Re: Using the "output" from yacc

[Hans Aberg]

On 27 Jan 2009, at 01:14, Alex Ryu wrote:

> I have a series of large arrays of floating point data.  "Attached"  
> to each
> array is a smaller array of integers, call it c.   What I would like  
> to do
> is perform operations on c of this nature:
> if c[1] < 54 and c[13] != 7 then c[3] = 16, etc.  These instructions  
> will be
> contained in a char buffer, which I think I can use as the input to  
> lex.
> After the operations are made, then I just want to output/write to  
> disk the
> arrays.  Is this possible using lex and bison?  It seems like it  
> should be,
> but I can't quite find a way.  How do I make yyparse() "see" the  
> arrays?
> Would I have to directly modify the output of bison?  Thanks for any  
> help
> you can provide.
> Outline:
> Say c = {1,3,5,9,-8}, and instructs = "if c[1] < 54 and c[0] != 7  
> then c[3]
> = 16"  Then I would want yyparse() to change c to {1,3,5,16,-8}.   
> Remember
> that we have a lot of "c's", so I suppose one would make the  
> substitution 1
> for c[0], etc, before passing to yylex().

Bison and Flex are used to construct compilers/interpreters, from a  
small calculators as in the Bison manual, to full grown computer  
languages.

Why can't or would not want you use a for an existing language, like C/ 
C++, or Hugs or GHC for a language like Haskell <http://haskell.org>  
which admit FFI (Foreign Function Interfaces) - that might save you  
time, even if you want to take the long road of constructing.

Otherwise, external is typically called from the actions - so you make  
sure your .y file ha a #include to your code header, and inserts the  
actions into the headers. If you want to be able to do definitions,  
make a lookup table that the lexer can see. If you want to do loops  
and code jumps, build closures that can be executed after the parsing.

  Hans