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           *
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  17  * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE FOR ANY        *
  18  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES  *
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  20  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER  *
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  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, len = strlen(s);
  44         bool isnum = true;
  45
  46         for(i = 0; isnum && i < len; ++i)
  47                 if(!isdigit(s[i]) && s[i] != '.') isnum = false;
  48
  49         // caveat: if length is one and that's just a dot, then it's NOT a number.
  50         if(isnum && len == 1 && *s == '.')
  51                 isnum = false;
  52
  53         return isnum;
  54 }
  55
  56 //! Evaluates a token on the calculator.
  57 /**
  58  * @param calculator The calculator.
  59  * @param tok The token.
  60  */
  61 static void evalToken(RPNCalculator *calculator, char *tok)
  62 {
  63         RPNVariable *var;
  64         bool executed;
  65
  66         // try to execute an operator; if that fails, then try to execute a command
  67         executed = RPN_executeOperator(calculator, tok) ||
  68                    RPN_executeCommand(calculator, tok);
  69
  70         // no? then treat this as a variable name.
  71         if(!executed)
  72         {
  73                 // find variable with this name
  74                 var = RPN_findVariable(calculator->variables, tok);
  75
  76                 // if found,
  77                 if(var)
  78                         // push it's value to the stack
  79                         RPN_push(calculator->stack, var->value);
  80                 else
  81                         // add a new variable to the variable table, whose value is that of
  82                         // the topmost item in the stack.
  83                         RPN_addVariable(calculator->variables, strdup(tok),
  84                                         RPN_peek(calculator->stack));
  85         }
  86 }
  87
  88 //! Evaluates a string on a calculator.
  89 /**
  90  * @param s The string to evaluate.
  91  * @param calculator The calculator on which to evaluate.
  92  * @return The topmost item of the calculator's stack.
  93  */
  94 RPNValue RPN_eval(char *s, RPNCalculator *calculator)
  95 {
  96         /* these are just used as shorthands to make the code more readable. */
  97         RPNTokens *tokens;
  98         char *token;
  99
 100         /* split the string. */
 101         tokens = calculator->tokens = RPN_splitString(s);
 102
 103         /* go through the tokens. */
 104         for(tokens->pos = 0; tokens->pos < tokens->size; ++tokens->pos)
 105         {
 106                 token = tokens->tokens[tokens->pos];
 107                 /* push numeric tokens to the stack. */
 108                 if(isNumber(token))
 109                         RPN_push(calculator->stack, RPN_strtod(token, NULL));
 110                 /* delegate other tokens to evalToken(). */
 111                 else
 112                         evalToken(calculator, token);
 113         }
 114
 115         /* cleanup. */
 116         RPN_freeTokens(tokens);
 117         calculator->tokens = NULL;
 118
 119         return RPN_peek(calculator->stack);
 120 }