Handle 'return' errors.

* gash/built-ins/utils.scm (string->exit-status): New procedure.
* gash/built-ins/return.scm (main): Use it to simplify argument
checking; check for too many arguments; and print messages on
errors.
* tests/functions.org (Too many arguments to return): New test.

gash/built-ins/return.scm

@@ -17,8 +17,10 @@
 ;;; along with Gash.  If not, see <http://www.gnu.org/licenses/>.
 
 (define-module (gash built-ins return)
+  #:use-module (gash built-ins utils)
   #:use-module (gash compat)
-  #:use-module (gash environment))
+  #:use-module (gash environment)
+  #:use-module (ice-9 match))
 
 ;;; Commentary:
 ;;;
@@ -27,16 +29,14 @@
 ;;; Code:
 
 (define (main . args)
-  (let* ((arg (or (and (pair? args)
-                       (car (last-pair args)))
-                  (number->string (get-status))
-                  "0"))
-         (number (string->number arg))
-         (status (or (and (exact-integer? number)
-                          (>= number 0)
-                          (<= number 256)
-                          number)
-                     ;; If the above is not true, the exit status is
-                     ;; undefined.
-                     EXIT_FAILURE)))
-    (sh:return status)))
+  (match args
+    (() (main (number->string (get-status))))
+    ((arg)
+     (match (string->exit-status arg)
+       (#f (format (current-error-port)
+                   "gash: return: argument must be a number from 0 to 255~%")
+           EXIT_FAILURE)
+       (n (sh:return n))))
+    (_ (format (current-error-port)
+               "gash: return: too many arguments~%")
+       EXIT_FAILURE)))

gash/built-ins/utils.scm

@@ -21,7 +21,8 @@
   #:export (get-evaluator
             built-in?
             split-assignment
-            string->positive-integer))
+            string->positive-integer
+            string->exit-status))
 
 ;;; Commentary:
 ;;;
@@ -65,3 +66,11 @@
   (and=> (and (string-every char-set:ascii-digit s) (string->number s))
          (lambda (n)
            (and (exact-integer? n) (> n 0) n))))
+
+(define (string->exit-status s)
+  "Return the exit status represented by the string @var{s}.  If
+@var{s} does not represent an exit status (a decimal integer from 0 to
+255) return @code{#f}."
+  (and=> (and (string-every char-set:ascii-digit s) (string->number s))
+         (lambda (n)
+           (and (exact-integer? n) (>= n 0) (<= n 255) n))))

tests/functions.org

@@ -72,3 +72,14 @@
   cat $TEST_TMP/foo.tmp
   rm $TEST_TMP/foo.tmp
 #+end_src
+
+* Too many arguments to return
+:script:
+#+begin_src sh
+  foo () {
+      return 1 2 3
+  }
+  
+  foo
+#+end_src
+:status: 1