compiler.c

//
// Created by kroot on 19/7/19.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "common.h"
#include "compiler.h"
#include "memory.h"
#include "scanner.h"

#ifdef DEBUG_PRINT_CODE

#include "debug.h"

#endif

typedef struct {
    Token current;
    Token previous;
    bool hadError;
    bool panicMode;
} Parser;

typedef enum {
    PREC_NONE,
    PREC_ASSIGNMENT,
    PREC_OR,
    PREC_AND,
    PREC_EQUALITY,
    PREC_COMPARISON,
    PREC_TERM,
    PREC_FACTOR,
    PREC_UNARY,
    PREC_CALL,
    PREC_PRIMARY
} Precedence;

typedef void (* ParseFn)(bool canAssign);

typedef struct {
    ParseFn prefix;
    ParseFn infix;
    Precedence precedence;
} ParseRule;

typedef struct {
    Token name;
    int depth;
    bool isCaptured;
} Local;

typedef struct {
    uint8_t index;
    bool isLocal;
} Upvalue;

typedef enum {
    TYPE_FUNCTION,
    TYPE_INITIALIZER,
    TYPE_METHOD,
    TYPE_SCRIPT
} FunctionType;

typedef struct Compiler {
    struct Compiler* enclosing;
    ObjFunction* function;
    FunctionType type;
    Local locals[UINT8_COUNT];
    Upvalue upvalues[UINT8_COUNT];
    int localCount;
    int scopeDepth;
} Compiler;

typedef struct ClassCompiler {
    struct ClassCompiler* enclosing;
    Token name;
    bool hasSuperclass;
} ClassCompiler;

Parser parser;
ClassCompiler* currentClass = NULL;
Compiler* current = NULL;

static Chunk* currentChunk() {
    return &current->function->chunk;
}

static void errorAt(Token* token, const char* message) {
    if (parser.panicMode)
        return;
    parser.panicMode = true;
    fprintf(stderr, "[line %d] Error", token->line);

    if (token->type == TOKEN_EOF) {
        fprintf(stderr, " at end");
    } else if (token->type == TOKEN_ERROR) {

    } else {
        fprintf(stderr, " at '%.*s'", token->length, token->start);
    }

    fprintf(stderr, ": %s\n", message);
    parser.hadError = true;
}

static void error(const char* message) {
    errorAt(&parser.previous, message);
}

static void errorAtCurrent(const char* message) {
    errorAt(&parser.current, message);
}

static void advance() {
    parser.previous = parser.current;
    while (1) {
        parser.current = scanToken();
        if (parser.current.type != TOKEN_ERROR) break;

        errorAtCurrent(parser.current.start);
    }
}

static void consume(TokenType type, const char* message) {
    if (parser.current.type == type) {
        advance();
        return;
    }
    errorAtCurrent(message);
}

static bool check(TokenType type) {
    return parser.current.type == type;
}

static bool match(TokenType type) {
    if (!check(type)) return false;
    advance();
    return true;
}

static void emitByte(uint8_t byte) {
    writeChunk(currentChunk(), byte, parser.previous.line);
}

static void emitBytes(uint8_t byte1, uint8_t byte2) {
    emitByte(byte1);
    emitByte(byte2);
}

static void emitLoop(int loopStart) {
    emitByte(OP_LOOP);
    int offset = currentChunk()->count - loopStart + 2;
    if (offset > UINT16_MAX) error("Loop body too large.");
    emitByte((offset >> 8) & 0xff);
    emitByte(offset & 0xff);
}

static int emitJump(uint8_t instruction) {
    emitByte(instruction);
    emitByte(0xff);
    emitByte(0xff);
    return currentChunk()->count - 2;
}

static void emitReturn() {
    if (current->type == TYPE_INITIALIZER) {
        emitBytes(OP_GET_LOCAL, 0);
    } else {
        emitByte(OP_NIL);
    }
    emitByte(OP_RETURN);
}

static uint8_t makeConstant(Value value) {
    int constIndex = addConstant(currentChunk(), value);
    if (constIndex > UINT8_MAX) {
        error("Too many constants in chunk.");
        return 0;
    }

    return (uint8_t)constIndex;
}

static void emitConstant(Value value) {
    emitBytes(OP_CONSTANT, makeConstant(value));
}

static void patchJump(int offset) {
    int jump = currentChunk()->count - offset - 2;
    if (jump > UINT16_MAX) {
        error("Too much code to jump over.");
    }
    currentChunk()->code[offset] = (jump >> 8) & 0xff;
    currentChunk()->code[offset + 1] = jump & 0xff;
}

static void initCompiler(Compiler* compiler, FunctionType type) {
    compiler->enclosing = current;
    compiler->function = NULL;
    compiler->type = type;
    compiler->localCount = 0;
    compiler->scopeDepth = 0;
    compiler->function = newFunction();
    current = compiler;
    if (type != TYPE_SCRIPT) {
        current->function->name = copyString(parser.previous.start, parser.previous.length);
    }
    Local* local = &current->locals[current->localCount++];
    local->depth = 0;
    local->isCaptured = false;
    if (type != TYPE_FUNCTION) {
        local->name.start = "this";
        local->name.length = 4;
    } else {
        local->name.start = "";
        local->name.length = 0;
    }
}

static ObjFunction* endCompiler() {

    emitReturn();
    ObjFunction* function = current->function;
#ifdef DEBUG_PRINT_CODE
    if (!parser.hadError) {
        disassembleChunk(currentChunk(), function->name != NULL ? function->name->chars : "<wscript>");
    }
#endif
    current = current->enclosing;
    return function;
}

static void beginScope() {
    current->scopeDepth++;
}

static void endScope() {
    current->scopeDepth--;
    while (current->localCount > 0 && current->locals[current->localCount - 1].depth > current->scopeDepth) {
        if (current->locals[current->localCount - 1].isCaptured) {
            emitByte(OP_CLOSE_UPVALUE);
        } else {
            emitByte(OP_POP);
        }
        current->localCount--;
    }
}

static uint8_t argumentList();

static void and_(bool canAssign);

static void expression();

static void statement();

static void declaration();

static uint8_t identifierConstant(Token* name);

static ParseRule* getRule(TokenType type);

static void parsePrecedence(Precedence precedence);

static int resolveLocal(Compiler* compiler, Token* name);

static int resolveUpvalue(Compiler* compiler, Token* name);

static void binary(bool canAssign) {
    TokenType operatorType = parser.previous.type;

    ParseRule* rule = getRule(operatorType);
    parsePrecedence(rule->precedence + 1);

    switch (operatorType) {
        case TOKEN_BANG_EQUAL: emitBytes(OP_EQUAL, OP_NOT);
            break;
        case TOKEN_EQUAL_EQUAL: emitByte(OP_EQUAL);
            break;
        case TOKEN_GREATER: emitByte(OP_GREATER);
            break;
        case TOKEN_GREATER_EQUAL: emitBytes(OP_LESS, OP_NOT);
            break;
        case TOKEN_LESS: emitByte(OP_LESS);
            break;
        case TOKEN_LESS_EQUAL: emitBytes(OP_GREATER, OP_NOT);
            break;
        case TOKEN_PLUS: emitByte(OP_ADD);
            break;
        case TOKEN_MINUS: emitByte(OP_SUBTRACT);
            break;
        case TOKEN_STAR: emitByte(OP_MULTIPLY);
            break;
        case TOKEN_SLASH: emitByte(OP_DIVIDE);
            break;
        default: return;
    }
}

static void call(bool canAssign) {
    uint8_t argCount = argumentList();
    emitBytes(OP_CALL, argCount);
}

static void dot(bool canAssign) {
    consume(TOKEN_IDENTIFIER, "Expect identifier after '.'.");
    uint8_t name = identifierConstant(&parser.previous);
    if (canAssign && match(TOKEN_EQUAL)) {
        expression();
        emitBytes(OP_SET_PROPERTY, name);
    } else if (match(TOKEN_LEFT_PAREN)) {
        uint8_t argCount = argumentList();
        emitBytes(OP_INVOKE, name);
        emitByte(argCount);
    } else {
        emitBytes(OP_GET_PROPERTY, name);
    }
}

static void literal(bool canAssign) {
    switch (parser.previous.type) {
        case TOKEN_FALSE: emitByte(OP_FALSE);
            break;
        case TOKEN_TRUE: emitByte(OP_TRUE);
            break;
        case TOKEN_NIL: emitByte(OP_NIL);
            break;
        default: return;
    }
}

static void grouping(bool canAssign) {
    expression();
    consume(TOKEN_RIGHT_PAREN, "Expected ')' after expression.");
}

static void number(bool canAssign) {
    double value = strtod(parser.previous.start, NULL);
    emitConstant(NUMBER_VAL(value));
}

static void or_(bool canAssign) {
    int elseJump = emitJump(OP_JUMP_IF_FALSE);
    int endJump = emitJump(OP_JUMP);
    patchJump(elseJump);
    emitByte(OP_POP);
    parsePrecedence(PREC_OR);
    patchJump(endJump);
}

static void string(bool canAssign) {
    emitConstant(OBJ_VAL(copyString(parser.previous.start + 1, parser.previous.length - 2)));
}

static void namedVariable(Token name, bool canAssign) {
    uint8_t getOp, setOp;
    int arg = resolveLocal(current, &name);
    if (arg != -1) {
        getOp = OP_GET_LOCAL;
        setOp = OP_SET_LOCAL;
    } else if ((arg = resolveUpvalue(current, &name)) != -1) {
        getOp = OP_GET_UPVALUE;
        setOp = OP_SET_UPVALUE;
    } else {
        arg = identifierConstant(&name);
        getOp = OP_GET_GLOBAL;
        setOp = OP_SET_GLOBAL;
    }
    if (canAssign && match(TOKEN_EQUAL)) {
        expression();
        emitBytes(setOp, (uint8_t)arg);
    } else {
        emitBytes(getOp, (uint8_t)arg);
    }
}

static void variable(bool canAssign) {
    namedVariable(parser.previous, canAssign);
}

static Token syntheticToken(const char* text) {
    Token token;
    token.start = text;
    token.length = (int)strlen(text);
    return token;
}

static void super_(bool canAssign) {
    if (currentClass == NULL) {
        error("Cannot use 'super' outside of a class.");
    } else if (!currentClass->hasSuperclass) {
        error("Cannot use 'super' in a class with no superclass.");
    }
    consume(TOKEN_DOT, "Expect '.' after super keyword.");
    consume(TOKEN_IDENTIFIER, "Expect superclass method name.");
    uint8_t name = identifierConstant(&parser.previous);

    namedVariable(syntheticToken("this"), false);
    if (match(TOKEN_LEFT_PAREN)) {
        uint8_t argCount = argumentList();
        namedVariable(syntheticToken("super"), false);
        emitBytes(OP_SUPER_INVOKE, name);
        emitByte(argCount);
    } else {
        namedVariable(syntheticToken("super"), false);
        emitBytes(OP_GET_SUPER, name);
    }
}

static void this_(bool canAssign) {
    if (currentClass == NULL) {
        error("Cannot use 'this' outside class.");
        return;
    }
    variable(false);
}

static void unary(bool canAssign) {
    TokenType operatorType = parser.previous.type;
    parsePrecedence(PREC_UNARY);
    switch (operatorType) {
        case TOKEN_BANG: emitByte(OP_NOT);
            break;
        case TOKEN_MINUS: emitByte(OP_NEGATE);
            break;
        default: return;
    }
}

ParseRule rules[] = {
        {grouping, call,   PREC_CALL},       // TOKEN_LEFT_PAREN
        {NULL,     NULL,   PREC_NONE},       // TOKEN_RIGHT_PAREN
        {NULL,     NULL,   PREC_NONE},       // TOKEN_LEFT_BRACE
        {NULL,     NULL,   PREC_NONE},       // TOKEN_RIGHT_BRACE
        {NULL,     NULL,   PREC_NONE},       // TOKEN_COMMA
        {NULL,     dot,    PREC_CALL},       // TOKEN_DOT
        {unary,    binary, PREC_TERM},       // TOKEN_MINUS
        {NULL,     binary, PREC_TERM},       // TOKEN_PLUS
        {NULL,     NULL,   PREC_NONE},       // TOKEN_SEMICOLON
        {NULL,     binary, PREC_FACTOR},     // TOKEN_SLASH
        {NULL,     binary, PREC_FACTOR},     // TOKEN_STAR
        {unary,    NULL,   PREC_NONE},       // TOKEN_BANG
        {NULL,     binary, PREC_EQUALITY},   // TOKEN_BANG_EQUAL
        {NULL,     NULL,   PREC_NONE},       // TOKEN_EQUAL
        {NULL,     binary, PREC_EQUALITY},   // TOKEN_EQUAL_EQUAL
        {NULL,     binary, PREC_COMPARISON}, // TOKEN_GREATER
        {NULL,     binary, PREC_COMPARISON}, // TOKEN_GREATER_EQUAL
        {NULL,     binary, PREC_COMPARISON}, // TOKEN_LESS
        {NULL,     binary, PREC_COMPARISON}, // TOKEN_LESS_EQUAL
        {variable, NULL,   PREC_NONE},       // TOKEN_IDENTIFIER
        {string,   NULL,   PREC_NONE},       // TOKEN_STRING
        {number,   NULL,   PREC_NONE},       // TOKEN_NUMBER
        {NULL,     and_,   PREC_AND},        // TOKEN_AND
        {NULL,     NULL,   PREC_NONE},       // TOKEN_CLASS
        {NULL,     NULL,   PREC_NONE},       // TOKEN_DEF
        {NULL,     NULL,   PREC_NONE},       // TOKEN_ELSE
        {literal,  NULL,   PREC_NONE},       // TOKEN_FALSE
        {NULL,     NULL,   PREC_NONE},       // TOKEN_FOR
        {NULL,     NULL,   PREC_NONE},       // TOKEN_IF
        {literal,  NULL,   PREC_NONE},       // TOKEN_NIL
        {NULL,     or_,    PREC_OR},         // TOKEN_OR
        {NULL,     NULL,   PREC_NONE},       // TOKEN_PRINT
        {NULL,     NULL,   PREC_NONE},       // TOKEN_RETURN
        {super_,   NULL,   PREC_NONE},       // TOKEN_SUPER
        {this_,    NULL,   PREC_NONE},       // TOKEN_THIS
        {literal,  NULL,   PREC_NONE},       // TOKEN_TRUE
        {NULL,     NULL,   PREC_NONE},       // TOKEN_VAR
        {NULL,     NULL,   PREC_NONE},       // TOKEN_WHILE
        {NULL,     NULL,   PREC_NONE},       // TOKEN_ERROR
        {NULL,     NULL,   PREC_NONE},       // TOKEN_EOF
};

void parsePrecedence(Precedence precedence) {
    advance();
    ParseFn prefixRule = getRule(parser.previous.type)->prefix;
    if (prefixRule == NULL) {
        error("Expect expression.");
        return;
    }

    bool canAssign = precedence <= PREC_ASSIGNMENT;
    prefixRule(canAssign);

    while (precedence <= getRule(parser.current.type)->precedence) {
        advance();
        ParseFn infixRule = getRule(parser.previous.type)->infix;
        infixRule(canAssign);
    }

    if (canAssign && match(TOKEN_EQUAL)) {
        error("Invalid assignment target.");
        expression();
    }
}

static ParseRule* getRule(TokenType type) {
    return &rules[type];
}

static uint8_t identifierConstant(Token* name) {
    return makeConstant(OBJ_VAL(copyString(name->start, name->length)));
}

static void addLocal(Token name) {
    if (current->localCount == UINT8_COUNT) {
        error("Too many locals.");
        return;
    }
    Local* local = &current->locals[current->localCount++];
    local->name = name;
    local->depth = -1;
    local->isCaptured = false;
}

static bool identifiersEqual(Token* a, Token* b) {
    if (a->length != b->length) return false;
    return memcmp(a->start, b->start, a->length) == 0;
}

static int resolveLocal(Compiler* compiler, Token* name) {
    for (int i = compiler->localCount - 1; i >= 0; i--) {
        Local* local = &compiler->locals[i];
        if (identifiersEqual(name, &local->name)) {
            if (local->depth == -1) {
                error("Cannot read local variable in its own initializer.");
            }
            return i;
        }
    }
    return -1;
}

static int addUpvalue(Compiler* compiler, uint8_t index, bool isLocal) {
    int upvalueCount = compiler->function->upvalueCount;

    for (int i = 0; i < upvalueCount; ++i) {
        Upvalue* upvalue = &compiler->upvalues[i];
        if (upvalue->index == index && upvalue->isLocal == isLocal) {
            return i;
        }
    }

    if (upvalueCount == UINT8_COUNT) {
        error("Too many closure variables");
        return 0;
    }

    compiler->upvalues[upvalueCount].index = index;
    compiler->upvalues[upvalueCount].isLocal = isLocal;
    return compiler->function->upvalueCount++;
}

static int resolveUpvalue(Compiler* compiler, Token* name) {
    if (compiler->enclosing == NULL) return -1;

    int local = resolveLocal(compiler->enclosing, name);
    if (local != -1) {
        compiler->enclosing->locals[local].isCaptured = true;
        return addUpvalue(compiler, (uint8_t)local, true);
    }

    int upvalue = resolveUpvalue(compiler->enclosing, name);
    if (upvalue != -1) {
        return addUpvalue(compiler, (uint8_t)upvalue, false);
    }

    return -1;
}

static void declareVariable() {
    if (current->scopeDepth == 0) return;
    Token* name = &parser.previous;
    for (int i = current->localCount - 1; i >= 0; i--) {
        Local* local = &current->locals[i];
        if (local->depth != -1 && local->depth < current->scopeDepth) {
            break;
        }
        if (identifiersEqual(name, &local->name)) {
            error("Variable already declared.");
        }
    }
    addLocal(*name);
}

static uint8_t parseVariable(const char* errorMessage) {
    consume(TOKEN_IDENTIFIER, errorMessage);
    declareVariable();

    if (current->scopeDepth > 0)
        return 0;

    return identifierConstant(&parser.previous);
}

static void markInitialized() {
    if (current->scopeDepth == 0) return;
    current->locals[current->localCount - 1].depth = current->scopeDepth;
}

static void defineVariable(uint8_t global) {
    markInitialized();
    if (current->scopeDepth > 0) {
        return;
    }
    emitBytes(OP_DEFINE_GLOBAL, global);
}

static uint8_t argumentList() {
    uint8_t argCount = 0;
    if (!check(TOKEN_RIGHT_PAREN)) {
        do {
            expression();
            if (argCount == 255) {
                error("Cannot have more than 255 args.");
            }
            argCount++;
        } while (match(TOKEN_COMMA));
    }
    consume(TOKEN_RIGHT_PAREN, "Expect ')' after arguments.");
    return argCount;
}

static void and_(bool canAssign) {
    int endJump = emitJump(OP_JUMP_IF_FALSE);
    emitByte(OP_POP);
    parsePrecedence(PREC_AND);
    patchJump(endJump);
}

void expression() {
    parsePrecedence(PREC_ASSIGNMENT);
}

static void block() {
    while (!check(TOKEN_RIGHT_BRACE) && !check(TOKEN_EOF)) {
        declaration();
    }
    consume(TOKEN_RIGHT_BRACE, "Expect '}' after block.");
}

static void function(FunctionType type) {
    Compiler compiler;
    initCompiler(&compiler, type);
    beginScope();
    consume(TOKEN_LEFT_PAREN, "Expect '(' after function name.");
    if (!check(TOKEN_RIGHT_PAREN)) {
        do {
            current->function->arity++;
            if (current->function->arity > 255) {
                errorAtCurrent("Can't have more than 255 params.");
            }
            uint8_t paramConstant = parseVariable("Expect parameter name.");
            defineVariable(paramConstant);
        } while (match(TOKEN_COMMA));
    }
    consume(TOKEN_RIGHT_PAREN, "Expect ')' after parameters.");
    consume(TOKEN_LEFT_BRACE, "Expect '{' before function body.");
    block();
    ObjFunction* func = endCompiler();
    emitBytes(OP_CLOSURE, makeConstant(OBJ_VAL(func)));
    for (int i = 0; i < func->upvalueCount; ++i) {
        emitByte(compiler.upvalues[i].isLocal ? 1 : 0);
        emitByte(compiler.upvalues[i].index);
    }
}

static void method() {
    consume(TOKEN_IDENTIFIER, "Expect method name.");
    uint8_t constant = identifierConstant(&parser.previous);

    FunctionType type = TYPE_METHOD;
    if (parser.previous.length == 4 && memcmp(parser.previous.start, "init", 4) == 0) {
        type = TYPE_INITIALIZER;
    }
    function(type);

    emitBytes(OP_METHOD, constant);
}

static void classDeclaration() {
    consume(TOKEN_IDENTIFIER, "Expect class name.");
    Token className = parser.previous;
    uint8_t nameConstant = identifierConstant(&parser.previous);
    declareVariable();
    emitBytes(OP_CLASS, nameConstant);
    defineVariable(nameConstant);

    ClassCompiler classCompiler;
    classCompiler.name = className;
    classCompiler.hasSuperclass = false;
    classCompiler.enclosing = currentClass;
    currentClass = &classCompiler;

    if (match(TOKEN_LESS)) {
        consume(TOKEN_IDENTIFIER, "Expect superclass name.");
        variable(false);
        if (identifiersEqual(&className, &parser.previous)) {
            error("A class cannot inherit from itself.");
        }

        beginScope();
        addLocal(syntheticToken("super"));
        defineVariable(0);

        namedVariable(className, false);
        emitByte(OP_INHERIT);
        classCompiler.hasSuperclass = true;
    }

    namedVariable(className, false);
    consume(TOKEN_LEFT_BRACE, "Expect '{' before function body.");
    while (!check(TOKEN_RIGHT_BRACE) && !check(TOKEN_EOF)) {
        method();
    }
    consume(TOKEN_RIGHT_BRACE, "Expect '}' after function body.");
    emitByte(OP_POP);

    if (classCompiler.hasSuperclass) {
        endScope();
    }
    currentClass = currentClass->enclosing;
}

static void funcDeclaration() {
    uint8_t global = parseVariable("Expect function name.");
    markInitialized();
    function(TYPE_FUNCTION);
    defineVariable(global);
}

static void varDeclaration() {
    uint8_t global = parseVariable("Expect variable name");
    if (match(TOKEN_EQUAL)) {
        expression();
    } else {
        emitByte(OP_NIL);
    }
    consume(TOKEN_SEMICOLON, "Expect ';' after variable declaration.");
    defineVariable(global);
}

static void expressionStatement() {
    expression();
    consume(TOKEN_SEMICOLON, "Expect ';' after expression.");
    emitByte(OP_POP);
}

static void forStatement() {
    beginScope();
    consume(TOKEN_LEFT_PAREN, "Expect '(' after 'for'.");
    if (match(TOKEN_VAR)) {
        varDeclaration();
    } else if (match(TOKEN_SEMICOLON)) {
        // No initializer
    } else {
        expressionStatement();
    }
    int loopStart = currentChunk()->count;

    int exitJump = -1;
    if (!match(TOKEN_SEMICOLON)) {
        expression();
        consume(TOKEN_SEMICOLON, "Expect ';' after loop condition.");
        exitJump = emitJump(OP_JUMP_IF_FALSE);
        emitByte(OP_POP);
    }
    if (!match(TOKEN_RIGHT_PAREN)) {
        int bodyJump = emitJump(OP_JUMP);
        int incrStart = currentChunk()->count;
        expression();
        emitByte(OP_POP);
        consume(TOKEN_RIGHT_PAREN, "Expect ')' after for clauses.");
        emitLoop(loopStart);
        loopStart = incrStart;
        patchJump(bodyJump);
    }
    statement();
    emitLoop(loopStart);
    if (exitJump != -1) {
        patchJump(exitJump);
        emitByte(OP_POP);
    }
    endScope();
}

static void ifStatement() {
    consume(TOKEN_LEFT_PAREN, "Expect '(' after 'if'.");
    expression();
    consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");

    int thenJump = emitJump(OP_JUMP_IF_FALSE);
    emitByte(OP_POP);
    statement();
    int elseJump = emitJump(OP_JUMP);
    patchJump(thenJump);
    emitByte(OP_POP);
    if (match(TOKEN_ELSE)) statement();
    patchJump(elseJump);
}

static void printStatement() {
    expression();
    consume(TOKEN_SEMICOLON, "Expect ';' after value.");
    emitByte(OP_PRINT);
}

static void returnStatement() {
    if (current->type == TYPE_SCRIPT) {
        error("Cannot return from top-level code.");
    }
    if (match(TOKEN_SEMICOLON)) {
        emitReturn();
    } else {
        if (current->type == TYPE_INITIALIZER) {
            error("Cannot return value from initializer.");
        }
        expression();
        consume(TOKEN_SEMICOLON, "Expect ';' after return value.");
        emitByte(OP_RETURN);
    }
}

static void whileStatement() {
    int loopStart = currentChunk()->count;
    consume(TOKEN_LEFT_PAREN, "Expect '(' after 'while'.");
    expression();
    consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");
    int exitJump = emitJump(OP_JUMP_IF_FALSE);
    emitByte(OP_POP);
    statement();
    emitLoop(loopStart);
    patchJump(exitJump);
    emitByte(OP_POP);
}

static void synchronize() {
    parser.panicMode = false;
    while (parser.current.type != TOKEN_EOF) {
        if (parser.previous.type == TOKEN_SEMICOLON) return;
        switch (parser.current.type) {
            case TOKEN_CLASS:
            case TOKEN_DEF:
            case TOKEN_VAR:
            case TOKEN_FOR:
            case TOKEN_IF:
            case TOKEN_WHILE:
            case TOKEN_PRINT:
            case TOKEN_RETURN: return;
            default:;
        }
        advance();
    }
}

static void declaration() {
    if (match(TOKEN_CLASS)) {
        classDeclaration();
    } else if (match(TOKEN_DEF)) {
        funcDeclaration();
    } else if (match(TOKEN_VAR)) {
        varDeclaration();
    } else {
        statement();
    }
    if (parser.panicMode) synchronize();
}

static void statement() {
    if (match(TOKEN_PRINT)) {
        printStatement();
    } else if (match(TOKEN_IF)) {
        ifStatement();
    } else if (match(TOKEN_RETURN)) {
        returnStatement();
    } else if (match(TOKEN_WHILE)) {
        whileStatement();
    } else if (match(TOKEN_FOR)) {
        forStatement();
    } else if (match(TOKEN_LEFT_BRACE)) {
        beginScope();
        block();
        endScope();
    } else {
        expressionStatement();
    }
}

ObjFunction* compile(const char* source) {
    initScanner(source);
    Compiler compiler;
    initCompiler(&compiler, TYPE_SCRIPT);
    parser.hadError = false;
    parser.panicMode = false;
    advance();
    while (!match(TOKEN_EOF)) {
        declaration();
    }
    ObjFunction* function = endCompiler();
    return parser.hadError ? NULL : function;
}

void markCompilerRoots() {
    Compiler* compiler = current;
    while (compiler != NULL) {
        markObject((Obj*)compiler->function);
        compiler = compiler->enclosing;
    }
}