src/parser.c

   1 /*******************************************************************************
   2  * Reverse Polish Notation calculator.                                         *
   3  * Copyright (c) 2007-2008, Samuel Fredrickson <kinghajj@gmail.com>            *
   4  * All rights reserved.                                                        *
   5  *                                                                             *
   6  * Redistribution and use in source and binary forms, with or without          *
   7  * modification, are permitted provided that the following conditions are met: *
   8  *     * Redistributions of source code must retain the above copyright        *
   9  *       notice, this list of conditions and the following disclaimer.         *
  10  *     * Redistributions in binary form must reproduce the above copyright     *
  11  *       notice, this list of conditions and the following disclaimer in the   *
  12  *       documentation and/or other materials provided with the distribution.  *
  13  *                                                                             *
  14  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER ``AS IS'' AND ANY EXPRESS *
  15  * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED           *
  16  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE      *
  17  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY        *
  18  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES  *
  19  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR          *
  20  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER  *
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  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY   *
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH *
  24  * DAMAGE.                                                                     *
  25  ******************************************************************************/
  26
  27 /*******************************************************************************
  28  * parser.c - parses RPN expressions.                                          *
  29  ******************************************************************************/
  30
  31 #include <ctype.h>
  32 #include "rpn.h"
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 //! Tests if a string can be converted into a number.
  37 /**
  38  * @param s The string to test.
  39  * @return true or false.
  40  */
  41 static bool isNumber(char *s)
  42 {
  43         size_t i = 0, len = strlen(s);
  44         bool isnum = true;
  45
  46         if(len && s[0] == '-')
  47         {
  48                 // if it's just a dash, it's not a number.
  49                 if(len == 1)
  50                         isnum = false;
  51                 else
  52                         i = 1;
  53         }
  54
  55         for(; isnum && i < len; ++i)
  56                 if(!isdigit(s[i]) && s[i] != '.') isnum = false;
  57
  58         // caveat: if length is one and that's just a dot, then it's NOT a number.
  59         if(isnum && len == 1 && *s == '.')
  60                 isnum = false;
  61
  62         return isnum;
  63 }
  64
  65 //! Evaluates a token on the calculator.
  66 /**
  67  * @param calculator The calculator.
  68  * @param tok The token.
  69  */
  70 static void evalToken(RPNCalculator *calculator, char *tok)
  71 {
  72         RPNStack *stack = RPN_currentStack(calculator);
  73         RPNVariable *var;
  74         bool executed;
  75
  76         // try to execute an operator; if that fails, then try to execute a command
  77         executed = RPN_executeOperator(calculator, tok) ||
  78                    RPN_executeCommand(calculator, tok);
  79
  80         // no? then treat this as a variable name.
  81         if(!executed)
  82         {
  83                 // find variable with this name
  84                 var = RPN_findVariable(calculator->variables, tok);
  85
  86                 // if found,
  87                 if(var)
  88                         // push it's value to the stack
  89                         RPN_push(stack, var->value);
  90                 else
  91                         // add a new variable to the variable table, whose value is that of
  92                         // the topmost item in the stack.
  93                         RPN_addVariable(calculator->variables, strdup(tok),
  94                                         RPN_peek(stack));
  95         }
  96 }
  97
  98 //! Evaluates a string on a calculator.
  99 /**
 100  * @param s The string to evaluate.
 101  * @param calculator The calculator on which to evaluate.
 102  * @return The topmost item of the calculator's stack.
 103  */
 104 RPNValue RPN_eval(char *s, RPNCalculator *calculator)
 105 {
 106         /* these are just used as shorthands to make the code more readable. */
 107         RPNTokens *tokens;
 108         char *token;
 109
 110         /* split the string. */
 111         tokens = calculator->tokens = RPN_splitString(s);
 112
 113         /* go through the tokens. */
 114         for(tokens->pos = 0; tokens->pos < tokens->size; ++tokens->pos)
 115         {
 116                 token = tokens->tokens[tokens->pos];
 117                 /* push numeric tokens to the stack. */
 118                 if(isNumber(token))
 119                         RPN_push(RPN_currentStack(calculator), RPN_strtod(token, NULL));
 120                 /* delegate other tokens to evalToken(). */
 121                 else
 122                         evalToken(calculator, token);
 123         }
 124
 125         /* cleanup. */
 126         RPN_freeTokens(tokens);
 127         calculator->tokens = NULL;
 128
 129         if(calculator->needs_newline) {
 130                 RPN_printf("\n");
 131                 calculator->needs_newline = false;
 132         }
 133
 134         return RPN_peek(RPN_currentStack(calculator));
 135 }