CODEWITHSUNDEEP
parsingcompiler-construction
Shane Lu
Shane Lu

Reputation: 1114

Are the compilers of C++ written using a lexer/parser generator?

(Background: Inspired by Is C++ context-free or context-sensitive?, while I am writing a simple compiler using jflex/cup myself. )

If they are written using a lexer/parser generator, how do we specify the grammar?

Since code like 

a b(c);

could be interpreted as either a function declaration or a local variable definition, how could we handle it in the grammar definition file?

Another example could be the token ">>" in the following code:

std::vector<std::vector<int>> foo;
int a = 1000 >> 4;

Thanks

Upvotes: 0

Views: 414

Answers (1)

J&#246;rg W Mittag
J&#246;rg W Mittag

Reputation: 369594

Are the compilers of C++ written using a lexer/parser generator?

It depends. Some are, some aren't.

GCC originally did use GNU bison, but was re-written a couple of years ago with a hand-written parser. If I have understood that correctly, the main reason was that writing the parser by hand gives you more control over the parser state, and specifically, how much "extraneous" data to keep in there, so that you can generate better error messages.

If they are written using a lexer/parser generator, how do we specify the grammar?

This depends on which parser generator you are using.

Since code like 

a b(c);

could be interpreted as either a function declaration or a local variable definition, how could we handle it in the grammar definition file?

Some parser generators may be powerful enough to handle this directly.

Some aren't. Some parser generators which aren't powerful enough have a concept of semantic action that allow you to attach code written in an arbitrarily powerful language to parser rules. E.g. yacc allows you to attach C code to rules.

Otherwise, you will have to handle it during semantic analysis.

Upvotes: 4

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