PC_graph/parser.c

#include <stdlib.h>
#include <stdio.h>
#include "parser.h"

static int token_is(struct lexer *lex, enum token_type type) {
    return lex_token(lex)->type == type;
}

static int accept(struct lexer *lex, enum token_type type) {
    if (token_is(lex, type)) {
        lex_next(lex);
        return 1;
    }
    return 0;
}

static double token_num(struct lexer *lex) {
    return lex_token(lex)->val.num;
}

static enum math_fn token_fn(struct lexer *lex) {
    return lex_token(lex)->val.fn;
}

static void error_expected_one_of(struct lexer *lex, const int expected[], enum token_type got) {
    static const char* token_name[] = {
        "end of expression",
        "lexer error",
        "constant",
        "+",
            "-",
            "*",
            "/",
            "^",
            "x",
            "function name",
            "(",
            ")"
    };

    int separate = 0;

    fprintf(stderr, "Syntax error - expected ");

    for (; *expected >= 0; ++expected) {
        if (separate)
            fprintf(stderr, ", ");
        else
            separate = 1;

        fprintf(stderr, "'%s'", token_name[*expected]);
    }

    fprintf(stderr, " - but got '%s'\n", token_name[got]);

    lex_print_position(lex);
}

static void error_expected_single(struct lexer* lex, enum token_type expected, enum token_type got) {
    static int expected_arr[] = { -1, -1 };
    expected_arr[0] = expected;
    error_expected_one_of(lex, expected_arr, got);
}

struct expr_node* parse_subexpression(struct lexer* lex);

static struct expr_node* parse_bracketed(struct lexer* lex) {
    struct expr_node* node;

    if (!accept(lex, TOK_LEFT_PAREN)) {
        error_expected_single(lex, TOK_LEFT_PAREN, lex_token(lex)->type);
        return NULL;
    }

    if (!(node = parse_subexpression(lex)))
        return NULL;

    if (!accept(lex, TOK_RIGHT_PAREN)) {
        error_expected_single(lex, TOK_RIGHT_PAREN, lex_token(lex)->type);
        node_free(node);
        return NULL;
    }

    return node;
}

static struct expr_node* parse_base(struct lexer* lex) {
    struct expr_node* inner;

    if (token_is(lex, TOK_NUMBER)) {
        double val = token_num(lex);
        lex_next(lex);
        return node_create_const(val);
    }

    if (accept(lex, TOK_X)) {
        return node_create_x();
    }

    if (token_is(lex, TOK_FUNCTION)) {
        enum math_fn fn = token_fn(lex);
        lex_next(lex);

        if (!(inner = parse_bracketed(lex)))
            return NULL;

        return node_create_fn(fn, inner);
    }

    if (token_is(lex, TOK_LEFT_PAREN)) {
        return parse_bracketed(lex);
    }

    {
        static const int expected[] = { TOK_NUMBER, TOK_X, TOK_FUNCTION, TOK_LEFT_PAREN, -1 };
        error_expected_one_of(lex, expected, lex_token(lex)->type);
    }

    return NULL;
}

static struct expr_node* parse_unary(struct lexer* lex);

static struct expr_node* parse_factor(struct lexer* lex) {
    struct expr_node* node, * new_node, * inner;

    if (!(node = parse_base(lex)))
        return NULL;

    if (accept(lex, TOK_POWER)) {
        if (!(inner = parse_unary(lex))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = node_create_pow(node, inner))) {
            node_free(node);
            node_free(inner);
            return NULL;
        }

        return new_node;
    }

    return node;
}

static struct expr_node* parse_unary(struct lexer *lex) {
    if (accept(lex, TOK_MINUS)) {
        struct expr_node *node, *inner;
        
        if (!(inner = parse_factor(lex)))
            return NULL;

        if (!(node = node_create_neg(inner))) {
            node_free(inner);
            return NULL;
        }

        return node;
    }

    accept(lex, TOK_PLUS);
    return parse_factor(lex);
}

static struct expr_node *parse_term(struct lexer *lex) {
    struct expr_node *node, *new_node, *inner;

    if (!(node = parse_unary(lex)))
        return NULL;

    while (1) {
        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);

        if (accept(lex, TOK_MULTIPLY))
            create_node = node_create_mult;
        else if (accept(lex, TOK_DIVIDE))
            create_node = node_create_div;
        else
            break;

        if (!(inner = parse_unary(lex))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = create_node(node, inner))) {
            node_free(node);
            node_free(inner);
            return NULL;
        }

        node = new_node;
    }

    return node;
}

struct expr_node *parse_subexpression(struct lexer *lex) {
    struct expr_node *node, *new_node, *inner;
    
    /*
    if (accept(lex, TOK_MINUS)) {
        if (!(term = parse_term(lex)))
            return NULL;

        if (!(node = node_create_neg(term))) {
            node_free(term);
            return NULL;
        }
    }
    else {
        accept(lex, TOK_PLUS);

        if (!(node = parse_term(lex)))
            return NULL;
    }
    
    */

    if (!(node = parse_term(lex)))
        return NULL;

    while (1) {
        struct expr_node *(*create_node)(struct expr_node *left, struct expr_node *right);

        if (accept(lex, TOK_PLUS))
            create_node = node_create_add;
        else if (accept(lex, TOK_MINUS))
            create_node = node_create_sub;
        else
            break;

        if (!(inner = parse_term(lex))) {
            node_free(node);
            return NULL;
        }

        if (!(new_node = create_node(node, inner))) {
            node_free(node);
            node_free(inner);
            return NULL;
        }

        node = new_node;
    }

    return node;
}

struct expr_node *parse_expression(struct lexer *lex) {
    struct expr_node *node;

    if (!(node = parse_subexpression(lex)))
        return NULL;

    if (!token_is(lex, TOK_EOF)) {
        error_expected_single(lex, TOK_EOF, lex_token(lex)->type);
        node_free(node);
        return NULL;
    }

    return node;
}