Updated.

07-bae/main.rkt

@@ -1,4 +1,4 @@
-#lang pl 04
+#lang pl
 
 ; I added functions.
 
@@ -85,16 +85,28 @@
        [else (error 'parse-sexpr "bad `with' syntax in ~s" sexpr)])]
     [(list 'if p b a) (If (parse-sexpr p) (parse-sexpr b) (parse-sexpr a))]
     [(list 'if p 'then b 'else a) (If (parse-sexpr p) (parse-sexpr b) (parse-sexpr a))]
-    [(list 'and a b) (If (parse-sexpr a) (If (parse-sexpr b) pt pf) pf)]
-    [(list a 'and b) (If (parse-sexpr a) (If (parse-sexpr b) pt pf) pf)]
-    [(list 'or a b) (If (parse-sexpr a) pt (If (parse-sexpr b) pt pf))]
-    [(list a 'or b) (If (parse-sexpr a) pt (If (parse-sexpr b) pt pf))]
-    [(list 'not a) (If (parse-sexpr a) pf pt)]
+    [(list 'and a b) (andhelper a b)]
+    [(list a 'and b) (andhelper a b)]
+    [(list 'or a b) (orhelper a b)]
+    [(list a 'or b) (orhelper a b)]
+    [(list 'not a) (nothelper a)]
     [(list 'lambda (symbol: arg) body) (Lambda arg (parse-sexpr body))]
     [(list f 'of arg) (Call (parse-sexpr f) (parse-sexpr arg))]
     [(symbol: name) (Id name)]
     [else (error 'parse-sexpr "bad syntax in ~s" sexpr)]))
 
+(: andhelper : Sexpr Sexpr -> BAE)
+(define (andhelper a b)
+  (If (parse-sexpr a) (If (parse-sexpr b) pt pf) pf))
+
+(: orhelper : Sexpr Sexpr -> BAE)
+(define (orhelper a b)
+  (If (parse-sexpr a) pt (If (parse-sexpr b) pt pf)))
+
+(: nothelper : Sexpr -> BAE)
+(define (nothelper a )
+  (If (parse-sexpr a) pf pt))
+
 (: parse : String -> BAE)
 ;; parses a string containing an BAE expression to an BAE AST
 (define (parse str)
@@ -169,25 +181,19 @@
 (: eval-sum : (Listof BAE) -> Number)
 ; Evaluates a Sum expression.
 (define (eval-sum args)
-  (define l (length args))
-  (cond [(= l 0) 0]
-        [(= l 1) (eval-number (first args))]
-        [else (+ (eval-number (first args)) (eval-sum (rest args)))]))
+  (foldr + 0 (map eval-number args)))
 
 (: eval-mul : (Listof BAE) -> Number)
 ; Evaluates a Mul expression.
 (define (eval-mul args)
-  (define l (length args))
-  (cond [(= l 0) 1]
-        [(= l 1) (eval-number (first args))]
-        [else (* (eval-number (first args)) (eval-mul (rest args)))]))
+  (foldr * 1 (map eval-number args)))
 
 (: eval-sub : BAE (Listof BAE) -> Number)
 ; Evaluates a Sub expression.
 (define (eval-sub fst args)
   (define l (length args))
   (cond [(= l 0) (- (eval-number fst))]
-        [else (- (eval-number fst) (eval-sum args))])) ; Huh.
+        [else (- (eval-number fst) (eval-sum args))]))
 
 (: eval-div : BAE (Listof BAE) -> Number)
 ; Evaluates a Div expression.