[Kranar]

Strictly speaking, D is not context free nor is any statically typed programming language. That said most languages, including D, have supersets that are context free and can be used to build an AST which can then be refined further with context sensitive checks (ie. variables are used after declaration) and then even further with type checks.

Many language tools don't need a full blown language parser and can get by with a context-free parser for the language's superset. Things like autocompletion, spell checking, documentation/highlighting can all be implemented using context-free parsers.

[WalterBright]

I suppose we could argue about the definition of context free, but the compiler lexes it without any reference to the parser, and the parser builds the AST without any reference to symbols or semantic meaning.

> spell checking ... using context-free parsers

Only up to a point. D's spell checker uses the symbols in scope as its "dictionary". This means it is very good at guessing what you meant instead of what is typed, as the dictionary is very targeted. I.e. it uses the context, and the spell checker is part of the semantic pass.

[Kranar]

A context free grammar has a formal and rigorous definition. One way to see that Dlang does not have a strictly context free grammar for its AST is the following snippet of code:

A[B] C;

That is parsed differently depending on whether B is a constant integer expression in which case it parses to the declaration of an array of type A with a size of B, or whether B is a typename in which case it parses into an hash map with keys of type B and values of type A.

This disambiguation can not be specified by the context free grammar and instead must be delayed until the semantic analysis (which is usually defined by a context sensitive grammar).

Pretty much all statically typed languages work this way with various kinds of ambiguities. In practice, it's not a particularly big deal. But that's kind of my point, there's no need to work exceedingly hard to force a language construct to be context free, especially if making it context free results in a lack of readability or awkward syntax.

It's perfectly fine to specify a superset of the language that is context free, parse an AST for the superset of that language and then resolve AST ambiguities in later phases, such as the semantic analysis phase or the type checking phase. Almost any tool written to assist an IDE with autocompletion or other functionality will have no problem working with the language superset.

[WalterBright]

> That is parsed differently

It isn't parsed differently. Its semantic meaning depends on what B is, but not the parse.

[kingaillas]

You realize the poster you are responding to is the creator of D? And has spend his career writing compilers? I'm not sure he needs to have someone explain what a context free grammar is.

[Kranar]

I understand you wish to flatter WalterBright, but please note that your comment is fairly toxic and not well suited to Hacker News. Please stay on topic and feel free to contribute to the points being made. This kind of hero worship often just degrades discussion and is better left to other forms of social media.

[throwaway_pdp09]

Yours is the toxic comment. Appeal to authority is fine if the authority is an authority and WB has proven his. Suggestions of intention to flatter and accusations of hero worship are pretty gross. @kingaillas's point is entirely valid IMO.