Урок 5. Логические выражения, оператор if/else

program.txt

@@ -3,4 +3,9 @@ word2 = PI + word
 str = "a" * 5 + "ba" * 7 + "\n"
 print str * "3" * 2
 print "word = " + word + "\n"
-print "word2 = " + word2
+print "word2 = " + word2 + "\n"
+print "1" > "abc"
+print "\n"
+if (1 < 2) print "1 = 1"
+else print "1 != 1"
+print "\n"

src/com/annimon/ownlang/lib/NumberValue.java

@@ -8,6 +8,10 @@ public final class NumberValue implements Value {
     
     private final double value;
     
+    public NumberValue(boolean value) {
+        this.value = value ? 1 : 0;
+    }
+
     public NumberValue(double value) {
         this.value = value;
     }

src/com/annimon/ownlang/parser/Lexer.java

@@ -9,12 +9,12 @@ import java.util.List;
  */
 public final class Lexer {
     
-    private static final String OPERATOR_CHARS = "+-*/()=";
+    private static final String OPERATOR_CHARS = "+-*/()=<>";
     private static final TokenType[] OPERATOR_TOKENS = {
         TokenType.PLUS, TokenType.MINUS,
         TokenType.STAR, TokenType.SLASH,
         TokenType.LPAREN, TokenType.RPAREN,
-        TokenType.EQ
+        TokenType.EQ, TokenType.LT, TokenType.GT
     };
 
     private final String input;
@@ -98,10 +98,13 @@ public final class Lexer {
         }
         
         final String word = buffer.toString();
-        if (word.equals("print")) {
-            addToken(TokenType.PRINT);
-        } else {
-            addToken(TokenType.WORD, word);
+        switch (word) {
+            case "print": addToken(TokenType.PRINT); break;
+            case "if": addToken(TokenType.IF); break;
+            case "else": addToken(TokenType.ELSE); break;
+            default:
+                addToken(TokenType.WORD, word);
+                break;
         }
     }
     

src/com/annimon/ownlang/parser/Parser.java

@@ -3,8 +3,10 @@ package com.annimon.ownlang.parser;
 import com.annimon.ownlang.parser.ast.PrintStatement;
 import com.annimon.ownlang.parser.ast.AssignmentStatement;
 import com.annimon.ownlang.parser.ast.BinaryExpression;
+import com.annimon.ownlang.parser.ast.ConditionalExpression;
 import com.annimon.ownlang.parser.ast.VariabletExpression;
 import com.annimon.ownlang.parser.ast.Expression;
+import com.annimon.ownlang.parser.ast.IfStatement;
 import com.annimon.ownlang.parser.ast.ValueExpression;
 import com.annimon.ownlang.parser.ast.Statement;
 import com.annimon.ownlang.parser.ast.UnaryExpression;
@@ -41,6 +43,9 @@ public final class Parser {
         if (match(TokenType.PRINT)) {
             return new PrintStatement(expression());
         }
+        if (match(TokenType.IF)) {
+            return ifElse();
+        }
         return assignmentStatement();
     }
     
@@ -55,10 +60,43 @@ public final class Parser {
         throw new RuntimeException("Unknown statement");
     }
     
+    private Statement ifElse() {
+        final Expression condition = expression();
+        final Statement ifStatement = statement();
+        final Statement elseStatement;
+        if (match(TokenType.ELSE)) {
+            elseStatement = statement();
+        } else {
+            elseStatement = null;
+        }
+         return new IfStatement(condition, ifStatement, elseStatement);
+    }
     
     
     private Expression expression() {
-        return additive();
+        return conditional();
+    }
+    
+    private Expression conditional() {
+        Expression result = additive();
+        
+        while (true) {
+            if (match(TokenType.EQ)) {
+                result = new ConditionalExpression('=', result, additive());
+                continue;
+            }
+            if (match(TokenType.LT)) {
+                result = new ConditionalExpression('<', result, additive());
+                continue;
+            }
+            if (match(TokenType.GT)) {
+                result = new ConditionalExpression('>', result, additive());
+                continue;
+            }
+            break;
+        }
+        
+        return result;
     }
     
     private Expression additive() {

src/com/annimon/ownlang/parser/TokenType.java

@@ -13,12 +13,16 @@ public enum TokenType {
     
     // keyword
     PRINT,
+    IF,
+    ELSE,
     
     PLUS,
     MINUS,
     STAR,
     SLASH,
     EQ,
+    LT,
+    GT,
     
     LPAREN, // (
     RPAREN, // )

src/com/annimon/ownlang/parser/ast/ConditionalExpression.java

@@ -0,0 +1,53 @@
+package com.annimon.ownlang.parser.ast;
+
+import com.annimon.ownlang.lib.NumberValue;
+import com.annimon.ownlang.lib.StringValue;
+import com.annimon.ownlang.lib.Value;
+
+/**
+ *
+ * @author aNNiMON
+ */
+public final class ConditionalExpression implements Expression {
+    
+    private final Expression expr1, expr2;
+    private final char operation;
+
+    public ConditionalExpression(char operation, Expression expr1, Expression expr2) {
+        this.operation = operation;
+        this.expr1 = expr1;
+        this.expr2 = expr2;
+    }
+
+    @Override
+    public Value eval() {
+        final Value value1 = expr1.eval();
+        final Value value2 = expr2.eval();
+        if (value1 instanceof StringValue) {
+            final String string1 = value1.asString();
+            final String string2 = value2.asString();
+            switch (operation) {
+                case '<': return new NumberValue(string1.compareTo(string2) < 0);
+                case '>': return new NumberValue(string1.compareTo(string2) > 0);
+                case '=': 
+                default:
+                    return new NumberValue(string1.equals(string2));
+            }
+        }
+        
+        final double number1 = value1.asNumber();
+        final double number2 = value2.asNumber();
+        switch (operation) {
+            case '<': return new NumberValue(number1 < number2);
+            case '>': return new NumberValue(number1 > number2);
+            case '=': 
+            default:
+                return new NumberValue(number1 == number2);
+        }
+    }
+
+    @Override
+    public String toString() {
+        return String.format("[%s %c %s]", expr1, operation, expr2);
+    }
+}

src/com/annimon/ownlang/parser/ast/IfStatement.java

@@ -0,0 +1,37 @@
+package com.annimon.ownlang.parser.ast;
+
+/**
+ *
+ * @author aNNiMON
+ */
+public final class IfStatement implements Statement {
+    
+    private final Expression expression;
+    private final Statement ifStatement, elseStatement;
+
+    public IfStatement(Expression expression, Statement ifStatement, Statement elseStatement) {
+        this.expression = expression;
+        this.ifStatement = ifStatement;
+        this.elseStatement = elseStatement;
+    }
+    
+    @Override
+    public void execute() {
+        final double result = expression.eval().asNumber();
+        if (result != 0) {
+            ifStatement.execute();
+        } else if (elseStatement != null) {
+            elseStatement.execute();
+        }
+    }
+
+    @Override
+    public String toString() {
+        final StringBuilder result = new StringBuilder();
+        result.append("if ").append(expression).append(' ').append(ifStatement);
+        if (elseStatement != null) {
+            result.append("\nelse ").append(elseStatement);
+        }
+        return result.toString();
+    }
+}