Re: Parsing / Lexing question & P-code

Hi,


We are currently working on a compiler for a Pascal like language with
a lot of OOP extensions using plain C++. We haven't used a parser
generator but wrote all of the parsing code ourselves. Our grammar
dictates the following for the assignment statement:


Assignment ::= RefExpression [AssignOp Expression]


RefExpression is an expression that can be assigned to. It's defined
as follows:


RefExpression ::= ['&'] SelValue {'.' SelValue}
SelValue ::= RefName {AccessSpec}
AccessSpec ::= ArrayAccess | MethodInvocation | PointerDeref
ArrayAccess ::= '[' ExpressionList ']'
MethodInvocation ::= '(' [Expression] {',' [Expression]} ')'
PointerDeref ::= '^'


Ignore the ['&'] ater RefExpression, it's a language enhancement.


The parser will get the name from the scanner and look up the
definition of this name. If it is a method and the following is a '(',
the appropriate functions are called. The question whether the
expression is indeed assignable is done at the end if it finds an ':='
token. All this is necessary because all of the following must
compile:


f := 12;
a[12] := 12;
p^ := 5;
g^ := 15;


where f is an integer variable, a is an array of integers variable, p
is a pointer to an integer, and g is a function that returns an
integer.


HTH,


Sebastian Moleski


P.S. If you are interested in an extended development of a compiler of
a pascal-like language, please contact me. It's a non-profit project
which will probably go open source as soon as something presentable is
done. Already, there's a strong code base handling type definitions,
constant expressions, qualified names, classes, and a lot of other
nifty language constructs. The compiler is written entirely in C++
with a lot of classes and some templates. Hope you're interested.


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