Hello all, When I edit Haskell code in a text editor, I often want to point at an expression and be told its type. (Even assuming that this feature only works when the entire file type-checks correctly, it would still be very useful to me.) For example, in let c:cs = "string" in ... I would like to point at "c" and be told that c :: Char c:cs :: [Char] I divide this functionality into two parts: 1. Given a Haskell program, produce a list of pairs (span, type), where "span" is a contiguous region in the source code that parses as an expression, and "type" is the type of the expression (possibly universally quantified and/or with context). 2. Make this information easy to generate and view in an editor. Focusing on part 1, I see two possible approaches: A. Ask an existing Haskell interpreter/compiler to output the information. I looked briefly at the implementations listed at http://www.haskell.org; none of them seems to produce anything (i.e., any debugging output) from which the necessary information can be extracted. Therefore, to take this approach, we would need to modify an implementation. I would be very happy to be corrected on this observation. B. Connect a Haskell parser (e.g., hsparser) to a Haskell type checker (e.g., _Typing Haskell in Haskell_). This is the preferred approach because the solution would not depend on the internals of any Haskell implementation. However, the output of hsparser is neither typed nor desugared for piping into _Typing Haskell in Haskell_, so some conversion/desugaring work is required. I would appreciate any comments, pointers to existing work, or other help on this project. In particular, how much work would be involved in approach B above, and has it already been done? Thanks in advance! -- Edit this signature at http://rodimus.digitas.harvard.edu/cgi-bin/ken/sig Dumpster Clocking: The tendency when looking at objects to guesstimate the amount of time they will take to eventually decompose: "Ski boots are the worst. Solid plastic. They'll be around till the sun goes supernova."