read a var's type as a type, not as a call

`walk-parts' walked the whole `var' form, and a `fn' type's parameter
list is shaped like a call: `(fn ((c int)) int)' came out as
`int (*fp)(c int)'. A closure literal had no type, so calling one in
place missed the rewrite; sextest fed sexc symbols Sex cannot read.

tools/sextest/sextest.scm

@@ -86,8 +86,14 @@
         (compiled-file (create-temporary-file)))
     ;; `process' returns one record; `process-input-port' is named from
     ;; the child's side, so it is the port we write to.
+    ;;
+    ;; Sex has no symbol escaping -- `|' is an operator there, not a
+    ;; quote -- so the forms go out the way they were written. Left to
+    ;; escape, `||' would leave here as `|\|\||' and reach sexc as a
+    ;; different symbol.
     (let* ((proc (process compiler (append (list "-o" compiled-file) flags)))
            (sexc-stdin (process-input-port proc)))
+      (symbol-escape #f)
       (with-output-to-port sexc-stdin
         (fn (map (fn (fmt #t x)) src)))
       (close-output-port sexc-stdin)