Done with bang.

13-bang/main.rkt

@@ -207,11 +207,13 @@
      (FunV names bound-body #t env)]
     [(Call fun-expr arg-exprs)
      (let ([fval (eval* fun-expr)]
-           [arg-vals (map eval* arg-exprs)])
+           [arg-vals-thunk (lambda () (map eval* arg-exprs))]) ;THunk.
        (cases fval
-         [(PrimV proc) (proc arg-vals)]
+         [(PrimV proc) (proc (arg-vals-thunk))]
          [(FunV names body ref? fun-env)
-          (if ref? (eval-rfun names arg-exprs body fun-env) (eval-body body (extend names arg-vals fun-env)))]
+          (if ref?
+              (eval-rfun names arg-exprs body env fun-env)
+              (eval-body body (extend names (arg-vals-thunk) fun-env)))]
          [else (error 'eval "function call with a non-function: ~s"
                       fval)]))]
     [(If cond-expr then-expr else-expr)
@@ -224,9 +226,9 @@
      (set-box! (lookup thing env) (eval* as)) ; We are not a lazy language.
      (VoidV)]))
 
-(: eval-rfun : (Listof Symbol) (Listof TOY) (Listof TOY) ENV -> VAL)
+(: eval-rfun : (Listof Symbol) (Listof TOY) (Listof TOY) ENV ENV -> VAL)
-(define (eval-rfun params args body env)
+(define (eval-rfun params args body callerenv calleeenv)
-  (eval-body body (raw-extend params (get-boxes args env) env)))
+  (eval-body body (raw-extend params (get-boxes args callerenv) calleeenv)))
 
 (: get-boxes : (Listof TOY) ENV -> (Listof (Boxof VAL)))
 (define (get-boxes ids env)
@@ -254,6 +256,8 @@
 
 ;;; ----------------------------------------------------------------
 ;;; Tests
+(test (run "{{rfun {x} x} {/ 4 0}}") =error> "non-identifier")
+(test (run "{5 {/ 6 0}}") =error> "non-function")
 (test (run "
 {bind
     {
@@ -274,8 +278,7 @@
     {swap! a b}
 
     {+ a {* 10 b}}
-}
+}") => 12)
-") => 12)
 
 (test (run "{bind {{make-counter
 {fun {}
@@ -338,11 +341,11 @@ c}}}}}
 
 ;; More tests for complete coverage
 (test (run "{bind x 5 x}")      =error> "bad `bind' syntax")
-(test (run "{fun x x}")         =error> "bad `fun' syntax")
+(test (run "{fun x x}")         =error> "parse-sexpr: bad function syntax in (fun x x)")
 (test (run "{if x}")            =error> "bad `if' syntax")
 (test (run "{}")                =error> "bad syntax")
-(test (run "{bind {{x 5} {x 5}} x}") =error> "duplicate*bind*names")
+(test (run "{bind {{x 5} {x 5}} x}") =error> "parse-sexpr: duplicate `bind' names: (x x)")
-(test (run "{fun {x x} x}")     =error> "duplicate*fun*names")
+(test (run "{fun {x x} x}")     =error> "parse-sexpr: bad parameters defined for function in (fun (x x) x)")
 (test (run "{+ x 1}")           =error> "no binding for")
 (test (run "{+ 1 {fun {x} x}}") =error> "bad input")
 (test (run "{+ 1 {fun {x} x}}") =error> "bad input")