Opened 3 years ago

Last modified 3 months ago

#8207 new feature request

Pretty Printer for textual version of Language (name) in DynFlags

Reported by: Fuuzetsu Owned by:
Priority: low Milestone:
Component: GHC API Version: 7.7
Keywords: newcomer Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


I feel that the GHC API could benefit from a Show instance for Language in DynFlags.hs.

Currently, if we want to display the language being used we have to do something like

          foo inf = case hmi_language inf of
            Nothing -> Nothing
            Just Haskell98 -> Just "Haskell98"
            Just Haskell2010 -> Just "Haskell2010"

This is pretty much just the Show instance (over Maybe) and Haskell can derive it for us automatically: we just need to change deriving Enum to deriving (Enum, Show). The above solution is not the most robust ever as if this data type is ever changed, this starts to form an incomplete pattern. If we have a catch all _, GHC complains about overlapping patterns. Easily solved with show <$> hmi_language inf.

Change History (3)

comment:1 Changed 3 years ago by carter

  • Summary changed from Show instance for Language in DynFlags to Pretty Printer for textual version of Language (name) in DynFlags

to further clarify, based upon further discussion on IRC,

[23:39:41] <Fuuzetsu>	 Yep, all I want is Language -> String out of 
only having DynFlags which provides Maybe Language.

Its worth noting that this probably shouldn't be a show instance, because Language Standards need not have only the form (capital letter)(aphanumeric*).

The key point is a function to pretty print the name of the Language should be exposed. And probably more future proof to funny names if its not done via Show specifically.


renderLanguageName :: Language -> String 

or the like

comment:2 Changed 3 years ago by simonpj

OK with me; maybe send patch?


comment:3 Changed 3 months ago by thomie

  • Keywords newcomer added
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