compat: More shims for Mes.

* gash/compat.scm [mes] (call-with-input-file): New procedure.
[mes] (exact?): New procedure.
[mes] (set-program-arguments): New procedure.
[mes] (open-file): New procedure.
[mes] (false-if-exception): New syntax.
[mes] (hex-digits): New variable.
[mes] (char->hex-string): New procedure.
[mes] (make-random-file-name): New procedure.
[mes] (tmpfile): New procedure.

gash/compat.scm

@@ -103,11 +103,16 @@
           file-port?
           input-port?
           output-port?
+          call-with-input-file
           call-with-input-string
           thunk?
           EXIT_SUCCESS
           EXIT_FAILURE
+          exact?
           exact-integer?
+          set-program-arguments
+          open-file
+          tmpfile
           sort)
 
   (define-macro (define-inlinable . rest)
@@ -220,6 +225,13 @@
   (define (input-port? port) #f)
   (define (output-port? port) #f)
 
+  (define (call-with-input-file file proc)
+    (let ((port (open-input-file file)))
+      (call-with-values (lambda () (proc port))
+        (lambda results
+          (close-port port)
+          (apply values results)))))
+
   (define (call-with-input-string str proc)
     (let ((port (open-input-string str)))
       (call-with-values (lambda () (proc port))
@@ -242,8 +254,55 @@
   (define EXIT_FAILURE 1)
 
   ;; Mes only has exact integers.
+  (define exact? integer?)
   (define exact-integer? integer?)
 
+  (define (set-program-arguments args)
+    (set! %argv args))
+
+  (define (open-file filename mode)
+    (cond
+     ((string=? mode "r") (open-input-file filename))
+     ((string=? mode "w") (open-output-file filename))
+     (else (error "Unsupported file mode" mode))))
+
+  ;; Because Mes is not careful when resolving syntax, this will
+  ;; shadow its built-in 'false-if-exception' shim even though we
+  ;; don't export it (which would result in a warning).
+  (define-syntax-rule (false-if-exception body1 body2 ...)
+    (catch #t
+      (lambda () body1 body2 ...)
+      (lambda _ #f)))
+
+  (define hex-digits "0123456789abcdef")
+
+  (define (char->hex-string c)
+    (define b (char->integer c))
+    (string (string-ref hex-digits (logand (ash b -4) #xf))
+            (string-ref hex-digits (logand b #xf))))
+
+  (define (make-random-file-name)
+    (let* ((p (open-input-file "/dev/urandom"))
+           (dir (or (getenv "TMPDIR") "/tmp"))
+           (name (string-append dir "/mes-tmp-"
+                                (char->hex-string (read-char p))
+                                (char->hex-string (read-char p))
+                                (char->hex-string (read-char p))
+                                (char->hex-string (read-char p)))))
+      (close-port p)
+      name))
+
+  (define (tmpfile)
+    (define flags (logior O_EXCL O_CREAT O_RDWR))
+    ;; XXX: Mes provides no way to check for EEXIST, so we can't loop
+    ;; to ensure we get a fresh name.  Hence, we cross our fingers and
+    ;; hope we don't crash because of a name collision.
+    (let* ((name (make-random-file-name))
+           (port (open name flags)))
+      ;; Delete the file so that it's gone when we're done.
+      (delete-file name)
+      port))
+
   ;; A simple (slow!) sort procedure.  It's needed for globbing.
   (define (sort items less)
     (define (split-reverse lst)