From c1916ed819e7a0ca579c387710528d9fe37c6598 Mon Sep 17 00:00:00 2001
From: Joseph Ferano <joseph@ferano.io>
Date: Sat, 26 Sep 2026 17:07:01 +0700
Subject: [PATCH] e as g is any test of a condition's and chain, binding g for
 the rest of the chain and the block.

---
 TODO.org                       |   5 ++
 emacs/flan-fln-mode.el         |  16 +++-
 emacs/test-flan-fln.el         |  10 +++
 lib/ast.ml                     |  15 ++++
 lib/check.ml                   |  83 ++++++++++++++++++-
 lib/indent_reader.ml           | 147 +++++++++++++++++++++------------
 lib/load.ml                    |   4 +-
 lib/parse.ml                   |  24 ++++++
 spec-syntax.md                 |  32 +++++--
 test/programs/as-chain-dyn.fln |  31 +++++++
 test/programs/as-chain.fln     |  90 ++++++++++++++++++++
 test/test_acceptance.ml        |   7 +-
 test/test_syntax.ml            |  48 ++++++++---
 13 files changed, 435 insertions(+), 77 deletions(-)
 create mode 100644 test/programs/as-chain-dyn.fln
 create mode 100644 test/programs/as-chain.fln

diff --git a/TODO.org b/TODO.org
index c54bcdc7..fb813245 100644
--- a/TODO.org
+++ b/TODO.org
@@ -34,6 +34,11 @@ Decided (133): =x?= is a bool; =if x?=, =elif x?=, =while x?= and the rest of an
 make a local Option its payload in the block, in place (not a copy). Assigning an Option
 to it there is refused rather than ending the narrowing; =e? as g= names what a test
 found. Rules out =if let g = x= over a plain name, which is refused toward these.
+** DONE e as g inside an and chain
+CLOSED: [2026-09-26]
+Decided (136): =e as g= (or =e? as g=) is any test of a condition's =and= chain, binding =g=
+for the rest of the chain and the block, and a kept =when= with one is one flat Option. Rules
+out =as= as a cast (only an Option or a dyn), and a binding under =or=, =not= or =until=.
 ** TODO The stepper does not step inside an optional chain
 =Ast.step_expr= treats a =Chain= as a leaf (its catch-all), so nothing in a chain's
 body gets a step point of its own.
diff --git a/emacs/flan-fln-mode.el b/emacs/flan-fln-mode.el
index fe93577d..1c53b045 100644
--- a/emacs/flan-fln-mode.el
+++ b/emacs/flan-fln-mode.el
@@ -1807,6 +1807,19 @@ it, so a block pasted at another depth stays one block."
 (defun flan-fln--fallback-re (heads)
   (concat "^" (regexp-opt heads t) "(" flan-fln--name-re))
 
+(defun flan-fln--as-matcher (limit)
+  "Find the next `as' of a condition up to LIMIT, `if e as g and ...': an
+`as' before a name, on a line an `if', `elif', `while' or `when' comes first on."
+  (let (found)
+    (while (and (not found)
+                (re-search-forward "[ \t]\\(as\\)[ \t]+[^][ \t\n(){},;\":]" limit t))
+      (setq found (save-excursion
+                    (save-match-data
+                      (goto-char (match-beginning 1))
+                      (re-search-backward "\\_<\\(?:if\\|elif\\|while\\|when\\)\\_>"
+                                          (line-beginning-position) t)))))
+    found))
+
 (defun flan-fln--return-type-matcher (limit)
   "Find the next return type up to LIMIT: after the `->' of a fn header, a
 lambda or a `Fn(...)' type, and not after a match arm's."
@@ -1881,8 +1894,9 @@ lambda or a `Fn(...)' type, and not after a match arm's."
     ;; The words inside a line: `for i in range(n)', `if c then a else b', a
     ;; `where' constraint.
     ("[ \t]\\(then\\|else\\|in\\|where\\)[ \t]" 1 font-lock-keyword-face)
-    ;; A test's `as', `if e? as g'.
+    ;; A test's `as', `if e? as g', and a condition's, `if e as g and ...'.
     ("?[ \t]+\\(as\\)[ \t]" 1 font-lock-keyword-face)
+    (flan-fln--as-matcher 1 font-lock-keyword-face)
     ;; `if let Some(g) = x', and a value's `if' or `when', `x = when c then a'.
     ("\\_<\\(?:el\\)?if[ \t]+\\(let\\)[ \t]" 1 font-lock-keyword-face)
     ("[ \t=(,]\\(if\\|when\\)[ \t]" 1 font-lock-keyword-face)
diff --git a/emacs/test-flan-fln.el b/emacs/test-flan-fln.el
index 42ec72af..4a6a4fbe 100644
--- a/emacs/test-flan-fln.el
+++ b/emacs/test-flan-fln.el
@@ -938,6 +938,16 @@ defconst(k, 3)
   (search-forward "g!")
   (backward-char 1)
   (test-flan-fln--is "the name at x! is x" (thing-at-point 'symbol t) "g"))
+;; A condition's `as' with no `?' before it, twice on a line; an `as' outside
+;; a condition is left alone.
+(test-flan-fln--in "fn f()\n  left = when get(grid, r) as g and b(g) as h then g\n  x = as y\n"
+  (font-lock-ensure)
+  (let ((face (lambda (needle)
+                (save-excursion (goto-char (point-min)) (search-forward needle)
+                                (get-text-property (match-beginning 0) 'face)))))
+    (test-flan-fln--is "a condition's as is a keyword" (funcall face "as g") 'font-lock-keyword-face)
+    (test-flan-fln--is "and a second one" (funcall face "as h") 'font-lock-keyword-face)
+    (test-flan-fln--is "an as outside a condition is not" (funcall face "as y") nil)))
 (test-flan-fln--is "after if x? as g, one level deeper"
                    (test-flan-fln--tabs "fn f() -> ()\n  if o? as g\n|" 1) 4)
 (with-temp-buffer
diff --git a/lib/ast.ml b/lib/ast.ml
index 2d85db01..e20f43e4 100644
--- a/lib/ast.ml
+++ b/lib/ast.ml
@@ -632,3 +632,18 @@ let mark_pause ?fn ~line ~col (ds : decl list) : decl list option =
   in
   let ds = List.map decl ds in
   if !hit then Some ds else None
+
+(* The names the [as] tests of condition [c] bind (decision 136), for the
+   block [c] guards. [Parse.as_chain] reads the chain to this shape: each
+   test an [If] with [false] for its else, each [as] an [IfLet] over a plain
+   name with the rest of the chain as its body and [false] for its else. *)
+let as_name g =
+  g <> "" && (match g.[0] with 'A' .. 'Z' -> false | _ -> true)
+  && g <> "true" && g <> "false"
+
+let rec as_binds (c : expr) =
+  match c.e with
+  | If (_, q, Some { e = Var "false"; _ }) -> as_binds q
+  | IfLet (_, { pat = Pctor (g, []); body = [ q ]; _ }, Some { e = Var "false"; _ })
+    when as_name g -> g :: as_binds q
+  | _ -> []
diff --git a/lib/check.ml b/lib/check.ml
index 48360e96..8771c299 100644
--- a/lib/check.ml
+++ b/lib/check.ml
@@ -6480,7 +6480,7 @@ and check_value ctx ?want (e : Ast.expr) : Tast.expr =
           fail loc
             "%s is tested with %s? above, so in this block it is %s, and it \
              cannot be given an Option here: the block reads it as present \
-             throughout. Assign a %s, or test a new name, as in while %s? as \
+             throughout. Assign a %s, or test a new name, as in while %s as \
              item, and assign %s from that"
             n n (tyname loc b.bty) (tyname loc b.bty) n n
         | _ -> raise (Loc.Error d)))
@@ -8525,12 +8525,29 @@ and check_if ctx ?(tail = false) ?(used = false) ?want loc c t e =
            raise ex)
 
 and check_if_once ctx ~tail ~used ?want loc c t e =
+  if as_binds c = [] then check_if_tested ctx ~tail ~used ?want loc c t e
+  else scoped ctx (fun () -> check_if_tested ctx ~tail ~used ?want loc c t e)
+
+and check_if_tested ctx ~tail ~used ?want loc c t e =
   let t =
     match narrows c with
     | [] -> t
     | names -> { t with Ast.e = Ast.Narrow (names, t) }
   in
-  let c = check_truthy ctx c in
+  let c, t =
+    match as_binds c with
+    | [] -> (check_truthy ctx c, t)
+    | _ ->
+      (* What an [as] named reaches the block through a name no reader can
+         write, bound in the scope this if was given; the else is checked
+         without it. *)
+      let cv, named = as_cond ctx c in
+      let bnd (g, h) =
+        { Ast.bname = g; bty = None; bval = { Ast.e = Ast.Var h; loc = t.Ast.loc };
+          bloc = t.Ast.loc }
+      in
+      (cv, { t with Ast.e = Ast.Let (List.map bnd named, [ t ]) })
+  in
   (* Both arms are the tail, and a one-armed [if] counts: [(when c (recur ...))]
      is how nearly every loop is written, and the branch is still the last
      thing the body does. Both arms are kept when the [if] is. *)
@@ -10673,8 +10690,68 @@ and narrows (c : Ast.expr) =
   match c.Ast.e with
   | Ast.Call ({ Ast.e = Ast.Var "?"; _ }, [ { Ast.e = Ast.Var x; _ } ]) -> [ x ]
   | Ast.If (p, q, Some { Ast.e = Ast.Var "false"; _ }) -> narrows p @ narrows q
+  | Ast.IfLet (_, { Ast.pat = Ast.Pctor (g, []); body = [ q ]; _ },
+               Some { Ast.e = Ast.Var "false"; _ }) when as_name g -> narrows q
   | _ -> []
 
+and as_binds c = Ast.as_binds c
+
+and as_name g = Ast.as_name g
+
+(* A condition with [as] in it, as the bool it tests, and each name it binds
+   with the hidden name the block reads it through. The chain runs left to
+   right and stops at the first test that fails, so each value is found
+   once; what an [as] finds is copied into its name's slot there, and a
+   later test and the block read that slot. *)
+and as_cond ctx (c : Ast.expr) =
+  let named = ref [] in
+  let no loc = mk loc Types.Bool (Tast.Bool false) in
+  let rec go (c : Ast.expr) =
+    let loc = c.Ast.loc in
+    match c.Ast.e with
+    | Ast.If (p, q, Some { Ast.e = Ast.Var "false"; _ }) when as_binds q <> [] ->
+      let pv = check_truthy ctx p in
+      let qv = with_narrowed ctx (narrows p) (fun () -> go q) in
+      mk loc Types.Bool (Tast.If (pv, qv, no loc))
+    | Ast.IfLet (e, { Ast.pat = Ast.Pctor (g, []); body = [ q ]; _ },
+                 Some { Ast.e = Ast.Var "false"; _ }) when as_name g ->
+      let ev = check ctx e in
+      let hs = fresh_slot ctx ev.Tast.ty in
+      let hv = mk loc ev.Tast.ty (Tast.Local hs) in
+      let test, payload, ty =
+        match ev.Tast.ty with
+        | Types.Option t -> (opt_is_some loc hv, opt_payload loc t hv, t)
+        | Types.Dyn -> (dyn_not_nil loc hv, hv, Types.Dyn)
+        | t ->
+          Loc.failk "check/as-not-optional" e.Ast.loc
+            "%s is %s, which always holds a value, so as has nothing to test. \
+             as names what an Option or a dyn holds, when it holds something. \
+             It is not a conversion: a number is converted with its type's \
+             name, as in i32(x)"
+            (source_text e) (tyname loc t)
+      in
+      let slot, qv =
+        scoped ctx (fun () ->
+            let slot = bind ctx g ty ~assignable:false in
+            (match lookup ctx g with
+             | Some b ->
+               incr held_n;
+               named := (g, Printf.sprintf "~as%d" !held_n, b) :: !named
+             | None -> ());
+            (slot, go q))
+      in
+      mk loc Types.Bool
+        (Tast.Let ([ (hs, ev) ],
+                   [ mk loc Types.Bool
+                       (Tast.If (test, mk loc Types.Bool (Tast.Let ([ (slot, payload) ], [ qv ])),
+                                 no loc)) ]))
+    | _ -> check_truthy ctx c
+  in
+  let cv = go c in
+  let named = List.rev !named in
+  List.iter (fun (_, h, b) -> ctx.scope <- (h, b) :: ctx.scope) named;
+  (cv, List.map (fun (g, h, _) -> (g, h)) named)
+
 (* [f] with each of [names] that is a local (Option T) read as its payload:
    the same slot, so a field set through it lands in the Option itself. A
    dyn stays as it is; a name that is not a local is not narrowed. Assigning
@@ -10717,7 +10794,7 @@ and with_narrowed : 'a. ctx -> string list -> (unit -> 'a) -> 'a = fun ctx names
                           (Printf.sprintf
                              "%s? does not make %s its payload here: %s's address \
                               is taken, or a fn assigns it, in this function, so \
-                              something else could clear it. Write if %s? as g, \
+                              something else could clear it. Write if %s as g, \
                               which copies what it holds into g"
                              n n n n) ] }
             in
diff --git a/lib/indent_reader.ml b/lib/indent_reader.ml
index 3898b753..448d3ba8 100644
--- a/lib/indent_reader.ml
+++ b/lib/indent_reader.ml
@@ -994,7 +994,7 @@ let no_place (e : Form.t) =
     failk "chain-assign" e.loc
       "%s is an optional chain, and a chain cannot be assigned to: when it \
        holds nothing there is no place to write. Test it first: if %s?, and \
-       in the block %s is what it holds, or if %s? as g, then assign through g"
+       in the block %s is what it holds, or if %s as g, then assign through g"
       (text_of e) r r r
   | Form.List [ { v = Form.Sym "!!"; _ }; x ] ->
     let r = text_of x in
@@ -1376,12 +1376,7 @@ and if_expr p =
   let t = advance p in
   let word = match t.tok with NAME w -> w | _ -> "if" in
   let letp = if word = "if" then if_let_head p else None in
-  let c = match letp with Some m -> m | None -> fst (binary p 1) in
-  let letp, c =
-    match letp with
-    | Some _ -> (letp, c)
-    | None -> (match as_head p c with Some m when word = "if" -> (Some m, m) | _ -> (None, c))
-  in
+  let c = match letp with Some m -> m | None -> cond_head p in
   (match (peek p).tok with
    | NAME "then" -> ignore (advance p)
    | _ ->
@@ -1422,35 +1417,79 @@ and if_let_head p =
        failk "if-let-name" pat.loc
          "if let %s = %s has no pattern to test. To test that %s holds a \
           value, write if %s?, and in the block it is what it holds; to name \
-          what it holds, write if %s? as %s"
+          what it holds, write if %s as %s"
          g (text_of v) (text_of v) (text_of v) (text_of v) g
      | _ -> ());
     Some (mk p lt.loc (Form.Vec [ pat; v ]))
   | _ -> None
 
-(* [e? as g]: after a test [e?], the name what [e] holds is bound to, as
-   the head [[g e]] an [if let] over a plain name stands as (decision 133). *)
-and as_head p (c : Form.t) =
+(* A condition, where [e as g] may stand as a test of a top-level [and]
+   chain (decisions 133, 136): [e] holds a value, and [g] names it for the
+   rest of the chain and the block. [e? as g] is the same test. Each binding
+   reads [(as g e)] in its test's place, in one flat [(and ...)]; the checker
+   gives [g] its scope. It cannot stand under [or] or [not], where the test
+   holding would not mean [e] held anything. *)
+and cond_head p =
+  let x, lvl = binary p 1 in
   match (peek p).tok with
-  | NAME "as" ->
-    let at = advance p in
-    (match c.v with
-     | Form.List [ { v = Form.Sym "?"; _ }; e ] ->
-       let g =
-         match (peek p).tok with
-         | NAME g when g <> "" && g.[0] <> '.' ->
-           let gt = advance p in
-           check_name gt g;
-           sym gt.loc g
-         | tk ->
-           failk "as-name" (where_ p) "as takes the name to bind, and found %s" (show tk)
-       in
-       Some (Form.make (Form.Vec [ g; e ]) c.loc)
-     | _ ->
-       failk "as-test" at.loc
-         "as names what a test found, and %s is not one. Write %s? as name"
-         (text_of c) (text_of c))
-  | _ -> None
+  | NAME "as" -> as_chain p x lvl
+  | _ -> x
+
+and as_chain p (x : Form.t) lvl =
+  let at = advance p in
+  let refuse_or loc =
+    failk "as-or" loc
+      "as names what a test found, for the rest of an and chain and the \
+       block. With or, the block can run when that test did not hold, and \
+       there would be nothing to name. Bind with as in an if of its own, and \
+       test the rest inside it"
+  in
+  let items (f : Form.t) =
+    match f.v with
+    | Form.List ({ v = Form.Sym "and"; _ } :: (_ :: _ as xs)) -> xs
+    | _ -> [ f ]
+  in
+  if lvl = 1 then refuse_or x.loc;
+  let before, last =
+    match List.rev (if lvl = 2 then items x else [ x ]) with
+    | last :: rb -> (List.rev rb, last)
+    | [] -> ([], x)
+  in
+  (match last.v with
+   | Form.List ({ v = Form.Sym "not"; _ } :: _) ->
+     failk "as-not" at.loc
+       "as names what a test found, and not turns the test around: the \
+        block runs when %s holds nothing, so there is nothing to name. Bind \
+        with as, and put what runs when it is absent in the else"
+       (text_of last)
+   | Form.List ({ v = Form.Sym "or"; _ } :: _) -> refuse_or last.loc
+   | _ -> ());
+  let e = match last.v with Form.List [ { v = Form.Sym "?"; _ }; e ] -> e | _ -> last in
+  let g =
+    match (peek p).tok with
+    | NAME g when g <> "" && g.[0] <> '.' && not (is_op_word g) ->
+      let gt = advance p in
+      check_name gt g;
+      sym gt.loc g
+    | tk -> failk "as-name" (where_ p) "as takes the name to bind, and found %s" (show tk)
+  in
+  let bound = Form.make (Form.List [ sym at.loc "as"; g; e ]) last.loc in
+  let rest =
+    match (peek p).tok with
+    | NAME "and" ->
+      ignore (advance p);
+      let y, ylvl = binary p 1 in
+      (match (peek p).tok with
+       | NAME "as" -> items (as_chain p y ylvl)
+       | _ ->
+         if ylvl = 1 then refuse_or y.loc;
+         if ylvl = 2 then items y else [ y ])
+    | NAME "or" -> refuse_or (peek p).loc
+    | _ -> []
+  in
+  match before @ (bound :: rest) with
+  | [ one ] -> one
+  | xs -> Form.make (Form.List (sym x.loc "and" :: xs)) x.loc
 
 (* The if an [if let] head was read into, rewritten to (if-let [P v] then
    else): [(if [P v] a b)], [(when [P v] body ...)] and an elif chain's
@@ -2691,12 +2730,7 @@ and header (s : st) w : Form.t =
     form [ alias; path ]
   | "if" | "when" ->
     let letp = if w = "if" then if_let_head p else None in
-    let c = match letp with Some m -> m | None -> fst (binary p 1) in
-    let letp, c =
-      match letp with
-      | Some _ -> (letp, c)
-      | None -> (match as_head p c with Some m when w = "if" -> (Some m, m) | _ -> (None, c))
-    in
+    let c = match letp with Some m -> m | None -> cond_head p in
     (* The elif and else clauses at the if's column, then the whole form.
        [oneline] when the if was [if c then a]: its clauses may then be
        one-line too, [elif c then x] and [else y], or take blocks. *)
@@ -2713,11 +2747,7 @@ and header (s : st) w : Form.t =
           let c =
             match if_let_head p with
             | Some m -> elif_lets := m :: !elif_lets; m
-            | None ->
-              let c = fst (binary p 1) in
-              (match as_head p c with
-               | Some m -> elif_lets := m :: !elif_lets; m
-               | None -> c)
+            | None -> cond_head p
           in
           (match (peek p).tok with
            | NAME "then" when oneline ->
@@ -2829,21 +2859,30 @@ and header (s : st) w : Form.t =
       | KW k, n when n <> NEWLINE -> let kt = advance p in [ Form.make (Form.Kw k) kt.loc ]
       | _ -> []
     in
-    let c, _ = expr p in
-    (match (if w = "while" then as_head p c else None) with
-    (* [while e? as g]: [(while true (if-let [g e] (do body) (break)))]. A
-       break or continue in the body is this loop's. *)
-    | Some m ->
-      expect_line_end p ~after:(w ^ " " ^ text_of c ^ " as ...");
-      let body = block s ~after:w in
+    let c = cond_head p in
+    let binds =
+      let is_as (f : Form.t) =
+        match f.v with Form.List ({ v = Form.Sym "as"; _ } :: _) -> true | _ -> false
+      in
+      match c.v with
+      | Form.List ({ v = Form.Sym "and"; _ } :: xs) -> List.exists is_as xs
+      | _ -> is_as c
+    in
+    if binds && w = "until" then
+      failk "as-until" c.Form.loc
+        "until runs while its test does not hold, so as would name what a \
+         test found when it found nothing. Write while, with the test the \
+         other way round";
+    expect_line_end p ~after:(w ^ " " ^ text_of c);
+    let body = block s ~after:w in
+    if binds then
+      (* [while c]: [(while true (if c (do body) (break)))], so what [c]
+         binds reaches the body. A break or continue in the body is this
+         loop's, and a continue tests [c] again. *)
       let at = c.Form.loc in
       let f items = Form.make (Form.List items) at in
-      form (label @ [ sym at "true";
-                      f [ sym at "if-let"; m; f (sym at "do" :: body); f [ sym at "break" ] ] ])
-    | None ->
-      expect_line_end p ~after:(w ^ " " ^ text_of c);
-      let body = block s ~after:w in
-      form (label @ (c :: body)))
+      form (label @ [ sym at "true"; f [ sym at "if"; c; f (sym at "do" :: body); f [ sym at "break" ] ] ])
+    else form (label @ (c :: body))
   | "for" ->
     let label =
       match (peek p).tok with
diff --git a/lib/load.ml b/lib/load.ml
index 1ac7734c..1809fecc 100644
--- a/lib/load.ml
+++ b/lib/load.ml
@@ -255,7 +255,9 @@ let rec rename_expr owned alias bound (e : Ast.expr) : Ast.expr =
           (bound, []) bs
       in
       Ast.Let (List.rev bs, List.map (rename_expr owned alias bound) body)
-    | Ast.If (c, t, e') -> Ast.If (go c, go t, Option.map go e')
+    (* What an [as] in the condition binds is bound in the block. *)
+    | Ast.If (c, t, e') ->
+      Ast.If (go c, rename_expr owned alias (Ast.as_binds c @ bound) t, Option.map go e')
     | Ast.While (l, c, body) -> Ast.While (l, go c, gos body)
     (* A loop's names are its own and are never imported; its initial
        values and its body are ordinary expressions. *)
diff --git a/lib/parse.ml b/lib/parse.ml
index 757f8803..f34cefde 100644
--- a/lib/parse.ml
+++ b/lib/parse.ml
@@ -508,6 +508,8 @@ and form f mk (head : Form.t) (args : Form.t list) : Ast.expr =
      | _ -> fail f "?. is (?. [name value] body)")
 
   (* Short-circuiting, so they cannot be ordinary calls. *)
+  | Sym "and" when List.exists is_as args -> as_chain f args
+  | Sym "as" -> as_chain f [ f ]
   | Sym "and" -> shortcircuit f args ~is_and:true
   | Sym "or" -> shortcircuit f args ~is_and:false
 
@@ -1303,6 +1305,28 @@ and cond f (args : Form.t list) : Ast.expr =
    actually fix it is check_if preferring the arm that is not a compiler temp
    when it reports, which is check.ml's call. Written up in TODO.org, "and's
    last operand gets a misdirected caret". *)
+(* [(as g e)]: the test that [e] holds a value, naming it [g] (decision
+   136). The reader writes one only as a condition or a test of the [and]
+   chain that is one. Each test of that chain is an [If] whose else is
+   [false], and each [as] an [IfLet] over the plain name [g] whose body is
+   the rest of the chain and whose else is [false]; [Check.as_cond] reads
+   that shape and gives [g] to the block the condition guards as well. *)
+and is_as (f : Form.t) =
+  match f.v with List ({ v = Sym "as"; _ } :: _) -> true | _ -> false
+
+and as_chain f (args : Form.t list) : Ast.expr =
+  let no (x : Form.t) = { Ast.e = Ast.Var "false"; loc = x.loc } in
+  let rec go = function
+    | [] -> { Ast.e = Ast.Var "true"; loc = f.loc }
+    | [ x ] when not (is_as x) -> expr x
+    | ({ v = List [ { v = Sym "as"; _ }; { v = Sym g; _ }; e ]; _ } as x) :: rest ->
+      let arm = { Ast.pat = Ast.Pctor (g, []); body = [ go rest ]; aloc = x.loc } in
+      { Ast.e = Ast.IfLet (expr e, arm, Some (no x)); loc = x.loc }
+    | x :: _ when is_as x -> fail x "as is (as name value)"
+    | x :: rest -> { Ast.e = Ast.If (expr x, go rest, Some (no x)); loc = x.loc }
+  in
+  go args
+
 and shortcircuit f (args : Form.t list) ~is_and : Ast.expr =
   let mk e = { Ast.e; loc = f.loc } in
   let rec go = function
diff --git a/spec-syntax.md b/spec-syntax.md
index d6b13f7d..cca64da6 100644
--- a/spec-syntax.md
+++ b/spec-syntax.md
@@ -287,7 +287,7 @@ Each item: the proposal, then the reason in one line.
   Kept with no `else` at the end of its chain, it gives an Option as `when` does.
   `P` is any `match` pattern, and its names are bound in the block only. One
   line: `if let Some(g) = o then g else 0`. A plain name, `if let g = o`, is
-  refused toward `if o?` and `if o? as g` below; `_` is refused toward `let`.
+  refused toward `if o?` and `if o as g` below; `_` is refused toward `let`.
   **Built.**
 - **`x?` tests that a value is present** (decision 133): a bool, true when an
   Option is `Some` and when a dyn is not `nil`. It reads `(? x)`. In `if x?`,
@@ -299,15 +299,33 @@ Each item: the proposal, then the reason in one line.
   present; giving it an Option is refused, and a parameter or a captured copy
   is no more assignable than outside it. A local whose address is taken, or
   that a `fn` assigns, anywhere in the function is not narrowed (something
-  else could clear it); `if x? as g` copies what it holds instead. A `?` after
+  else could clear it); `if x as g` copies what it holds instead. A `?` after
   a chain tests the whole chain: `o?.i?`. A capitalised name before `?` is
   read as a type, so a local tested this way needs a lowercase name.
   **Built.**
-- **`e? as g`** names what a test found, for an `e` that is not a plain name:
-  `if get(grid, r, c)? as cell` reads `(if-let [cell (get grid r c)] …)`, an
-  `if-let` over a plain name, which binds what an Option holds or a dyn that
-  is not `nil`. It works after `if`, `elif` and `while`; `while e? as g` plus
-  a block reads `(while true (if-let [g e] (do …) (break)))`. **Built.**
+- **`e as g`** tests that `e` holds a value and names it `g` (decisions 133,
+  136): an Option that is `Some` binds its payload, a dyn that is not `nil`
+  binds itself. `e? as g` is the same test. Over any other type it is
+  refused; `as` is never a conversion, which is written `i32(x)`. It stands
+  after `if`, `elif`, `while` and a one-line `if … then` or kept `when`, as
+  the whole condition or as any test of an `and` chain, and `g` is bound for
+  the rest of that chain and for the block: Swift's `if let g = e, c`.
+
+  ```
+  if get(grid, r + 1, c - 1) as g and is-empty-cell(g)
+    move(g)
+  if a as x and b as y and x < y
+    println(x, y)
+  let left = when get(grid, r + 1, c - 1) as g and is-empty-cell(g) then g
+  ```
+
+  The tests run left to right and stop at the first that fails, so each
+  value is found once. `g` is not bound in the `else`, in an `elif` or after
+  the block. It is refused under `or` and `not`, and after `until`, where the
+  block could run with nothing found. `x?` on a plain local narrows beside it
+  in the same chain. Reads `(as g e)` in the test's place, `(when (and a (as
+  g e) (f g)) …)`; `while c` with one reads `(while true (if c (do …)
+  (break)))`. **Built.**
 - **`while c`, `until c`**, optional label first: `while :outer c`. **Built.**
 - **`for i in range(n)`**, `range(a, b)`, `range(a, b, step)` read as
   `dotimes`. `range` here is syntax, not a function. `..` is avoided because
diff --git a/test/programs/as-chain-dyn.fln b/test/programs/as-chain-dyn.fln
new file mode 100644
index 00000000..d7805607
--- /dev/null
+++ b/test/programs/as-chain-dyn.fln
@@ -0,0 +1,31 @@
+;; e as g over a dyn inside an and chain (decision 136): g is bound when e
+;; is not nil, for the rest of the chain and the block.
+
+fn pet-name(m)
+  if m.pet as pet and pet != "cat"
+    pet
+  elif m.name as who and who != "bo"
+    who
+  else
+    "nobody"
+
+fn first-big(xs, lo)
+  let found = when get(xs, 0) as x and x > lo then x
+  found
+
+fn run(m, xs, a, b)
+  println(pet-name(m), pet-name({:pet "cat" :name "bo"}), pet-name({:name "ann"}))
+  println(first-big(xs, 0), first-big(xs, 5), first-big([], 0))
+  let i = 0
+  let total = 0
+  while get(xs, i) as x and x > 0
+    total += x
+    i += 1
+  println(total, i)
+  if a? and get(xs, 1) as y and a + y > 4
+    println(a + y)
+  let v = if b as z and z > 1 then z else -1
+  println(v)
+
+fn main()
+  run({:pet "dog" :name "ann"}, [4, 2, 0, 7], 3, nil)
diff --git a/test/programs/as-chain.fln b/test/programs/as-chain.fln
new file mode 100644
index 00000000..eda9bc5b
--- /dev/null
+++ b/test/programs/as-chain.fln
@@ -0,0 +1,90 @@
+;; e as g inside an and chain (decision 136): g is bound for the rest of the
+;; chain and for the block, and not in the else, an elif or after the block.
+;; e? as g is the same test.
+
+struct Grain
+  color-idx: i32
+
+let calls: i32 = 0
+
+fn get-cell(grid: [4 i32], i: i32) -> Grain?
+  calls += 1
+  if i < 0 or i >= 4
+    return None
+  Some(Grain{.color-idx grid[i]})
+
+fn is-empty-cell(g: Grain) -> bool
+  g.color-idx < 0
+
+fn tick(n: i32) -> i32
+  calls += 1
+  print(n, "")
+  n
+
+fn half(n: i32) -> i32?
+  calls += 1
+  if n % 2 == 0 then Some(n / 2) else None
+
+fn classify(grid: [4 i32], i: i32) -> str
+  if get-cell(grid, i) as g and is-empty-cell(g)
+    "empty"
+  elif get-cell(grid, i) as g and g.color-idx > 1
+    "big"
+  elif half(i) as h and h > 0
+    "half"
+  else
+    "other"
+
+fn main()
+  let grid = [1, -1, 2, -3]
+  ;; A block if, with an else that does not see g.
+  let g = 100
+  if get-cell(grid, 1) as g and is-empty-cell(g)
+    println("empty", g.color-idx)
+  if get-cell(grid, 0) as g and is-empty-cell(g)
+    println("empty", g.color-idx)
+  else
+    println("else sees the outer g", g)
+  println("after", g)
+  ;; A kept when gives a Grain?.
+  let left = when get-cell(grid, 3) as g and is-empty-cell(g) then g
+  println(left!.color-idx)
+  let none: Grain? = when get-cell(grid, 0)? as g and is-empty-cell(g) then g
+  println(none?)
+  ;; Two bindings, and a test over both.
+  let a: i32? = Some(3)
+  let b: i32? = Some(5)
+  if a as x and b as y and x < y
+    println(x, y)
+  if a as x and b as y and x > y
+    println(x, y)
+  else
+    println("not less")
+  ;; One line, in a let.
+  let v = if half(8) as h and h > 3 then h * 10 else -1
+  let w = if half(6) as h and h > 3 then h * 10 else -1
+  println(v, w)
+  ;; An elif chain.
+  println(classify(grid, 1), classify(grid, 2), classify(grid, 0), classify(grid, 4), classify(grid, 5))
+  ;; Each value is found once, left to right, and a failed test stops the chain.
+  calls = 0
+  if tick(1) > 0 and half(tick(2)) as h and tick(3) + h > 0
+    println("ran", h)
+  println(calls)
+  calls = 0
+  if tick(1) > 0 and half(tick(3)) as h and tick(5) + h > 0
+    println("ran", h)
+  else
+    println("stopped")
+  println(calls)
+  ;; x? narrows beside as in one chain.
+  let n: i32? = Some(40)
+  if n? and half(n) as h and n + h > 50
+    println(n + h)
+  ;; while: pop while the next cell is empty.
+  let i = 1
+  let seen = 0
+  while get-cell(grid, i) as c and is-empty-cell(c)
+    seen += c.color-idx
+    i += 2
+  println(seen, i)
diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index 1233fb1c..1484a776 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -2275,7 +2275,12 @@ let () =
          outputs ~x86:true (path ^ ", --x86") ("programs/" ^ path) want)
       [ ("optionals.fln", optionals_out); ("optionals-dyn.fln", optionals_dyn_out);
         (* x? tests and narrows, e? as g names what it found (decision 133). *)
-        ("presence.fln", "true false true\n6\n-1\n3\n101 209 0\n11\n42\n2\nabsent\n6\nfalse true\n3\n6\n15\n"); ("presence-dyn.fln", "true false\n103 209 0\nno pet\nann\n3 2\n") ];
+        ("presence.fln", "true false true\n6\n-1\n3\n101 209 0\n11\n42\n2\nabsent\n6\nfalse true\n3\n6\n15\n"); ("presence-dyn.fln", "true false\n103 209 0\nno pet\nann\n3 2\n");
+        (* e as g inside an and chain, typed and dyn (decision 136). *)
+        ("as-chain.fln",
+         "empty -1\nelse sees the outer g 100\nafter 100\n-3\nfalse\n3 5\nnot less\n40 -1\n\
+          empty big other half other\n1 2 3 ran 1\n4\n1 3 stopped\n3\n60\n-4 5\n");
+        ("as-chain-dyn.fln", "dog nobody ann\n4 nil nil\n6 2\n5\n-1\n") ];
     (* x! over nothing traps at its site and names the expression. *)
     List.iter
       (fun (x86, arg, want) ->
diff --git a/test/test_syntax.ml b/test/test_syntax.ml
index d64e413d..8791d8a3 100644
--- a/test/test_syntax.ml
+++ b/test/test_syntax.ml
@@ -1409,21 +1409,49 @@ let () =
      found; if let over a plain name is refused toward those. *)
   refuses "if let over a plain name" "if let g = x\n  g" "indent/if-let-name"
     "write if x?, and in the block it is what it holds; to name what it holds, \
-     write if x? as g";
+     write if x as g";
   reads "x? is a test" "y = f(x)? and not z.w?" "(set y (and (? (f x)) (not (? (.w z)))))";
   reads "e? as g" "if f(x)? as g\n  g\nelif y? as h\n  h\nelse\n  0"
-    "(if-let [g (f x)] g (if-let [h y] h 0))";
-  reads "one-line e? as g" "v = if y? as h then h else 0" "(set v (if-let [h y] h 0))";
+    "(cond (as g (f x)) g (as h y) h :else 0)";
+  reads "one-line e? as g" "v = if y? as h then h else 0" "(set v (if (as h y) h 0))";
   reads "while e? as g" "while pop(s)? as x\n  f(x)"
-    "(while true (if-let [x (pop s)] (do (f x)) (break)))";
-  refuses "as after no test" "if x as y\n  y" "indent/as-test" "Write x? as name";
+    "(while true (if (as x (pop s)) (do (f x)) (break)))";
+  (* Decision 136: e as g without the ?, and inside an and chain. *)
+  reads "e as g" "if f(x) as g\n  g" "(when (as g (f x)) g)";
+  reads "as in an and chain" "if a and f(x) as g and g > 1 and b\n  g"
+    "(when (and a (as g (f x)) (> g 1) b) g)";
+  reads "two as in one chain" "v = if a as x and b? as y and x < y then x else y"
+    "(set v (if (and (as x a) (as y b) (< x y)) x y))";
+  reads "a kept when with as" "left = when get(grid, r + 1, c - 1) as g and is-empty-cell(g) then g"
+    "(set left (when (and (as g (get grid (+ r 1) (- c 1))) (is-empty-cell g)) g))";
+  reads "while as and" "while pop(s) as x and x > 0\n  f(x)"
+    "(while true (if (and (as x (pop s)) (> x 0)) (do (f x)) (break)))";
+  reads "elif as and" "if a\n  1\nelif f(x) as g and g > 1\n  g"
+    "(cond a 1 (and (as g (f x)) (> g 1)) g)";
+  refuses "as under or" "if a or f(x) as g\n  g" "indent/as-or" "Bind with as in an if of its own";
+  refuses "or after as" "if f(x) as g or b\n  g" "indent/as-or" "nothing to name";
+  refuses "or later in the chain" "if f(x) as g and a or b\n  g" "indent/as-or" "nothing to name";
+  refuses "as under not" "if not f(x) as g\n  g" "indent/as-not" "not turns the test around";
+  refuses "as after until" "until f(x) as g\n  g" "indent/as-until" "Write while";
+  refused "as-not-optional.fln" "fn main()\n  let n = 5\n  if n as g and g > 1\n    println(g)\n"
+    [ "n is i32, which always holds a value, so as has nothing to test";
+      "It is not a conversion" ];
+  refused "as-not-in-else.fln"
+    "fn f(o: i32?) -> i32\n  if o as g and g > 1\n    g\n  else\n    g\n\nfn main()\n  println(f(None))\n"
+    [ "unknown name g" ];
+  refused "as-not-in-elif.fln"
+    "fn f(o: i32?) -> i32\n  if o as g and g > 1\n    g\n  elif g > 0\n    1\n  else\n    0\n\nfn main()\n  println(f(None))\n"
+    [ "unknown name g" ];
+  refused "as-not-after.fln"
+    "fn f(o: i32?) -> i32\n  if o as g and g > 1\n    println(g)\n  g\n\nfn main()\n  println(f(None))\n"
+    [ "unknown name g" ];
   refused "present-i32.fln" "fn main()\n  let x = 5\n  println(x?)\n"
     [ "x is i32, which always holds a value, so x? has nothing to test";
       "a yes-or-no name starts with is- or has-, as in is-x" ];
   refused "narrowed-set.fln"
     "fn main()\n  let x: i32? = Some(1)\n  if x?\n    x = None\n  println(x ?? 0)\n"
     [ "x is tested with x? above, so in this block it is i32";
-      "while x? as item" ];
+      "while x as item" ];
   refused "not-narrowed-in-else.fln"
     "fn main()\n  let x: i32? = None\n  if x?\n    println(x + 1)\n  else\n    println(x + 1)\n"
     [ "Option(i32)" ];
@@ -1457,7 +1485,7 @@ let () =
   reads "a trailing ? tests the whole chain" "y = o?.i?"
     "(set y (? (?. [~o1 o] (.i ~o1))))";
   reads "and ? then as binds the chain's result" "if d?.k? as k\n  k"
-    "(if-let [k (?. [~o1 d] (.k ~o1))] k)";
+    "(when (as k (?. [~o1 d] (.k ~o1))) k)";
   refused "narrowed-param.fln"
     "fn f(x: i32?)\n  if x?\n    x += 100\n\nfn main()\n  f(Some(1))\n"
     [ "x is a parameter, and a parameter is not assignable" ];
@@ -1465,7 +1493,7 @@ let () =
     "fn main()\n  let x: i32? = Some(1)\n  if x?\n    x.n = 1\n"
     [ "so here it is what the Option holds, i32, and i32 has no fields" ];
   refuses "a chain is no place, and the fix is a test" "q?.x = 5" "indent/chain-assign"
-    "Test it first: if q?, and in the block q is what it holds, or if q? as g";
+    "Test it first: if q?, and in the block q is what it holds, or if q as g";
   refused "lowercase-type-arg.fln"
     "struct grain\n  w: i32\n\nfn main()\n  let v = vec-new(grain?)\n"
     [ "grain? here is the test that a value is present, and grain is a type";
@@ -1826,9 +1854,9 @@ let () =
   | _ -> fail "addr-taken-note.fln checked"
   | exception (Loc.Error d | Loc.Errors (d :: _)) ->
     if not (List.exists
-              (fun (n : Loc.note) -> Test_support.contains n.Loc.nmsg "Write if x? as g")
+              (fun (n : Loc.note) -> Test_support.contains n.Loc.nmsg "Write if x as g")
               d.Loc.notes)
-    then fail "addr-taken-note.fln: no note naming if x? as g on: %s" d.Loc.dmsg
+    then fail "addr-taken-note.fln: no note naming if x as g on: %s" d.Loc.dmsg
   | exception e -> fail "addr-taken-note.fln: %s" (diag_text e)
 
 let () = Test_support.report ~label:"syntax" ()