apl: ⍎ execute — eval string as APL source (+8)

- apl-execute: reassemble char-vector ravel into single string,
  then apl-run; handles plain string, scalar, and char-vector
- nested ⍎ ⍎ works; ⋄ separator threads through
- pipeline 148/148

lib/apl/transpile.sx

@@ -48,6 +48,7 @@
       ((= g "⎕←") apl-quad-print)
       ((= g "⍸") apl-where)
       ((= g "∪") apl-unique)
+      ((= g "⍎") apl-execute)
       (else (error "no monadic fn for glyph")))))
 
 (define
@@ -574,3 +575,11 @@
 (define apl-run (fn (src) (apl-eval-ast (parse-apl src) {})))
 
 (define apl-run-file (fn (path) (apl-run (file-read path))))
+
+(define
+  apl-execute
+  (fn
+    (arr)
+    (let
+      ((src (cond ((string? arr) arr) ((scalar? arr) (disclose arr)) (else (reduce str "" (get arr :ravel))))))
+      (apl-run src))))