1 files changed, 207 insertions, 0 deletions
diff --git a/src/com/craftinginterpreters/lox/Scanner.java b/src/com/craftinginterpreters/lox/Scanner.java
new file mode 100644
index 0000000..e21f701
--- /dev/null
+++ b/src/com/craftinginterpreters/lox/Scanner.java
@@ -0,0 +1,207 @@
+package com.craftinginterpreters.lox;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static com.craftinginterpreters.lox.TokenType.*;
+
+class Scanner {
+    private final String source;
+    private final List<Token> tokens = new ArrayList<>();
+    private int start = 0;
+    private int current = 0;
+    private int line = 1;
+    private static final Map<String, TokenType> keywords;
+
+    static {
+        keywords = new HashMap<>();
+        keywords.put("and", AND);
+        keywords.put("class", CLASS);
+        keywords.put("else", ELSE);
+        keywords.put("false", FALSE);
+        keywords.put("for", FOR);
+        keywords.put("fun", FUN);
+        keywords.put("if", IF);
+        keywords.put("nil", NIL);
+        keywords.put("or", OR);
+        keywords.put("print", PRINT);
+        keywords.put("return", RETURN);
+        keywords.put("super", SUPER);
+        keywords.put("this", THIS);
+        keywords.put("true", TRUE);
+        keywords.put("var", VAR);
+        keywords.put("while", WHILE);
+    }
+
+    Scanner(String source) {
+        this.source = source;
+    }
+
+    List<Token> scanTokens() {
+        while (!isAtEnd()) {
+            // We are at the beginning of the next lexeme.
+            start = current;
+            scanToken();
+        }
+
+        tokens.add(new Token(EOF, "", null, line));
+        return tokens;
+    }
+
+    private void scanToken() {
+        char c = advance();
+
+        switch (c) {
+        case '(': addToken(LEFT_PAREN); break;
+        case ')': addToken(RIGHT_PAREN); break;
+        case '{': addToken(LEFT_BRACE); break;
+        case '}': addToken(RIGHT_BRACE); break;
+        case ',': addToken(COMMA); break;
+        case '.': addToken(DOT); break;
+        case '-': addToken(MINUS); break;
+        case '+': addToken(PLUS); break;
+        case ';': addToken(SEMICOLON); break;
+        case '*': addToken(STAR); break;
+        case '!':
+            addToken(match('=') ? BANG_EQUAL : BANG);
+            break;
+        case '=':
+            addToken(match('=') ? EQUAL_EQUAL : EQUAL);
+            break;
+        case '<':
+            addToken(match('=') ? LESS_EQUAL : LESS);
+            break;
+        case '>':
+            addToken(match('=') ? GREATER_EQUAL : GREATER);
+            break;
+        case '/':
+            if (match('/')) {
+                // A comment goes until the end of the line.
+                while (peek() != '\n' && !isAtEnd()) advance();
+            } else {
+                addToken(SLASH);
+            }
+            break;
+            
+        case ' ':
+        case '\r':
+        case '\t':
+            // Ignore whitespace.
+            break;
+
+            // I guess this code isn't meant to run on Mac OS 9 and before.
+        case '\n':
+            line++;
+            break;
+
+        case '"': string(); break;
+
+        default:
+            if (isDigit(c)) {
+                number();
+            } else if (isAlpha(c)) {
+                identifier();
+            } else {
+                Lox.error(line, "Unexpected character.");
+            }
+            break;
+        }
+    }
+
+    private void identifier() {
+        while (isAlphaNumeric(peek())) advance();
+
+        String text = source.substring(start, current);
+        TokenType type = keywords.get(text);
+        if (type == null) type = IDENTIFIER;
+        addToken(type);
+    }
+
+    private void number() {
+        while (isDigit(peek())) advance();
+
+        // Look for a fractional part.
+        if (peek() == '.' && isDigit(peekNext())) {
+            // Consume the "."
+            advance();
+
+            while (isDigit(peek())) advance();
+        }
+
+        addToken(NUMBER,
+                 Double.parseDouble(source.substring(start, current)));
+    }
+
+    // I guess we won't be able to include escaped characters in the string? At
+    // least not escaped " characters.
+    private void string() {
+        while (peek() != '"' && !isAtEnd()) {
+            if (peek() == '\n') line++;
+            advance();
+        }
+
+        if (isAtEnd()) {
+            Lox.error(line, "Unterminated string.");
+            return;
+        }
+
+        // The closing ".
+        advance();
+
+        // Trim the surrounding quotes.
+        String value = source.substring(start + 1, current - 1);
+        addToken(STRING, value);
+    }
+
+    private boolean match(char expected) {
+        if (isAtEnd()) return false;
+        if (source.charAt(current) != expected) return false;
+
+        current++;
+        return true;
+    }
+
+    private char peek() {
+        if (isAtEnd()) return '\0';
+        return source.charAt(current);
+    }
+
+    private char peekNext() {
+        if (current + 1 >= source.length()) return '\0';
+        return source.charAt(current + 1);
+    }
+
+    private boolean isAlpha(char c) {
+        return (c >= 'a' && c <= 'z') ||
+            (c >= 'A' && c <= 'Z') ||
+            c == '_';
+    }
+
+    private boolean isAlphaNumeric(char c) {
+        return isAlpha(c) || isDigit(c);
+    }
+
+    private boolean isDigit(char c) {
+        return c >= '0' && c <= '9';
+    }
+
+    private boolean isAtEnd() {
+        return current >= source.length();
+    }
+
+    private char advance() {
+        current++;
+        return source.charAt(current - 1);
+    }
+
+    private void addToken(TokenType type) {
+        addToken(type, null);
+    }
+
+    private void addToken(TokenType type, Object literal) {
+        String text = source.substring(start, current);
+        tokens.add(new Token(type, text, literal, line));
+    }
+}