id	summary	reporter	owner	description	type	status	priority	resolution	keywords	cc	topic	difficulty	mentor
81	Implement a better type checker for yhc	malcolm.wallace	none	"The implementation of type inference in yhc (also used in nhc98) is occasionally incorrect, always difficult to understand and modify, and entirely undocumented.  As a result, there is no hope of extending it to deal with multi-parameter type classes, functional dependencies, associated types, GADTs, rank-N, or any of the other exciting and widely-used type-system extensions.  The solution - rip it out and replace it completely.  There are a few key requirements:  it must be maintainable, it must be correct, it must give reasonable error messages.  Speed is not a goal.

Ideally, you will also implement one or more of the extensions noted above.  There are opportunities to engage with cutting-edge type techniques like constraint-based resolution, or just to go for plain and simple H-M-style.

= Interested Mentors =
 * Malcolm Wallace <[mailto:malcolm.wallace@cs.york.ac.uk]>

= Interested Students =
 * Charles Blundell <[mailto:blundellc@googlemail.com]>
 * Kenn Knowles <[mailto:kknowles@soe.ucsc.edu]>"	proposed-project	closed	OK	wontfix	types, compilers		YHC	1 person Summer	not-accepted