
+    ignore (Build.executable ~opts:Build.default ~csrcs ~lflags prog ~out:exe);
+    let out = exe ^ ".out" in
+    let code = Sys.command (Filename.quote exe ^ " > " ^ Filename.quote out ^ " 2>&1") in
+    let text = In_channel.with_open_bin out In_channel.input_all in
+    (try Sys.remove out; Sys.remove exe with Sys_error _ -> ());
+    (code, text)
+  in
+  match
+    let forms = Reader.read_file path in
+    let source = In_channel.with_open_bin path In_channel.input_all in
+    let macros = Body_macros.table ~file:path forms in
+    let fln = Filename.concat scratch
+        (Printf.sprintf "%d-%s.fln" (Unix.getpid ()) (Filename.remove_extension (Filename.basename path))) in
+    Out_channel.with_open_bin fln (fun oc ->
+        output_string oc (Indent_printer.program ~source ~macros forms));
+    let a = run path and b = run fln in
+    (try Sys.remove fln with Sys_error _ -> ());
+    (a, b)
+  with
+  | exception e -> fail "%s converted: %s" path (diag_text e)
+  | ((0, a), (0, b)) when a = b -> ()
+  | ((c, a), (d, b)) ->
+    fail "%s printed %S (exit %d), and converted %S (exit %d)" path a c b d
+
 let () =
   if Test_support.have "clang" then begin
+    List.iter run_converted
+      [ "syntax/flat/shadows.flan"; "syntax/flat/macros.flan"; "syntax/flat/capture.flan" ];
     run_both "syntax/mixed/main.flan" "12\n12\n0\n55\n";
     run_both "syntax/mixed/main.fln" "25\n7\nfar\n3\n"
   end