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#include "parser.h"
#include <stdio.h>
struct ast *parse(enum parser_status *status, struct lexer *lexer)
{
struct token t = lexer_peek(lexer);
*status = PARSER_OK;
if (t.type == TOKEN_EOF)
{
lexer_pop(lexer);
return NULL;
}
else
{
struct ast *exp = parse_exp(status, lexer);
if (*status != PARSER_OK)
{
return NULL;
}
struct token t = lexer_pop(lexer);
if (*status == PARSER_OK && t.type == TOKEN_EOF)
{
return exp;
}
else if (t.type != TOKEN_EOF)
{
*status = PARSER_UNEXPECTED_TOKEN;
fprintf(stderr, "parser: unexpected token\n");
}
ast_free(exp);
return NULL;
}
}
struct ast *parse_exp(enum parser_status *status, struct lexer *lexer)
{
struct ast *left = parse_sexp(status, lexer);
if (*status == PARSER_UNEXPECTED_TOKEN)
return NULL;
struct token t = lexer_peek(lexer);
if (t.type != TOKEN_PLUS && t.type != TOKEN_MINUS)
{
*status = PARSER_OK;
return left;
}
else
{
struct ast *root = left;
do
{
left = root;
t = lexer_pop(lexer);
if (t.type == TOKEN_PLUS)
root = ast_new(AST_PLUS);
else
root = ast_new(AST_MINUS);
root->left = left;
root->right = parse_sexp(status, lexer);
if (*status == PARSER_UNEXPECTED_TOKEN)
{
ast_free(root);
return NULL;
}
t = lexer_peek(lexer);
} while (t.type != TOKEN_EOF
&& (t.type == TOKEN_PLUS || t.type == TOKEN_MINUS));
return root;
}
}
struct ast *parse_sexp(enum parser_status *status, struct lexer *lexer)
{
struct ast *left = parse_texp(status, lexer);
if (*status == PARSER_UNEXPECTED_TOKEN)
return NULL;
struct token t = lexer_peek(lexer);
if (t.type != TOKEN_MUL && t.type != TOKEN_DIV)
{
*status = PARSER_OK;
return left;
}
else
{
struct ast *root = left;
do
{
left = root;
t = lexer_pop(lexer);
if (t.type == TOKEN_MUL)
root = ast_new(AST_MUL);
else
root = ast_new(AST_DIV);
root->left = left;
root->right = parse_texp(status, lexer);
if (*status == PARSER_UNEXPECTED_TOKEN)
{
ast_free(root);
return NULL;
}
t = lexer_peek(lexer);
} while (t.type != TOKEN_EOF
&& (t.type == TOKEN_MUL || t.type == TOKEN_DIV));
return root;
}
}
struct ast *parse_texp(enum parser_status *status, struct lexer *lexer)
{
struct token t = lexer_pop(lexer);
if (t.type == TOKEN_NUMBER)
{
struct ast *res = ast_new(AST_NUMBER);
res->value = t.value;
return res;
}
else if (t.type == TOKEN_MINUS)
{
t = lexer_peek(lexer);
if (t.type != TOKEN_NUMBER && t.type != TOKEN_LEFT_PAR)
{
*status = PARSER_UNEXPECTED_TOKEN;
fprintf(stderr, "parser: unexpected token\n");
return NULL;
}
struct ast *unary = ast_new(AST_NEG);
unary->left = parse_texp(status, lexer);
return unary;
}
else if (t.type == TOKEN_LEFT_PAR)
{
struct ast *exp = parse_exp(status, lexer);
t = lexer_pop(lexer);
if (t.type != TOKEN_RIGHT_PAR)
{
*status = PARSER_UNEXPECTED_TOKEN;
fprintf(stderr, "parser: expected closing parenthesis\n");
ast_free(exp);
return NULL;
}
return exp;
}
else
{
*status = PARSER_UNEXPECTED_TOKEN;
fprintf(stderr, "parser: unexpected token\n");
return NULL;
}
}
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