Add more helper functions for the stepping relation

semantics.rkt

@@ -46,11 +46,18 @@
 (define (update-stats f mstate)
   (struct-copy State mstate [stats (f (State-stats mstate))]))
 
+(: update-stack (-> (-> Stack Stack) State State))
+(define (update-stack f mstate)
+  (struct-copy State mstate [stack (f (State-stack mstate))]))
+
 (: allocate-node (-> Heap Node (Values Heap Addr)))
 (define (allocate-node heap node)
   (let ([addr (new-addr)])
     (values (hash-set heap addr node) addr)))
 
+(: lookup-node (-> Heap Addr Node))
+(define lookup-node hash-ref)
+
 (: initialize-heap (-> (Listof CoreScDefn) (Values Heap Globals)))
 (define (initialize-heap scs)
   (for/fold ([heap : Heap empty-heap]
@@ -62,5 +69,36 @@
 
 (: compile-core (-> (Listof CoreScDefn) State))
 (define (compile-core scdefs)
-  (let-values ([(heap globals) (initialize-heap scdefs)])
+  (let-values ([(heap globals) (initialize-heap (append scdefs prelude))])
     (State empty-stack empty-dump heap globals empty-stats)))
+
+
+(: data-node? (-> Node Boolean))
+(define data-node? integer?)
+
+(: final-state? (-> State Boolean))
+(define (final-state? st)
+  (match (State-stack st)
+    [(list n) (data-node? (lookup-node (State-heap st) n))]
+    [_ #f]))
+
+(: step (-> State State))
+(define (step state)
+  (let ([stack (State-stack state)])
+    (match stack
+      [(cons addr _)
+       (step-node state (lookup-node (State-heap state) addr))]
+      ['() (error "Invalid state")])))
+
+(: step-node (-> State Node State))
+(define (step-node st n)
+  (match n
+    [(? integer?) (error "A number cannot be stepped any further!")]
+    [(list a _) (update-stack (λ (x) (cons a x)) st)]
+    [(list 'define (list name args ...) body)
+     (step-sc st name args body)]))
+
+(: step-sc (-> State Name (Listof Name) CoreExpr State))
+(define (step-sc state sc args body)
+
+  (error "to be implemented"))