compat: Add 'thunk?' for Mes.

* gash/compat.scm [mes] (thunk?): New procedure.

gash/compat.scm

@@ -99,7 +99,8 @@
           flush-all-ports
           file-port?
           input-port?
-          output-port?)
+          output-port?
+          thunk?)
 
   (define-macro (define-inlinable . rest)
     `(define ,@rest))
@@ -172,4 +173,9 @@
   (let ((mes/dup dup))
     (define* (guile/dup fd #:optional new)
       (if new (dup2 fd new) (mes/dup fd)))
-    (set! dup guile/dup)))
+    (set! dup guile/dup))
+
+  (define (thunk? obj)
+    (and (closure? obj)
+         (let ((args (cadr (core:cdr obj))))
+           (or (null? args) (symbol? args))))))