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beautiful-racket-demo/basic-demo-2/go.rkt

@@ -10,37 +10,43 @@
 (define return-ccs empty)
 
 (define (b-gosub num-expr)
-  (let/cc here-cc
-    (push! return-ccs here-cc)
+  (let/cc this-cc
+    (push! return-ccs this-cc)
     (b-goto num-expr)))
 
 (define (b-return)
-  (unless (pair? return-ccs)
+  (unless (not (empty? return-ccs))
     (raise-line-error "return without gosub"))
-  (define top-return-cc (pop! return-ccs))
-  (top-return-cc (void)))
+  (define top-cc (pop! return-ccs))
+  (top-cc (void)))
 
-(define thunk-table (make-hasheq))
+(define next-funcs (make-hasheq))
 
 (define-macro-cases b-for
   [(_ LOOP-ID START END) #'(b-for LOOP-ID START END 1)]
   [(_ LOOP-ID START END STEP)
-   #'(b-let LOOP-ID (let/cc loop-cc
-                      (hash-set! thunk-table
-                                 'LOOP-ID
-                                 (λ ()
-                                   (define next-val (+ LOOP-ID STEP))
-                                   (if (next-val . in-closed-interval? . START END)
-                                       (loop-cc next-val)
-                                       (hash-remove! thunk-table 'LOOP-ID))))
-                      START))])
+   #'(b-let LOOP-ID
+            (let/cc loop-cc
+              (hash-set! next-funcs
+                         'LOOP-ID
+                         (λ ()
+                           (define next-val
+                             (+ LOOP-ID STEP))
+                           (if (next-val
+                                . in-closed-interval? .
+                                START END)
+                               (loop-cc next-val)
+                               (hash-remove! next-funcs
+                                             'LOOP-ID))))
+              START))])
 
 (define (in-closed-interval? x start end)
   ((if (< start end) <= >=) start x end))
 
 (define-macro (b-next LOOP-ID)
   #'(begin
-      (unless (hash-has-key? thunk-table 'LOOP-ID)
-        (raise-line-error "next without for"))
-      (define thunk (hash-ref thunk-table 'LOOP-ID))
-      (thunk)))
+      (unless (hash-has-key? next-funcs 'LOOP-ID)
+        (raise-line-error
+         (format "`next ~a` without for" 'LOOP-ID)))
+      (define func (hash-ref next-funcs 'LOOP-ID))
+      (func)))

beautiful-racket-demo/basic-demo-2/parser.rkt

@@ -19,8 +19,7 @@ b-input : /"input" b-id
 b-gosub : /"gosub" b-expr
 b-return : /"return"
 b-for : /"for" b-id /"=" b-expr /"to" b-expr [/"step" b-expr]
-b-next : /"next" [b-id]
-
+b-next : /"next" b-id
 b-expr : b-or-expr
 b-or-expr : [b-or-expr "or"] b-and-expr
 b-and-expr : [b-and-expr "and"] b-not-expr
@@ -30,6 +29,5 @@ b-sum : [b-sum ("+"|"-")] b-product
 b-product : [b-product ("*"|"/"|"mod")] b-neg
 b-neg : ["-"] b-expt
 b-expt : [b-expt ("^")] b-value
-
 @b-value : b-number | b-id | /"(" b-expr /")"
 @b-number : INTEGER | DECIMAL