parsley-garnish- A collection of GHC plugins to work with parsley
MaintainerJamie Willis
Safe HaskellNone



This plugin hijacks the regular Haskell syntax for Untyped Template Haskell (UTH). Since parsley uses Typed Template Haskell (TTH), it is unlikely that a user of the library will need to be using UTH in the same file (with the possible exception of top-level splices, or quotes other than the basic [|x|]). This plugin will transform every UTH quote in a file so that it represents a value of Quapplicative q => q a. This transformation is as follows:

qsucc :: Quapplicative q => q Int -> q Int
qsucc qx = [|$(qx) + 1|]
-- goes to:
qsucc qx = makeQ (_val qx + 1) [||$$(_code qx) + 1||]

Values of Defunc can also be spliced in directly:

diffcons :: Defunc a -> Defunc ([a] -> [a]) -> Defunc ([a] -> [a])
diffcons qx qdxs = [| $(COMPOSE) ($(CONS) $(qx)) $(qdxs) |]

And lambda abstraction works too (along with any other syntax):

diffcons' :: Defunc (a -> ([a] -> [a]) -> [a] -> [a])
diffcons' = [|\x dxs -> $(diffcons [|x|] [|dxs|])|]

The disadvantage to this plugin currently is that it does not make any attempt to leverage the specialised parts of Defunc to improve the code generation and inspectibility. The user would be left to use this manually.



plugin :: Plugin Source #

This plugin repurposes Untyped Template Haskell quotes (and splices within them) to be Quapplicative values.