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Petr
Petr

Reputation: 63349

Is it possible to generate comments to functions in Template Haskell?

In our project we have a lot of TH-generated functions. It'd make sense to add generic comments to them so that they are visible in Haddock/Hoogle. At the very least, something like "This has been generated by TH." Is something like that possible?

Upvotes: 53

Views: 621

Answers (2)

141592653
141592653

Reputation: 723

Yes it is.

Here is a basic example that declares a copy of some function, adds hello_ in front of its name, and adds Hello ! in front of its documentation.

{-# LANGUAGE TemplateHaskell #-}

module MyTH where

import Language.Haskell.TH
import Language.Haskell.TH.Syntax

helloCopy :: Name -> Q [Dec]
helloCopy name = do
  doc  <- getDoc (DeclDoc name)
  let helloName = mkName ("hello_" ++ nameBase name)
  let helloDoc = case doc of
        Nothing -> "Hello !"
        Just old -> "Hello !" ++ old
  addModFinalizer $ putDoc (DeclDoc helloName) helloDoc
  [d| $(varP helloName)= $(varE name) |]

module MyModule where

import MyTH

-- | Interesting stuff about blub
blub :: Int
blub = 4

$(helloCopy 'blub)

Now if you run haddock you will get a documentation for hello_blub that says "Hello ! Interesting stuff about blub"

Upvotes: 3

glguy
glguy

Reputation: 1090

This would be nice to have but it isn't currently possible in GHC.

Upvotes: 2

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