template-haskell

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September 2009

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RE: patch applied (ghc): Three improvements to Template Haskell (fixes #3467)
by Simon Peyton-Jones 11 Sep '09

11 Sep '09

| > Declaration-level splices with no "$" | > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | > This change simply allows you to omit the "$(...)" wrapper for | > declaration-level TH splices. An expression all by itself is | > not legal, so we now treat it as a TH splice. Thus you can now | > say | > data T = T1 | T2 | > deriveMyStuff ''T | | Nice. | | There has been talk int the cast about allowing things like | class T, type T | etc in the module export list. Perhaps you should also be able to say | | data T = T1 | T2 | deriveMyStuff (type T) | | rather than using the somewhat odd '' syntax. Interesting idea. You're making use of the *keyword* 'type', although it's unexpected in an expression context. Trouble is, we lack a keyword for 'value'! I suppose we could invent one. Thus module Foo( type T(..), class C, value f, value g ) and deriveMyStuff [type T, value f] I wonder if that would have merit? What do other TH afficionados think? Simon

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How to use Template Haskell build Map ?
by Andy Stewart 08 Sep '09

08 Sep '09

Hi all, I have below instances: instance PageViewState DiredViewState where instance PageViewState StringViewState where I can use Language.Haskell.Exts.Parser scan above instances got list: typeList :: [Type] typeList = [TyCon (UnQual (Ident "DiredViewState")),TyCon (UnQual (Ident "StringViewState"))] So question is how to use Template Haskell and above `typeList` build below `Map` at compile-time? tagmap = M.fromList [(typeIdOf StringViewState, Exists (Dict :: PageViewStateDict StringViewState)) ,(typeIdOf DiredViewState, Exists (Dict :: PageViewStateDict DiredViewState))] Thanks! -- Andy

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