clox/parser.c

#include "parser.h"

Expr* Expression(void);
Expr* Equality(void);
Expr* Comparison(void);
Expr* Term(void);
Expr* Factor(void);
Expr* Unary(void);
Expr* Primary(void);
int Match(int, ...);
int Check(TokenType);
int ParserAtEnd(void);
Token* ParserPeek(void);
Token* Previous(void);
Token* AdvanceParser(void);

const TokenList* ListOfTokens;
int Current = 0;

Expr* GenerateExpressionTree(const TokenList* list) {
    ListOfTokens = list;

    return Expression();
}

//Simply expands the equality rule
Expr* Expression() {
    return Equality();
}

Expr* Equality() {
    Expr* expr = Comparison();

    while(Match(2, Bang_Equal, Equal_Equal)) {
        Token* operator = Previous();
        Expr* right = Comparison();
        Expr* temp = calloc(1, sizeof(Expr));
        temp->type = BINARY;
        temp->expression.Binary.left = expr;
        temp->expression.Binary.op = operator;
        temp->expression.Binary.right = right;
        expr = temp;
    }

    return expr;
}

Expr* Comparison() {
    Expr* expr = Term();

    while(Match(4, Greater, Greater_Equal, Less, Less_Equal)) {
        Token* operator = Previous();
        Expr* right = Term();
        Expr* temp = calloc(1, sizeof(Expr));
        temp->type = BINARY;
        temp->expression.Binary.left = expr;
        temp->expression.Binary.op = operator;
        temp->expression.Binary.right = right;
        expr = temp;
    }

    return expr;
}

Expr* Term() {
    Expr* expr = Factor();

    while(Match(2, Minus, Plus)) {
        Token* operator = Previous();
        Expr* right = Factor();
        Expr* temp = calloc(1, sizeof(Expr));
        temp->type = BINARY;
        temp->expression.Binary.left = expr;
        temp->expression.Binary.op = operator;
        temp->expression.Binary.right = right;
        expr = temp;
    }

    return expr;
}

Expr* Factor() {
    Expr* expr = Unary();

    while(Match(2, Slash, Star)) {
        Token* operator = Previous();
        Expr* right = Unary();
        Expr* temp = calloc(1, sizeof(Expr));
        temp->type = BINARY;
        temp->expression.Binary.left = expr;
        temp->expression.Binary.op = operator;
        temp->expression.Binary.right = right;
        expr = temp;
    }

    return expr;
}

Expr* Unary() {
    if (Match(2, Bang, Minus)) {
        Token* operator = Previous();
        Expr* right = Unary();
        Expr* expr = calloc(1, sizeof(Expr));
        expr->type = UNARY;
        expr->expression.Unary.op = operator;
        expr->expression.Unary.right = right;
        return expr;
    }

    return Primary();
}

Expr* Primary() {
    Expr* expr = calloc(1, sizeof(Expr));
    expr->type = LITERAL;

    if (Match(3, FALSE, TRUE, NIL)) {
        expr->expression.Literal.type = ParserPeek();//CreateToken("false", FALSE);
        return expr;
    }
    // if (SMatch(1, TRUE)) {
    //     expr->expression.Literal.type = //CreateToken("true", TRUE);
    //     return expr;
    // }
    // if (SMatch(1, NIL)) {
    //     expr->expression.Literal.type = //CreateToken("nil", NIL);
    //     return expr;
    // }

    if (Match(2, Number, String)) {
        expr->expression.Literal.type = Previous();
        return expr;
    }

    if (Match(1, LParen)) {
        free(expr);
        expr = Expression();
        //Consume(RParen, "Expect ')' after expression.");
        expr->type = GROUPING;
        return expr;
    }

    return expr;
}

int Match(int count, ...) {
    va_list list;
    va_start(list, count);

    for(int i = 0; i < count; i++) {
        if(Check(va_arg(list, TokenType))) {
            AdvanceParser();
            return 1;
        }
    }

    return 0;
}

int Check(TokenType type) {
    if (ParserAtEnd()) return 0;
    return ParserPeek()->type == type;
}

int ParserAtEnd() {
    return ParserPeek()->type == EndOF;
}

Token* ParserPeek() {
    return ListOfTokens->tokens[Current];
}

Token* Previous() {
    return ListOfTokens->tokens[Current - 1];
}

Token* AdvanceParser() {
    if (!ParserAtEnd()) Current++;

    return Previous();
}

void PrintExpressionTree(const Expr* tree) {

}

void FreeExpressionTree(Expr* tree) {
    if (!tree) return;

    if (tree->type == BINARY) {
        FreeExpressionTree(tree->expression.Binary.left);
        FreeExpressionTree(tree->expression.Binary.right);
        //FreeToken(tree->expression.Binary.op);
    }
    else if (tree->type == UNARY) {
        FreeExpressionTree(tree->expression.Unary.right);
        //FreeToken(tree->expression.Unary.op);
    }
    //else if (tree->type == LITERAL) FreeToken(tree->expression.Literal.type);

    free(tree);
}