CODEWITHSUNDEEP
parsingprogramming-languagesgrammartheory
Adam Lee
Adam Lee

Reputation: 25738

Are the grammars of modern programming languages context-free or context-sensitive?

Are the C++, C# or Java languages context-free or context-sensitive?

Upvotes: 12

Views: 4934

Answers (1)

templatetypedef
templatetypedef

Reputation: 372724

C++ is neither context-free nor context-sensitive, since the template system is Turing-complete and determining whether a piece of C++ code is legal C++ is undecidably hard. For example, I could define a template class that simulates a TM on a string and then creates a constant with value 1 if the machine accepts and 0 if it does not. If I did that, then the following code would be legal iff the TM halted on the given input:

int myArray[TMTemplate</* ... args ... */>::value];

Since if the TM rejects, this creates an array of size 0, which is not allowed.

Neither C# nor Java is context-free, because checking of whether a variable is used correctly and consistently throughout a particular scope is known not to be context-free (the proof is complex and relies on Ogden's lemma). However, I'm not sure whether or not they are context-sensitive.

Hope this gives a partial answer to your questions!

Upvotes: 8

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