/*
** Extended calculator grammar — adds exponentiation (^) to the base four
** operations.
**
** Token codes match the base grammar (calc.lime) exactly for the first
** seven tokens.  CARET is appended as token code 8.
*/

%name CalcPower
%token_type {int}
%type expr {int}
%extra_argument {int *result}

%include {
#include <stdio.h>
#include <assert.h>

/*
** Integer exponentiation by repeated squaring.
*/
static int int_pow(int base, int exp) {
    if (exp < 0) return 0;
    int result = 1;
    while (exp > 0) {
        if (exp & 1) result *= base;
        base *= base;
        exp >>= 1;
    }
    return result;
}
}

%syntax_error {
    (void)yymajor;
    (void)yyminor;
    fprintf(stderr, "syntax error\n");
    *result = 0;
}

/* Tokens — same order as calc.lime, with CARET appended */
%token PLUS.
%token MINUS.
%token TIMES.
%token DIVIDE.
%token LPAREN.
%token RPAREN.
%token INTEGER.
%token CARET.

/* Precedence (lowest to highest) */
%left PLUS MINUS.
%left TIMES DIVIDE.
%right CARET.
%right UMINUS.

%start_symbol program

program ::= expr(A). { *result = A; }

expr(A) ::= expr(B) PLUS expr(C).     { A = B + C; }
expr(A) ::= expr(B) MINUS expr(C).    { A = B - C; }
expr(A) ::= expr(B) TIMES expr(C).    { A = B * C; }
expr(A) ::= expr(B) DIVIDE expr(C).   {
    if (C == 0) {
        fprintf(stderr, "division by zero\n");
        A = 0;
    } else {
        A = B / C;
    }
}
expr(A) ::= expr(B) CARET expr(C).    { A = int_pow(B, C); }
expr(A) ::= MINUS expr(B). [UMINUS]   { A = -B; }
expr(A) ::= LPAREN expr(B) RPAREN.    { A = B; }
expr(A) ::= INTEGER(B).               { A = B; }