Add variable-prefix enumerator

pkgs/redex-pkgs/redex-lib/redex/private/enum.rkt

@@ -102,8 +102,16 @@
      [`(variable-except ,s ...)
       (apply except/e var/e s)]
      [`(variable-prefix ,s)
-      ;; todo
+      (define as-str (symbol->string s))
-      (unimplemented "var-prefix")]
+      (map/e (compose string->symbol
+                      (curry string-append as-str)
+                      symbol->string)
+             (compose string->symbol
+                      list->string
+                      (curry (flip drop) (string-length as-str))
+                      string->list
+                      symbol->string)
+             var/e)]
      [`variable-not-otherwise-mentioned
       unused/e]
      [`hole
@@ -323,3 +331,7 @@
             (disj-sum/e #:alternate? #t
                         (cons base/e (negate pair?))
                         (cons (cons/e any/e any/e) pair?)))))
+
+(define (flip f)
+  (λ (x y)
+     (f y x)))

pkgs/redex-pkgs/redex-test/redex/tests/enum-test.rkt

@@ -101,17 +101,21 @@
   (n (p_!_1 p_!_1))
   (x number))
 ;; Mismatch isn't working for now, will come back to this.
-#;#;#;
-(try-it 100 M m)
-(try-it 100 M n)
-(try-it 100 M p)
 
-;; test variable-not-otherwise-mentioned
+;; (try-it 100 M m)
-(define-language VarMentioned
+;; (try-it 100 M n)
+;; (try-it 100 M p)
+
+;; test variable filtering
+(define-language Vars
   (mention a b c x y z 2 #f #\c (vec 1 2))
-  (var variable-not-otherwise-mentioned))
+  (varpre (variable-prefix moo))
+  (varexc (variable-except x λ))
+  (varnom variable-not-otherwise-mentioned))
 
-(try-it 20 VarMentioned var)
+(try-it 100 Vars varpre)
+(try-it 100 Vars varexc)
+(try-it 100 Vars varnom)
 
 ;; Named repeats
 (define-language NRep