Allow for tail calls in recurse argument list

lisp/lang/functions.lisp

@@ -10,10 +10,28 @@
    (t (cons (funcall function-name the-list)
        (maplist function-name (rest the-list))))))
 
-(defun append (listA listB)
-  (cond
-   ((null listA) listB)
-   (t (cons (first listA) (append (rest listA) listB)))))
+(defun append (list-one list-two)
+  (append-tail (reverse list-one) list-two))
+
+(defun append-tail (reversed-list list-two)
+  (if (null reversed-list) list-two
+    (recur (rest reversed-list) (cons (car reversed-list) list-two))))
+
+(defun reverse (the-list)
+  (reverse-tail () the-list))
+
+(defun reverse-tail (accumulator the-list)
+  (if (null the-list) accumulator
+    (recur (cons (first the-list) accumulator) (rest the-list))))
+
+(defun deep-reverse (the-list)
+  (if the-list
+    (append
+      (deep-reverse (rest the-list))
+      (list
+        (if (listp (first the-list))
+          (deep-reverse (first the-list))
+          (first the-list))))))
 
 (defun nth (n listA)
   (cond

lisp/lang/reverse.lisp

@@ -1,16 +0,0 @@
-(load "functions.lisp")
-
-(defun reverse (the-list)
-  (if the-list
-    (append
-      (reverse (rest the-list))
-      (list (first the-list)))))
-
-(defun deep-reverse (the-list)
-  (if the-list
-    (append
-      (deep-reverse (rest the-list))
-      (list
-        (if (listp (first the-list))
-          (deep-reverse (first the-list))
-          (first the-list))))))

lisp/random/list-builder.lisp

@@ -0,0 +1,5 @@
+(load "../lang/functions.lisp")
+
+(defun list-doubler (seed times-to-double)
+  (if (< times-to-double 1) seed
+   (recur (append seed seed) (- times-to-double 1))))

src/function/builtin/special/RECUR.java

@@ -32,11 +32,11 @@ public class RECUR extends LispSpecialFunction {
     }
 
     private void verifyValidRecurCall() {
-        if (executionContext.isRecurInitializing())
-            throw new NestedRecurException();
-
         if (!executionContext.isInFunctionCall())
             throw new RecurOutsideOfFunctionException();
+
+        if (executionContext.isRecurInitializing())
+            throw new NestedRecurException();
     }
 
     private Cons getRecurArguments(Cons argumentList) {

src/table/ExecutionContext.java

@@ -14,15 +14,17 @@ public class ExecutionContext {
     }
 
     private SymbolTable scope;
-    private Stack<LispFunction> functionCalls;
-    private boolean recurInitializing;
+    private Stack<LispFunctionRecurInfo> functionCalls;
     private boolean recur;
 
     private ExecutionContext() {
+        clearContext();
+    }
+
+    public void clearContext() {
         this.scope = new SymbolTable();
         this.functionCalls = new Stack<>();
         this.clearRecur();
-        this.clearRecurInitializing();
     }
 
     public SymbolTable getScope() {
@@ -38,13 +40,6 @@ public class ExecutionContext {
             scope = scope.getParent();
     }
 
-    public void clearContext() {
-        this.scope = new SymbolTable();
-        this.functionCalls = new Stack<>();
-        this.clearRecur();
-        this.clearRecurInitializing();
-    }
-
     public SExpression lookupSymbolValue(String symbolName) {
         for (SymbolTable t = scope; t != null; t = t.getParent())
             if (t.contains(symbolName))
@@ -54,7 +49,7 @@ public class ExecutionContext {
     }
 
     public void pushFunctionCall(LispFunction function) {
-        functionCalls.push(function);
+        functionCalls.push(new LispFunctionRecurInfo(function));
     }
 
     public void popFunctionCall() {
@@ -66,7 +61,7 @@ public class ExecutionContext {
     }
 
     public LispFunction getCurrentFunction() {
-        return functionCalls.peek();
+        return functionCalls.peek().getLispFunction();
     }
 
     public boolean isRecur() {
@@ -82,14 +77,41 @@ public class ExecutionContext {
     }
 
     public boolean isRecurInitializing() {
-        return recurInitializing;
+        return functionCalls.peek().isRecurInitializing();
     }
 
     public void setRecurInitializing() {
-        recurInitializing = true;
+        functionCalls.peek().setRecurInitializing();
     }
 
     public void clearRecurInitializing() {
-        recurInitializing = false;
+        functionCalls.peek().clearRecurInitializing();
+    }
+
+    public static class LispFunctionRecurInfo {
+
+        private LispFunction lispFunction;
+        private boolean recurInitializing;
+
+        public LispFunctionRecurInfo(LispFunction lispFunction) {
+            this.lispFunction = lispFunction;
+            this.clearRecurInitializing();
+        }
+
+        public boolean isRecurInitializing() {
+            return recurInitializing;
+        }
+
+        public void setRecurInitializing() {
+            this.recurInitializing = true;
+        }
+
+        public void clearRecurInitializing() {
+            this.recurInitializing = false;
+        }
+
+        public LispFunction getLispFunction() {
+            return lispFunction;
+        }
     }
 }

test/function/builtin/special/RECURTest.java

@@ -166,6 +166,13 @@ public class RECURTest extends SymbolAndFunctionCleaner {
         assertSExpressionsMatch(parseString("PASS"), evaluateString("(nested-tail)"));
     }
 
+    @Test
+    public void recurWithNestedTailRecursiveFunction() {
+        evaluateString("(defun one (n) (if (= n  0) 0 (recur (- n 1))))");
+        evaluateString("(defun two (n) (if (= n  0) 'PASS (recur (one n))))");
+        assertSExpressionsMatch(parseString("PASS"), evaluateString("(two 20)"));
+    }
+
     @Test
     public void nestedRecurException_HasCorrectAttributes() {
         assertIsErrorWithMessage(new NestedRecurException());