Where is "require" defined?

Question

I have been looking in Rakudo source for the implementation of require, first out of curiosity and second because I wanted to know if it was returning something.

I looked up sub require and it returned this hit, which actually seems to be the source for require, but it's called sub REQUIRE_IMPORT. It returns Nil and is declared as such, which pretty much answers my original question. But now my question is: Where's the mapping from that sub to require? Is it really the implementation for that function? Are there some other functions that are declared that way?

Answer 1

require is not a sub, but rather a statement control (so, in the same category of things like use, if, for, etc.) It is parsed by the Perl 6 grammar and there are a few different cases that are accepted. It is compiled in the Perl 6 actions, which has quite a bit to handle.

Much of the work is delegated to the various CompUnit objects, which are also involved with use/need. It also has to take care of stubbing symbols that the require will bring in, since the set of symbols in a given lexical scope is fixed at compile time, and the REQUIRE_IMPORT utility sub is involved with the runtime symbol import too.

The answer to your question as to what it will evaluate to comes at the end of the method:

    $past.push($<module_name>
               ?? self.make_indirect_lookup($longname.components())
               !! $<file>.ast);

Which means:

• If it was a require Some::Module then evaluate to a lookup of Some::Module
• If it was a require $file style case, evaluate to the filename