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Hello world inspection of haskell data types with template haskell
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| {-# LANGUAGE TemplateHaskell #-} | |
| module Templ1 where | |
| import Language.Haskell.TH | |
| import Templ2 | |
| data Person = P { | |
| name :: String, | |
| age :: Integer | |
| } | |
| thisIsData = $(whatIs ''Person) | |
| thisIsConstr = $(whatIs 'P) | |
| main = putStr $(inspData ''Person) |
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| {-# LANGUAGE TemplateHaskell #-} | |
| module Templ2 where | |
| import Language.Haskell.TH | |
| import Data.List | |
| -- useful sources: | |
| -- https://hackage.haskell.org/package/template-haskell-2.8.0.0/docs/Language-Haskell-TH.html | |
| -- https://hackage.haskell.org/package/data-lens-template-2.1.3/docs/src/Data-Lens-Template.html#makeLenses | |
| whatIs name = do | |
| info <- reify name | |
| case info of | |
| (TyConI dec) -> litE $ StringL "Data Declaration" | |
| (DataConI name typ parentName fixity) -> litE $ StringL "Type Constructor" -- $ show typ | |
| _ -> fail ("Unsupported name: "++nameBase name) | |
| inspData name = do | |
| info <- reify name | |
| inspInfo info | |
| where | |
| inspInfo info = | |
| case info of | |
| (TyConI dec) -> --litE $ StringL (show dec) -- | |
| inspDec dec | |
| _ -> fail ("Unsupported name: "++nameBase name) | |
| inspDec dec = | |
| case dec of | |
| (DataD _ name _ constrs _) -> litE $ StringL $ | |
| (unlines $ map | |
| inspConstr constrs) | |
| _ -> fail $ "Unsupported dec: "++(show dec) | |
| inspConstr con = | |
| case con of | |
| (RecC name varStrictTypes)-> show name ++ " { " ++ (unlines $ intersperse ", " $ map inspVarStrTyp varStrictTypes) ++ " } " | |
| _ -> fail $ "Unsupported record field" | |
| inspVarStrTyp (v,_,t) = (nameBase v) ++ " :: " ++ show t | |
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