Basic Repl setup

app/src/main/java/org/barink/Lox.java

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+/*
+ * This Java source file was generated by the Gradle 'init' task.
+ */
+package org.barink;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+
+public class Lox {
+   static boolean hadError = false;
+   
+    public static void main(String[] args) {
+        if (args.length > 1){
+            System.out.println("Usage: jlox [script]");
+            System.exit(64);
+        } else if (args.length == 1) {
+            runFile(args[0]);
+        }else{
+            runPrompt();
+        }
+    }
+
+    private static void runFile(String path) throws IOException{
+        byte[] bytes = Files.readAllBytes(Paths.get(path));
+        run(new String(bytes, Charset.defaultCharset()));
+        if (hadError) System.exit(65);
+    }
+
+    private static void runPrompt() throws IOException{
+        InputStreamReader input = new InputStreamReader(System.in);
+        BufferedReader reader = new BufferedReader(input);
+
+        for(;;){
+            System.out.println("> ");
+            String line = reader.readLine();
+            if(line == null ) break;
+            run(line);
+            hadError = false;
+        }
+    }
+
+    private static void run(String source){
+        Scanner scanner = new Scanner(source);
+        List<Token> tokens = scanner.scanTokens();
+
+        // For now, just print the tokens
+        for (Token token : tokens){
+            System.out.println(token);
+        }
+    }
+
+    static void error(int line, String message){
+        report(line, "", message);
+    }
+
+    private static void report(int line, String where, String message){
+        hadError = true;
+    }
+
+
+}

app/src/main/java/org/barink/Scanner.java

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+package org.barink;
+
+import java.util.ArrayList;
+import java.util.List;
+
+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;
+
+    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(TokenType.EOF, "", null, line));
+        return tokens
+    }
+
+    private boolean isAtEnd(){
+        return current >= source.length();
+    }
+}

app/src/main/java/org/barink/Token.java

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+package org.barink;
+
+class Token {
+    final TokenType type;
+    final String lexeme;
+    final Object literal;
+    final int line;
+
+    Token(TokenType type, String lexeme, Object literal, int line){
+        this.type = type;
+        this.lexeme = lexeme;
+        this.literal = literal;
+        this.line = line;
+    }
+
+    public String toString(){
+        return type + " " + lexeme + " " + literal;
+    }
+}

app/src/main/java/org/barink/TokenType.java

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+package org.barink;
+
+enum TokenType {
+  // Single-character tokens.
+  LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE,
+  COMMA, DOT, MINUS, PLUS, SEMICOLON, SLASH, STAR,
+
+  // One or two character tokens. 
+  BANG, BANG_EQUAL,
+  EQUAL, EQUAL_EQUAL,
+  GREATER, GREATER_EQUAL,
+  LESS, LESS_EQUAL,
+  
+  // Literals
+  IDENTIFIER, STRING, NUMBER,
+
+  // Keywords
+  AND, CLASS, ELSE, FALSE, FUN, FOR, IF, NIL, OR,
+  PRINT, RETURN, SUPER, THIS, TRUE, VAR, WHILE,
+
+  EOF
+}
+
+