Restore scope properly after errors

src/function/UserDefinedFunction.java

@@ -2,14 +2,14 @@ package function;
 
 import static function.builtin.EVAL.eval;
 import static java.text.MessageFormat.format;
-import static recursion.tail.TailCalls.done;
+import static recursion.TailCalls.done;
 import static sexpression.Nil.NIL;
 
 import java.util.ArrayList;
 
 import error.LispException;
-import recursion.tail.TailCall;
+import recursion.TailCall;
-import recursion.tail.TailCalls;
+import recursion.TailCalls;
 import sexpression.Cons;
 import sexpression.SExpression;
 import sexpression.Symbol;

src/function/builtin/EVAL.java

@@ -12,6 +12,7 @@ import error.LispException;
 import function.ArgumentValidator;
 import function.FunctionNames;
 import function.LispFunction;
+import function.builtin.special.RECUR.RecurNotInTailPositionException;
 import sexpression.BackquoteExpression;
 import sexpression.Cons;
 import sexpression.LambdaExpression;
@@ -22,10 +23,17 @@ import table.ExecutionContext;
 @FunctionNames({ "EVAL" })
 public class EVAL extends LispFunction {
 
+    private static ExecutionContext executionContext = ExecutionContext.getInstance();
+
     public static SExpression eval(SExpression sExpression) {
         Cons argumentList = makeList(sExpression);
 
-        return lookupFunction("EVAL").call(argumentList);
+        try {
+            return lookupFunction("EVAL").call(argumentList);
+        } catch (LispException e) {
+            executionContext.restoreGlobalScope();
+            throw e;
+        }
     }
 
     public static Cons evalRecurArgumentList(Cons argumentList) {
@@ -62,27 +70,28 @@ public class EVAL extends LispFunction {
     }
 
     private ArgumentValidator argumentValidator;
-    private ExecutionContext executionContext;
 
     public EVAL(String name) {
         this.argumentValidator = new ArgumentValidator(name);
         this.argumentValidator.setExactNumberOfArguments(1);
-        this.executionContext = ExecutionContext.getInstance();
     }
 
     @Override
     public SExpression call(Cons argumentList) {
-        if (executionContext.isRecur()) {
+        verifyNotRecurring();
-            executionContext.clearContext();
-            throw new RecurNotInTailPositionException();
-        }
-
         argumentValidator.validate(argumentList);
         SExpression argument = argumentList.getFirst();
 
         return evaluateExpression(argument);
     }
 
+    private void verifyNotRecurring() {
+        if (executionContext.isRecur()) {
+            executionContext.clearRecur();
+            throw new RecurNotInTailPositionException();
+        }
+    }
+
     private SExpression evaluateExpression(SExpression argument) {
         if (argument.isList())
             return evaluateList(argument);
@@ -123,10 +132,7 @@ public class EVAL extends LispFunction {
         if (function.isArgumentListEvaluated())
             argumentList = evaluateArgumentList(argumentList);
 
-        if (executionContext.isRecur()) {
+        verifyNotRecurring();
-            executionContext.clearContext();
-            throw new RecurNotInTailPositionException();
-        }
 
         SExpression result = function.call(argumentList);
 
@@ -211,14 +217,4 @@ public class EVAL extends LispFunction {
         }
     }
 
-    public static class RecurNotInTailPositionException extends LispException {
-
-        private static final long serialVersionUID = 1L;
-
-        @Override
-        public String getMessage() {
-            return "recur not in tail position";
-        }
-    }
-
 }

src/function/builtin/cons/LENGTH.java

@@ -1,15 +1,15 @@
 package function.builtin.cons;
 
 import static function.builtin.cons.LIST.makeList;
-import static recursion.tail.TailCalls.done;
+import static recursion.TailCalls.done;
-import static recursion.tail.TailCalls.tailCall;
+import static recursion.TailCalls.tailCall;
 
 import java.math.BigInteger;
 
 import function.ArgumentValidator;
 import function.FunctionNames;
 import function.LispFunction;
-import recursion.tail.TailCall;
+import recursion.TailCall;
 import sexpression.Cons;
 import sexpression.LispNumber;
 

src/function/builtin/special/RECUR.java

@@ -5,7 +5,6 @@ import static function.builtin.EVAL.evalRecurArgumentList;
 import error.LispException;
 import function.ArgumentValidator;
 import function.FunctionNames;
-import function.LispFunction;
 import function.LispSpecialFunction;
 import sexpression.Cons;
 import sexpression.SExpression;
@@ -31,23 +30,31 @@ public class RECUR extends LispSpecialFunction {
             throw new RecurOutsideOfFunctionException();
 
         argumentValidator.validate(argumentList);
-        LispFunction currentFunction = executionContext.getCurrentFunction();
+        Cons recurArguments = getRecurArguments(argumentList);
+        executionContext.setRecur();
+
+        return recurArguments;
+    }
+
+    private Cons getRecurArguments(Cons argumentList) {
         Cons recurArguments = argumentList;
 
-        executionContext.setRecurInitializing();
-
         try {
-            if (currentFunction.isArgumentListEvaluated())
+            executionContext.setRecurInitializing();
+
+            if (isRecurArgumentListEvaluated())
                 recurArguments = evalRecurArgumentList(argumentList);
         } finally {
             executionContext.clearRecurInitializing();
         }
 
-        executionContext.setRecur();
-
         return recurArguments;
     }
 
+    private boolean isRecurArgumentListEvaluated() {
+        return executionContext.getCurrentFunction().isArgumentListEvaluated();
+    }
+
     public static class RecurOutsideOfFunctionException extends LispException {
 
         private static final long serialVersionUID = 1L;
@@ -68,4 +75,14 @@ public class RECUR extends LispSpecialFunction {
         }
     }
 
+    public static class RecurNotInTailPositionException extends LispException {
+
+        private static final long serialVersionUID = 1L;
+
+        @Override
+        public String getMessage() {
+            return "recur not in tail position";
+        }
+    }
+
 }

src/recursion/TailCall.java

@@ -1,4 +1,4 @@
-package recursion.tail;
+package recursion;
 
 import java.util.stream.Stream;
 

src/recursion/TailCalls.java

@@ -1,4 +1,4 @@
-package recursion.tail;
+package recursion;
 
 public class TailCalls {
 

src/sexpression/Cons.java

@@ -1,9 +1,9 @@
 package sexpression;
 
-import static recursion.tail.TailCalls.done;
+import static recursion.TailCalls.done;
-import static recursion.tail.TailCalls.tailCall;
+import static recursion.TailCalls.tailCall;
 
-import recursion.tail.TailCall;
+import recursion.TailCall;
 
 @DisplayName("list")
 public class Cons extends SExpression {

src/table/ExecutionContext.java

@@ -33,6 +33,11 @@ public class ExecutionContext {
         this.scope = scope;
     }
 
+    public void restoreGlobalScope() {
+        while (!scope.isGlobal())
+            scope = scope.getParent();
+    }
+
     public void clearContext() {
         this.scope = new SymbolTable();
         this.functionCalls = new Stack<>();

test/function/builtin/EVALTest.java

@@ -2,6 +2,7 @@ package function.builtin;
 
 import static function.builtin.EVAL.lookupSymbol;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.fail;
 import static sexpression.Nil.NIL;
 import static testutil.TestUtilities.assertIsErrorWithMessage;
 import static testutil.TestUtilities.assertSExpressionsMatch;
@@ -18,6 +19,7 @@ import function.builtin.EVAL.UndefinedFunctionException;
 import function.builtin.EVAL.UndefinedSymbolException;
 import function.builtin.EVAL.UnmatchedAtSignException;
 import function.builtin.EVAL.UnmatchedCommaException;
+import function.builtin.special.RECUR.RecurNotInTailPositionException;
 import testutil.SymbolAndFunctionCleaner;
 
 public class EVALTest extends SymbolAndFunctionCleaner {
@@ -178,4 +180,50 @@ public class EVALTest extends SymbolAndFunctionCleaner {
         assertSExpressionsMatch(parseString("((1 2 3))"), evaluateString(input));
     }
 
+    @Test
+    public void scopeRestoredAfterFailure_Let() {
+        evaluateString("(setq n 100)");
+        try {
+            evaluateString("(let ((n 200)) (begin 1 2 3 y))");
+            fail("expected exception");
+        } catch (UndefinedSymbolException e) {}
+
+        assertSExpressionsMatch(parseString("100"), evaluateString("n"));
+    }
+
+    @Test
+    public void scopeRestoredAfterFailure_Defun() {
+        evaluateString("(setq n 100)");
+        try {
+            evaluateString("(defun test (n) (begin 1 2 3 y))");
+            evaluateString("(test 200)");
+            fail("expected exception");
+        } catch (UndefinedSymbolException e) {}
+
+        assertSExpressionsMatch(parseString("100"), evaluateString("n"));
+    }
+
+    @Test
+    public void scopeRestoredAfterFailure_Lambda() {
+        evaluateString("(setq n 100)");
+        try {
+            evaluateString("((lambda (n) (begin 1 2 3 y)) 200)");
+            fail("expected exception");
+        } catch (UndefinedSymbolException e) {}
+
+        assertSExpressionsMatch(parseString("100"), evaluateString("n"));
+    }
+
+    @Test
+    public void scopeRestoredAfterFailure_Recur() {
+        evaluateString("(setq n 100)");
+        try {
+            evaluateString("(defun tail-recursive (n) (begin (recur) 2))");
+            evaluateString("(tail-recursive 200)");
+            fail("expected exception");
+        } catch (RecurNotInTailPositionException e) {}
+
+        assertSExpressionsMatch(parseString("100"), evaluateString("n"));
+    }
+
 }

test/function/builtin/special/RECURTest.java

@@ -9,9 +9,10 @@ import org.junit.Test;
 
 import function.ArgumentValidator.BadArgumentTypeException;
 import function.ArgumentValidator.TooManyArgumentsException;
-import function.builtin.EVAL.RecurNotInTailPositionException;
 import function.builtin.special.RECUR.NestedRecurException;
+import function.builtin.special.RECUR.RecurNotInTailPositionException;
 import function.builtin.special.RECUR.RecurOutsideOfFunctionException;
+import sexpression.SExpression;
 import testutil.SymbolAndFunctionCleaner;
 
 public class RECURTest extends SymbolAndFunctionCleaner {
@@ -53,13 +54,13 @@ public class RECURTest extends SymbolAndFunctionCleaner {
     }
 
     @Test(expected = RecurNotInTailPositionException.class)
-    public void recurInNonTailPosition_ThrowsException() {
+    public void recurInNonTailPositionInArgumentList() {
         evaluateString("(defun tail-recursive (n) (if (= n  0) 'PASS (list (recur (- n 1)))))");
         evaluateString("(tail-recursive 900)");
     }
 
     @Test(expected = RecurNotInTailPositionException.class)
-    public void recurInNonTailPosition2_ThrowsException() {
+    public void recurInNonTailPositionInBegin() {
         evaluateString("(defun tail-recursive (n) (begin (recur) 2))");
         evaluateString("(tail-recursive 900)");
     }
@@ -76,6 +77,18 @@ public class RECURTest extends SymbolAndFunctionCleaner {
         assertSExpressionsMatch(parseString("PASS"), evaluateString("(tail-recursive 900)"));
     }
 
+    @Test
+    public void recurInTailPositionWithApply() {
+        evaluateString("(defun tail-recursive (n) (if (= n  0) 'PASS (apply 'recur (list (- n 1)))))");
+        assertSExpressionsMatch(parseString("PASS"), evaluateString("(tail-recursive 900)"));
+    }
+
+    @Test
+    public void recurInTailPositionWithFuncall() {
+        evaluateString("(defun tail-recursive (n) (if (= n  0) 'PASS (call 'recur (- n 1))))");
+        assertSExpressionsMatch(parseString("PASS"), evaluateString("(tail-recursive 900)"));
+    }
+
     @Test
     public void recurCallsCurrentFunction_WithApply() {
         evaluateString("(defun tail-recursive (n) (if (= n  0) 'PASS (recur (- n 1))))");
@@ -126,14 +139,24 @@ public class RECURTest extends SymbolAndFunctionCleaner {
 
         assertSExpressionsMatch(parseString("PASS"), evaluateString("(tail-recursive 900)"));
     }
-    // recur non-tail in apply call
 
-    // recur with no args, alters global variable
+    @Test
+    public void recurWithNoArgs_AltersGlobalVariable() {
+        evaluateString("(defun tail-recursive () (if (= n  0) 'PASS (begin (setq n (- n 1)) (recur))))");
+        evaluateString("(setq n 200)");
+        assertSExpressionsMatch(parseString("PASS"), evaluateString("(tail-recursive)"));
+    }
 
-    // recur with anonymous function
+    @Test
+    public void recurWithLambda() {
+        SExpression lambdaTailCall = evaluateString("((lambda (n) (if (= n  0) 'PASS (recur (- n 1)))) 2020)");
+        assertSExpressionsMatch(parseString("PASS"), lambdaTailCall);
+    }
 
-    // recur with nested anonymous function
+    @Test
-
+    public void recurWithNestedLambda() {
-    // test scope after failure in function, is it global again?
+        evaluateString("(defun nested-tail () ((lambda (n) (if (= n  0) 'PASS (recur (- n 1)))) 2020))");
+        assertSExpressionsMatch(parseString("PASS"), evaluateString("(nested-tail)"));
+    }
 
 }

test/table/ExecutionContextTest.java

@@ -1,8 +1,10 @@
 package table;
 
+import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
 import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertThat;
 import static sexpression.Nil.NIL;
 import static sexpression.Symbol.T;
 
@@ -85,4 +87,18 @@ public class ExecutionContextTest {
         assertEquals(NIL, executionContext.lookupSymbolValue("shadowed"));
     }
 
+    @Test
+    public void restoreGlobalContext() {
+        SymbolTable global = executionContext.getScope();
+        SymbolTable scope1 = new SymbolTable(global);
+        SymbolTable scope2 = new SymbolTable(scope1);
+        SymbolTable scope3 = new SymbolTable(scope2);
+        executionContext.setScope(scope3);
+
+        assertThat(executionContext.getScope().isGlobal(), is(false));
+        executionContext.restoreGlobalScope();
+        assertThat(executionContext.getScope().isGlobal(), is(true));
+        assertThat(executionContext.getScope(), is(global));
+    }
+
 }