Monday, May 12, 2008

Type-Inference - Part 1


I finally got to a point where I can start the fun challenging aspects involved in the new languages. Smart type inference. I'm just posting a few notes about it for others to either laugh about or reply to. First I'll start with Lambda expressions and how to properly discern a good match from a not-so-good match.

Figure 1

Basically a lambda signature type, if encountered as a parameter of a call, shall yield explicit or implicit Tn elements and a Tr element for the result. Each signature will only match with a relative RoughSignatureMatch (see: Fig. 1) series if the delegate type assigned has the same parameter count, some or all of the type-paramters will be filled in initially based upon other known data, such as the source of the call (if referring to an extension method), and the data-types associated to the non-lambda call parameters. In cases where a match cannot be found this is when you come to the conclusion: "Type parameters cannot be inferred, try defining them explicitly."

I'll try to make the constructors of the lambda expressions as straight forward as possible. The specifics towards the type inference here will require a certain bit of analysis of the statement/expression associated to the lambda expression, based upon the yielded result.

There's a lot of work to be done, this might actually require a later revisit once the statement/expression model is further. I still have to rewrite a large portion of the internal auto-linking system to enable a more realistic view of how it should be done. Especially since the contextual information needed to do some of the inference won't be immediately available.

The other reason for the rewrite of the linking system is with a compiler context provided, I can actually emit error messages/warnings as needed, presently it throws errors, halting the current linker state and generally causing difficulty handling things, especially since I didn't add the appropriate code to handle the errors when they are thrown.

A good example of this is how it relates to the namespace includes (using) of the current context. Since this project is aimed at hobbyist lingual theorists, they'll need something more than a single using reference, so the linking methods will need to provide a compiler context that can give them this contextual information.

A backwards look of the current expression tree might also provide more information that might not be immediately obvious, but this is something I'll investigate as I go further into the type inference. The extra data mostly applies to closures and lifting them into appropriate generated display classes on translation into CIL.

No comments: