The sketch's condition syntax, checked against the parser rather than recalled

handler-bind takes (Type [name] body ...) and has since it was written; the
sketch paired a type with an fn, which is the shape parse.ml names in its own
refusal message. load-level had two return types. And there is no defcondition
anywhere in the tree -- a condition type is an ordinary struct, which is what
both spec-conditions.md and conditions.org say, so the one form in this file that
introduced one was inventing it.

The header's rules went with them: lowercase-is-a-type-variable and "no sigils"
are both the pre-$t spelling, and let never took an annotation.

plan.org

@@ -194,8 +194,10 @@ and on a managed ~class~ instance. An ordinary ~struct~ never carries one.
 
 - Types are mandatory; *inference* makes them feel optional. Annotate function
   signatures, infer locals — Odin/Zig/Rust ergonomics.
-- Signatures are annotated as inline name/type pairs, as in ~let~ and
-  ~defstruct~: ~(defn area [s Shape] f32 ...)~. No separate ~declare~ form —
+- Signatures are annotated as inline name/type pairs, as in ~defstruct~ and a
+  ~restart-case~ clause: ~(defn area [s Shape] f32 ...)~. A ~let~ is not one of
+  them — a local is inferred from its initialiser and takes no annotation at
+  all. No separate ~declare~ form —
   ~declare~ is kept only where there is no body (forward declarations, FFI).
 - Annotations at function boundaries are unavoidable, because compile-time
   overloading is incompatible with full inference. Locals are inferred.

spec-memory.md

@@ -166,6 +166,12 @@ instead:
 (defn largest [xs [$t]  gt (Fn [$t $t] bool)] (Option $t) ...)
 ```
 
+The value handed to such a parameter is a named `defn`. An `fn` cannot be written
+inline into it, because the generic body is checked with nothing substituted and
+there is no concrete type yet for the `fn`'s own parameters to come from; that
+restriction lifts at a monomorphic call site, where `reduce`'s and `filter`'s
+callbacks are ordinary inline `fn`s.
+
 The alternatives to predicates — compile-time interfaces, or intrinsics
 restricted to primitives — remain deliberately deferred until the base checker is
 stable (build sequence milestone 4). The ceiling is that nobody can supply a

syntax-sketch.flan

@@ -2,11 +2,13 @@
 ;;
 ;; Rules held here:
 ;;   - every type notation reads as exactly ONE data item
-;;   - types are inline name/type pairs, as in `let` and `defstruct`
+;;   - types are inline name/type pairs, as in `defstruct` and a restart-case
+;;     clause. NOT in `let`: a local is inferred and takes no annotation
 ;;   - the return type is always written; () is unit, a real zero-sized type
 ;;     rather than C's void
-;;   - lowercase type names are variables, Capitalized are concrete
-;;   - no `!` convention (nothing is immutable), no `->`, no sigils
+;;   - a type VARIABLE is $t; every other type name is concrete, whatever its
+;;     case. Lowercase-is-a-variable was the first spelling and is gone
+;;   - no `!` convention (nothing is immutable), and no `->`
 ;;
 ;; Normative references: spec-memory.md (ownership, containers, places,
 ;; generics, function values) and spec-conditions.md (restart semantics).
@@ -91,8 +93,8 @@
 ;; >". Nor can an `fn` be written inline into a (Fn [$t $t] bool) argument: the
 ;; generic body is checked with nothing substituted, so there is no type for the
 ;; fn's own parameters to come from yet. Inside a generic the callback is a
-;; named defn; at a monomorphic call site the fn can be written where it is
-;; used, as `centroid` does below.
+;; named defn; at a monomorphic call site, where the types are already
+;; concrete, the fn can be written inline where it is used.
 
 ;; Parameters are immutable values; pass a pointer to mutate. `[Enemy]` is a
 ;; borrowed slice — centroid neither owns nor frees the storage.
@@ -151,7 +153,9 @@
 ;; load-texture cannot know the right recovery — an editor wants a placeholder,
 ;; a release build wants to abort, a hot-reload session wants to retry after the
 ;; file is fixed on disk. So it offers a menu and the caller chooses.
-(defcondition AssetMissing [path string])
+;; A condition type is an ordinary struct — there is no defcondition, and no
+;; class hierarchy to put one in. Matching is by type plus a predicate.
+(defstruct AssetMissing [path string])
 
 ;; `signal` has type () and RETURNS if every handler returns normally, so the
 ;; fall-through path of a restart-case in value position must still produce the
@@ -168,10 +172,14 @@
 
 ;; Intermediate frames say nothing about AssetMissing. Nothing to thread.
 ;; invoke-restart has type Never: it does not return to the handler.
-(defn load-level [path string] () Level
-  (handler-bind [AssetMissing (fn [c]
-                                (log "missing asset:" (.path c))
-                                (invoke-restart 'use-placeholder))]
+;; A handler clause is (Type [name] body ...) — the type, then the one binding,
+;; then the body. It is not a type paired with an `fn`, and a handler closes
+;; over nothing: it is lifted into its own function, so a value it wants to keep
+;; goes on the condition or into a global.
+(defn load-level [path string] Level
+  (handler-bind [(AssetMissing [c]
+                   (log "missing asset:" (.path c))
+                   (invoke-restart 'use-placeholder))]
     (parse-level (slurp path))))
 
 ;; A handler that returns normally does not unwind, so the signaller carries on.
@@ -189,10 +197,9 @@
 
 (defn collect-parse-errors [src string] (Result Ast)
   (let [errors (make-vec ParseError)]
-    (handler-bind [ParseError (fn [c]
-                                (push errors c)   ; value struct: copies out of
-                                                  ; the signalling frame
-                                (invoke-restart 'skip-form))]
+    (handler-bind [(ParseError [c]
+                     (push errors c)              ; value struct: copies out of
+                     (invoke-restart 'skip-form))] ; the signalling frame
       (let [ast (parse-all (parser src))]
         (if (zero? (len errors))
           (Ok ast)