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From: jeenglis@nunki.usc.edu (Joe English)
Newsgroups: comp.lang.c
Subject: Re: evaluating math w/o recompile
Message-ID: <5124@merlin.usc.edu>
Date: 17 Sep 89 06:44:27 GMT
References: <11068@smoke.BRL.MIL> <225800223@uxe.cso.uiuc.edu>
Sender: news@merlin.usc.edu
Reply-To: jeenglis@nunki.usc.edu (Joe English)
Organization: University of Southern California, Los Angeles, CA
Lines: 42

zador-anthony@CS.YALE.EDU (anthony zador) writes:
>I would like to be able to specify the form of the function f
>at *run time* (no recompiles). That is, i would like 
>to place a line of math
>in some file and have the program read it in and evaluate it.

How about writing a set of math interface 
functions that take, instead of a fixed set of parameters,
an argv/argc pair?  I'm doing something like that right
now in a report generator I'm writing:

enum valuetype {  vInt, vFloat, vString ... };

typedef struct {
   enum valuetype tag;
   union {
      int ival;
      double fval;
      char *sval;
      ...
   } datum;
} value;


Then for the interface function:

value somefunc(int argc,value *argv)

{
    /* use argc parameters from the argv array.  Type-checking
       of arguments is done by the parser & function
       lookup table.
    */
}

If you don't need full generality, you can use
'double *argv'.


--Joe English

  jeenglis@nunki.usc.edu