apl: inline assignment a ← rhs mid-expression (+5 tests)

Parser: :name clause now detects 'name ← rhs' patterns inside
expressions. When seen, consumes the remaining tokens as RHS,
parses recursively, and emits a (:assign-expr name parsed-rhs)
value segment.

Eval-ast :dyad and :monad: when the right operand is an
:assign-expr node, capture the binding into env before
evaluating the left operand.  This realises the primes idiom:

  apl-run "(2 = +⌿ 0 = a ∘.| a) / a ← ⍳ 30"
  → 2 3 5 7 11 13 17 19 23 29

Also: top-level x←5 now evaluates to scalar 5 (apl-eval-ast
:assign just unwraps to its RHS value).

Caveat: ⍵-rebinding (the original primes.apl uses
'⍵←⍳⍵') is a :glyph-token; only :name-tokens are handled.
A regular variable name (like 'a') works.

lib/apl/transpile.sx

@@ -134,7 +134,11 @@
             (if
               (and (= (first fn-node) :fn-glyph) (= (nth fn-node 1) "∇"))
               (apl-call-dfn-m (get env "nabla") (apl-eval-ast arg env))
-              ((apl-resolve-monadic fn-node env) (apl-eval-ast arg env)))))
+              (let
+                ((arg-val (apl-eval-ast arg env)))
+                (let
+                  ((new-env (if (and (list? arg) (> (len arg) 0) (= (first arg) :assign-expr)) (assoc env (nth arg 1) arg-val) env)))
+                  ((apl-resolve-monadic fn-node new-env) arg-val))))))
         ((= tag :dyad)
           (let
             ((fn-node (nth node 1))
@@ -146,9 +150,13 @@
                 (get env "nabla")
                 (apl-eval-ast lhs env)
                 (apl-eval-ast rhs env))
-              ((apl-resolve-dyadic fn-node env)
-                (apl-eval-ast lhs env)
-                (apl-eval-ast rhs env)))))
+              (let
+                ((rhs-val (apl-eval-ast rhs env)))
+                (let
+                  ((new-env (if (and (list? rhs) (> (len rhs) 0) (= (first rhs) :assign-expr)) (assoc env (nth rhs 1) rhs-val) env)))
+                  ((apl-resolve-dyadic fn-node new-env)
+                    (apl-eval-ast lhs new-env)
+                    rhs-val))))))
         ((= tag :program) (apl-eval-stmts (rest node) env))
         ((= tag :dfn) node)
         ((= tag :bracket)
@@ -161,6 +169,8 @@
                     (fn (a) (if (= a :all) nil (apl-eval-ast a env)))
                     axis-exprs)))
               (apl-bracket-multi axes arr))))
+        ((= tag :assign-expr) (apl-eval-ast (nth node 2) env))
+        ((= tag :assign) (apl-eval-ast (nth node 2) env))
         (else (error (list "apl-eval-ast: unknown node tag" tag node)))))))
 
 (define