Finish 2 minus1k

Final/2.rkt

@@ -7,6 +7,7 @@
   [appE (fun-expr : Exp) (arg-expr : Exp)]
   [errorE (msg : String)] ;; New
   [if0E (test : Exp) (then : Exp) (else : Exp)]
+  [minus1E (n : Exp)]
   )
 
 (define-type Value
@@ -43,6 +44,7 @@
                 (k : Continuation)]
   [doMinusK (v1 : Value)
             (k : Continuation)]
+  [doMinus1K (k : Continuation)]
   [appArgK (arg-expr : Exp)
            (env : Env)
            (k : Continuation)]
@@ -77,8 +79,8 @@
          (lamE varE body))]
       [(s-exp-match? `(error STRING) sx) (errorE (s-exp->string (sx-ref sx 1)))]
       [(s-exp-match? `(error ANY) sx) (parse-error sx)]
-      [(s-exp-match? `(ANY ANY) sx)
-       (appE (px 0) (px 1))]
+      [(s-exp-match? `(-- ANY) sx) (minus1E (px 1))]
+      [(s-exp-match? `(ANY ANY) sx) (appE (px 0) (px 1))]
       [(s-exp-list? sx)
        (case (s-exp->symbol (sx-ref sx 0))
          [(+) (plusE (px 1) (px 2))]
@@ -113,7 +115,7 @@
      (interp fun-expr env (appArgK arg-expr env k))]
     [(if0E test-expr then-expr else-expr)
      (interp test-expr env (doIfK then-expr else-expr env k))]
-
+    [(minus1E n) (interp n env (doMinus1K k))]
     ))
 
 (define (continue [k : Continuation] [v : Value]) : Value
@@ -127,6 +129,8 @@
      (interp r env (doMinusK v next-k))]
     [(doMinusK v1 next-k)
      (continue next-k (arith-op - v1 v))]
+    [(doMinus1K next-k)
+     (continue next-k (arith-op - v (numV 1)))]
     [(appArgK arg-expr env next-k)
      (interp arg-expr env (doAppK v next-k))]
     [(doAppK fun-val next-k)
@@ -240,3 +244,36 @@
                       {body-proc {lam {x} {{fX fX} x}}}}}}})
         (errorV "reached zero"))
   )
+
+; unary decrement
+(module+ test
+  (test (parse `{-- 2}) (minus1E (numE 2))))
+
+(module+ test
+  (test (run `{-- 2}) (numV 1))
+  (test (run `{{lam {x} {-- x}} 3}) (numV 2))
+  (test (run `{{lam {y} {+ {-- y} {-- y}}} 10}) (numV 18))
+  (test (run `{{lam {f} {f 4}} {lam {x} {-- x}}}) (numV 3)))
+
+; multiplication
+(module+ test
+  (define fact-prog
+    `{{lam {mkrec}
+           {{lam {fact}
+                 ;; Call fact on 5:
+                 {fact 5}}
+            ;; Create recursive fact
+            {mkrec
+             {lam {fact}
+                  {lam {n}
+                       {if0 n
+                            1
+                            {* n {fact {-- n}}}}}}}}}
+      ;; mkrec:
+      {lam {body-proc}
+           {{lam {fX}
+                 {fX fX}}
+            {lam {fX}
+                 {body-proc {lam {x} {{fX fX} x}}}}}}})
+
+  (test (run fact-prog) (numV 120)))