Added unit tests and refactored the let form

Wrote a lisp program to calculate the number of bi-weekly paydays in a year

lisp/paydays.lisp

@@ -0,0 +1,11 @@
+(let ((*first-payday-day* 6)
+      (*leap-year* 0)
+      (*days-in-year* 365)
+      (*two-weeks* 14))
+
+  (+ 1
+     (/ (- (+ *days-in-year*
+              *leap-year*)
+           *first-payday-day*)
+        *two-weeks*))
+)

src/function/builtin/special/LET.java

@@ -6,94 +6,82 @@ import sexpression.*;
 import table.*;
 
 public class LET extends LispFunction {
-    
+
+    private ArgumentValidator argumentValidator;
     private ExecutionContext executionContext;
-    
+    private SymbolTable localScope;
+
     public LET() {
+        this.argumentValidator = new ArgumentValidator("LET");
+        this.argumentValidator.setMinimumNumberOfArguments(1);
+        this.argumentValidator.setFirstArgumentExpectedType(Cons.class);
         this.executionContext = ExecutionContext.getInstance();
     }
 
-    public SExpression call(Cons argList) {
+    public SExpression call(Cons argumentList) {
-        // make sure we have received at least one argument
+        argumentValidator.validate(argumentList);
-        if (argList.nullp()) {
+        Cons variableDefinitions = (Cons) argumentList.getCar();
-            throw new RuntimeException("too few arguments given to LET");
+        Cons body = (Cons) argumentList.getCdr();
-        }
 
-        // create a new symbol table on top of the current environment to add
+        return evaluateInScope(variableDefinitions, body);
-        // all the local variables to
-        SymbolTable environment = new SymbolTable(executionContext.getScope());
-
-        SExpression car = argList.getCar();
-        Cons cdr = (Cons) argList.getCdr();
-
-        addVariablesToTable(environment, car);
-        executionContext.setScope(environment);
-
-        SExpression retval = Nil.getInstance();
-
-        // evaluate all S-expression in the body
-        while (cdr.consp()) {
-            retval = EVAL.eval(cdr.getCar());
-            cdr = (Cons) cdr.getCdr();
-        }
-
-        // restore the environment to its original value
-        executionContext.setScope(environment.getParent());
-
-        return retval;
     }
 
-    // Add a list of variables and their values to the specified symbol table.
+    private SExpression evaluateInScope(Cons variableDefinitions, Cons body) {
-    //
+        createLocalScope(variableDefinitions);
-    // Parameters: environment - the symbol table to add the variables and
+        SExpression lastEvaluation = evaluateBody(body);
-    // their values to (must not be null)
+        restorePreviousScope();
-    // vars - a list of variable/value pairs (must be either a
+
-    // proper list of pairs or NIL)
+        return lastEvaluation;
-    // Throws: RuntimeException - Indicates that 'vars' is not a proper list or
+    }
-    // that it contains an member that is not a
+
-    // variable/value pair.
+    private SymbolTable createLocalScope(Cons variableDefinitions) {
-    // Precondition: 'environment' and 'vars' must not be null.
+        localScope = new SymbolTable(executionContext.getScope());
-    // Postcondition: All of the variables in 'vars' have been placed into
+        addVariablesToScope(localScope, variableDefinitions);
-    // 'environment' with their values.
+        executionContext.setScope(localScope);
-    private void addVariablesToTable(SymbolTable environment, SExpression vars) {
+
-        // makes sure the list of variable/value pairs is a list
+        return localScope;
-        if (!vars.listp()) {
+    }
-            throw new RuntimeException("LET: " + vars + " is not a properly formatted" + " variable/value pair list");
+
+    private void addVariablesToScope(SymbolTable scope, Cons variableDefinitions) {
+        validateAllPairsAreLists(variableDefinitions);
+
+        for (; variableDefinitions.consp(); variableDefinitions = (Cons) variableDefinitions.getCdr()) {
+            Cons symbolValuePair = (Cons) variableDefinitions.getCar();
+
+            validatePair(symbolValuePair);
+
+            Cons restOfPair = (Cons) symbolValuePair.getCdr();
+            SExpression symbol = symbolValuePair.getCar();
+            SExpression value = restOfPair.getCar();
+
+            scope.put(symbol.toString(), EVAL.eval(value));
         }
+    }
 
-        // add all variables in 'vars' to 'environment'
+    private void validateAllPairsAreLists(Cons variableDefinitions) {
-        while (vars.consp()) {
+        ArgumentValidator variableDefinitionListValidator = new ArgumentValidator("LET|argumentList|");
-            Cons varList = (Cons) vars;
+        variableDefinitionListValidator.setEveryArgumentExpectedType(Cons.class);
-            SExpression varListCar = varList.getCar();
+        variableDefinitionListValidator.validate(variableDefinitions);
+    }
 
-            // make sure this variable/value pair is a list
+    private void validatePair(Cons symbolValuePair) {
-            if (!varListCar.consp()) {
+        ArgumentValidator pairValidator = new ArgumentValidator("LET|pair|");
-                throw new RuntimeException("LET: " + varListCar + " is not a properly formatted"
+        pairValidator.setExactNumberOfArguments(2);
-                                           + " variable/value pair");
+        pairValidator.setFirstArgumentExpectedType(Symbol.class);
-            }
+        pairValidator.validate((Cons) symbolValuePair);
+    }
 
-            Cons varSpec = (Cons) varListCar;
+    private SExpression evaluateBody(Cons body) {
-            SExpression symbol = varSpec.getCar();
+        SExpression lastEvaluation = Nil.getInstance();
-            SExpression varSpecCdr = varSpec.getCdr();
 
-            // make sure this variable pair has a value associated with it
+        for (; body.consp(); body = (Cons) body.getCdr())
-            if (!varSpecCdr.consp()) {
+            lastEvaluation = EVAL.eval(body.getCar());
-                throw new RuntimeException("LET: illegal variable " + "specification " + varSpec);
-            }
 
-            Cons varValue = (Cons) varSpecCdr;
+        return lastEvaluation;
-            SExpression value = varValue.getCar();
+    }
 
-            // make sure there are no more members of this variable/value pair
+    private void restorePreviousScope() {
-            // and that 'symbol' is actually a symbol
+        executionContext.setScope(localScope.getParent());
-            if ((!varValue.getCdr().nullp()) || (!symbol.symbolp())) {
-                throw new RuntimeException("LET: illegal variable " + "specification " + varSpec);
-            }
-
-            environment.put(symbol.toString(), value);
-
-            vars = varList.getCdr();
-        }
     }
 
     public boolean evaluateArguments() {

test/function/builtin/special/LETTester.java

@@ -0,0 +1,141 @@
+package function.builtin.special;
+
+import static testutil.TestUtilities.*;
+
+import org.junit.*;
+
+import function.ArgumentValidator.*;
+import function.builtin.EVAL.UndefinedSymbolException;
+import sexpression.*;
+import table.ExecutionContext;
+
+public class LETTester {
+
+    private ExecutionContext executionContext;
+
+    public LETTester() {
+        this.executionContext = ExecutionContext.getInstance();
+    }
+
+    @Before
+    public void setUp() {
+        executionContext.clearContext();
+    }
+
+    @Test
+    public void simpleLet() {
+        String input = "(let ((x 1)) x)";
+
+        assertSExpressionsMatch(new LispNumber("1"), evaluateString(input));
+    }
+
+    @Test
+    public void emptyLet_ReturnsNil() {
+        String input = "(let ())";
+
+        assertSExpressionsMatch(Nil.getInstance(), evaluateString(input));
+    }
+
+    @Test
+    public void letWithSetf_DoesNotAlterGlobalVariable() {
+        String before = "(setf x 22)";
+        String input = "(let ((x 1)) x)";
+        String after = "x";
+
+        assertSExpressionsMatch(new LispNumber("22"), evaluateString(before));
+        assertSExpressionsMatch(new LispNumber("1"), evaluateString(input));
+        assertSExpressionsMatch(new LispNumber("22"), evaluateString(after));
+    }
+
+    @Test
+    public void letWithNestedSetf_DoesNotAlterGlobalVariable() {
+        String before = "(setf x 22)";
+        String input = "(let ((x 33)) (setf x 44) x)";
+        String after = "x";
+
+        assertSExpressionsMatch(new LispNumber("22"), evaluateString(before));
+        assertSExpressionsMatch(new LispNumber("44"), evaluateString(input));
+        assertSExpressionsMatch(new LispNumber("22"), evaluateString(after));
+    }
+
+    @Test
+    public void nestedLet() {
+        String input = "(let ((x 1)) (let ((y (+ 1 x))) y))";
+
+        assertSExpressionsMatch(new LispNumber("2"), evaluateString(input));
+    }
+
+    @Test
+    public void alterGlobalVariableFromLet() {
+        String before = "(setf x 1)";
+        String input = "(let ((y 1)) (setf x 2))";
+        String after = "x";
+
+        assertSExpressionsMatch(new LispNumber("1"), evaluateString(before));
+        assertSExpressionsMatch(new LispNumber("2"), evaluateString(input));
+        assertSExpressionsMatch(new LispNumber("2"), evaluateString(after));
+    }
+
+    @Test
+    public void accessGlobalVariableFromLet() {
+        String before = "(setf x 1)";
+        String input = "(let () x)";
+
+        assertSExpressionsMatch(new LispNumber("1"), evaluateString(before));
+        assertSExpressionsMatch(new LispNumber("1"), evaluateString(input));
+    }
+
+    @Test(expected = UndefinedSymbolException.class)
+    public void letDoesNotSetGlobalVariable() {
+        String input = "(let ((x 1)) nil)";
+
+        evaluateString(input);
+        evaluateString("x");
+    }
+
+    @Test(expected = BadArgumentTypeException.class)
+    public void testLetWithNonList() {
+        evaluateString("(let a)");
+    }
+
+    @Test(expected = BadArgumentTypeException.class)
+    public void testLetWithNoPairs() {
+        evaluateString("(let (a))");
+    }
+
+    @Test(expected = TooFewArgumentsException.class)
+    public void testLetWithTooFewItemsInPair() {
+        evaluateString("(let ((a)))");
+    }
+
+    @Test(expected = TooManyArgumentsException.class)
+    public void testLetWithTooManyItemsInPair() {
+        evaluateString("(let ((a b c)))");
+    }
+
+    @Test(expected = BadArgumentTypeException.class)
+    public void testLetWithNonSymbolInPair() {
+        evaluateString("(let ((1 b)))");
+    }
+
+    @Test(expected = TooFewArgumentsException.class)
+    public void testLetWithTooFewArguments() {
+        evaluateString("(let)");
+    }
+
+    @Test(expected = DottedArgumentListException.class)
+    public void testLetWithDottedArgumentList() {
+        evaluateString("(apply 'let (cons 'a 'b))");
+    }
+
+    @Test(expected = DottedArgumentListException.class)
+    public void testLetWithDottedPairList() {
+        evaluateString("(apply 'let (cons (cons 'a 'b) nil))");
+    }
+
+    @Test(expected = DottedArgumentListException.class)
+    public void testLetWithDottedPair() {
+        evaluateString("(apply 'let (cons (cons (cons 'a 'b) nil) nil))");
+    }
+
+}