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Old 03-10-2007, 11:47 AM   #1
unreal07
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Registered: Mar 2007
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Using Flex and Bison to parse the variable declaration section in Pascal


Hi everyone, I'm undertaking a project to convert Pascal to ARM assembler using Flex and Bison with C++. I have a problem when attempting to add variable information to a symbol table. The problem is as follows:

In Pascal, when a variable is declared, the TYPE of the variable follows the actual identifier e.g.

VAR a,b : int;

When my parser interprets this line, it cannot tell that "a" and "b" are integers until it reaches the end of the line. So, when adding to my symbol table, I must use some sort of temporary store to save a list of identifiers encountered before the end of the line, at which point I finally know the TYPE of variable, and it can be added to the symbol table.

The grammar I am using is as follows:

D -> L : T (Variable declaration)
T -> identifier (The TYPE i.e. integer, char or user defined type)
L -> L , identifier | identifier (list of variables)

I was wondering if there is a better method of solving this problem, for example changing the underlying grammar rules, rather than implementing an extra data structure to temporarily store the variable names.

Thanks in advance,

M
 
Old 03-10-2007, 08:25 PM   #2
jlinkels
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It is looooooooong time ago that I remotely understood wat YACC (Bison now) did. But I am sure that there are YACC scripts available for the Pascal language. Why not start from there?

jlinkels
 
  


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