Improved Evaluation

MathPad/MPTokenStream.m

@@ -0,0 +1,90 @@
+//
+//  MPTokenStream.m
+//  MathPad
+//
+//  Created by Kim Wittenburg on 20.09.14.
+//  Copyright (c) 2014 Kim Wittenburg. All rights reserved.
+//
+
+#import "MPTokenStream.h"
+
+@interface MPTokenStream ()
+@property (readwrite, nonatomic) NSUInteger currentLocation;
+@end
+
+@implementation MPTokenStream {
+    NSUInteger currentTokenIndex;
+    NSUInteger eofLocation;
+}
+
+- (instancetype)initWithTokens:(NSArray *)tokens
+{
+    self = [super init];
+    if (self) {
+        self.tokens = tokens;
+        self.ignoringWhitespaceTokens  = YES;
+        if (tokens.count > 0) {
+            eofLocation = NSMaxRange([tokens.lastObject range]);
+        }
+        [self reset];
+    }
+    return self;
+}
+
+- (void)skipWhitespaces
+{
+    if (!self.isIgnoringWhitespaceTokens) {
+        return;
+    }
+    while (currentTokenIndex < self.tokens.count) {
+        MPToken *token = self.tokens[currentTokenIndex];
+        if (token.tokenType != MPWhitespaceToken) {
+            return;
+        }
+        self.currentLocation = NSMaxRange(token.range);
+        ++currentTokenIndex;
+    }
+}
+
+- (void)reset
+{
+    currentTokenIndex = 0;
+    self.currentLocation = 0;
+    [self skipWhitespaces];
+}
+
+- (BOOL)hasMoreTokens
+{
+    [self skipWhitespaces];
+    return currentTokenIndex < self.tokens.count;
+}
+
+- (MPToken *)nextToken
+{
+    [self skipWhitespaces];
+    if (currentTokenIndex >= self.tokens.count) {
+        return [[MPToken alloc] initEOFTokenAtLocation:eofLocation];
+    } else {
+        MPToken *token = self.tokens[currentTokenIndex++];
+        self.currentLocation = NSMaxRange(token.range);
+        return token;
+    }
+}
+
+- (MPToken *)nextTokenOfType:(MPTokenType)type
+{
+    [self skipWhitespaces];
+    if (currentTokenIndex >= self.tokens.count) {
+        return nil;
+    } else {
+        MPToken *token = self.tokens[currentTokenIndex];
+        if (token.tokenType != type) {
+            return nil;
+        }
+        ++currentTokenIndex;
+        self.currentLocation = NSMaxRange(token.range);
+        return token;
+    }
+}
+
+@end