Add ability to read large lists

fitnesse/FitNesseRoot/RecentChanges.wiki

@@ -1,4 +1,4 @@
-|TranscendentalLisp.Recursion||17:56:26 Sat, Nov 18, 2017|
+|TranscendentalLisp.Recursion||10:47:58 Sun, Nov 19, 2017|
 |TranscendentalLisp||16:15:14 Fri, Mar 17, 2017|
 |TranscendentalLisp.Macros||10:10:15 Mon, Mar 13, 2017|
 |TranscendentalLisp.MacroTests||10:07:00 Mon, Mar 13, 2017|

fitnesse/FitNesseRoot/TranscendentalLisp/Recursion.wiki

@@ -4,8 +4,9 @@ Test
 Test recursion capabilities of various functions.
 
 | script                | lisp interpreter fixture                              |
+| show  | evaluate text | (load "lisp/random/big-list.lisp")                    |
 | show  | evaluate text | (load "lisp/random/list-builder.lisp")                |
-| check | evaluate text | (setq big-list (list-doubler '(1 1 1 1 1 1 1 1) 11))  | =~/1\)$/ |
+| check | evaluate text | big-list                                              | =~/1\)$/ |
 | check | evaluate text | (length big-list)                                     | 16384    |
 | check | evaluate text | (length (apply 'list big-list))                       | 16384    |
 | check | evaluate text | (apply '/ big-list)                                   | 1        |

src/token/RightParenthesis.java

@@ -1,11 +1,13 @@
 package token;
 
-import static sexpression.Nil.NIL;
+import static recursion.TailCalls.done;
 
 import java.util.function.Supplier;
 
 import error.LineColumnException;
 import file.FilePosition;
+import recursion.TailCall;
+import sexpression.Cons;
 import sexpression.SExpression;
 
 public class RightParenthesis extends Token {
@@ -20,8 +22,8 @@ public class RightParenthesis extends Token {
     }
 
     @Override
-    public SExpression parseSExpressionTail(Supplier<Token> getNextToken) {
-        return NIL;
+    public TailCall<SExpression> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
+        return done(accumulator);
     }
 
     public static class StartsWithRightParenthesisException extends LineColumnException {

src/token/Token.java

@@ -1,8 +1,13 @@
 package token;
 
+import static recursion.TailCalls.done;
+import static recursion.TailCalls.tailCall;
+import static sexpression.Nil.NIL;
+
 import java.util.function.Supplier;
 
 import file.FilePosition;
+import recursion.TailCall;
 import sexpression.Cons;
 import sexpression.SExpression;
 
@@ -24,19 +29,38 @@ public abstract class Token {
         return position;
     }
 
-    // s-expression ::= NUMBER | IDENTIFIER | STRING | QUOTE_MARK s-expression | LEFT_PAREN
+    // --------------------------------------------------------------------------------------------
+    // s-expression
+    // ::= NUMBER | IDENTIFIER | STRING | QUOTE_MARK s-expression | LEFT_PAREN s-expression-tail
+    //
     // s-expression-tail
-    // s-expression-tail ::= RIGHT_PAREN | s-expression s-expression-tail
+    // ::= RIGHT_PAREN | s-expression s-expression-tail
+    // --------------------------------------------------------------------------------------------
 
     public abstract SExpression parseSExpression(Supplier<Token> getNextToken);
 
     public SExpression parseSExpressionTail(Supplier<Token> getNextToken) {
-        SExpression first = parseSExpression(getNextToken);
+        Cons list = (Cons) parseListBackwards(NIL, getNextToken).invoke();
 
-        Token nextToken = getNextToken.get();
-        SExpression rest = nextToken.parseSExpressionTail(getNextToken);
+        return reverse(NIL, list).invoke();
+    }
 
-        return new Cons(first, rest);
+    public TailCall<SExpression> parseListBackwards(Cons accumulator, Supplier<Token> getNextToken) {
+        Cons nextAccumulator = new Cons(parseSExpression(getNextToken), accumulator);
+        Token next = getNextToken.get();
+
+        return tailCall(() -> next.parseListBackwards(nextAccumulator, getNextToken));
+    }
+
+    // TODO - refactor into a built in function?
+    private TailCall<SExpression> reverse(Cons accumulator, Cons list) {
+        if (list.isNull())
+            return done(accumulator);
+
+        Cons nextAccumulator = new Cons(list.getFirst(), accumulator);
+        Cons rest = (Cons) list.getRest();
+
+        return tailCall(() -> reverse(nextAccumulator, rest));
     }
 
 }