[Haskell Cafe] Data construction: how to avoid boilerplate code?
Hi haskellers, I have a datatype of this sort: data Type = Status | Message | Warning | Error | StepIn | StepOut deriving (Eq, Show) and (at this moment) two fabric-like functions: makeType :: String -> Type makeType c = case c of "-$-" -> Status "-M-" -> Message "-W-" -> Warning "-E-" -> Error "->>" -> StepIn "<<-" -> StepOut otherwise -> error "Uknown Message Type" deduceType :: Integer -> Type deduceType n = case n of 240 -> Status 64 -> Message 32 -> Warning 8 -> StepOut 4 -> StepIn 2 -> Error otherwise -> error "Unknown Message Type" how can I avoid boilerplate code at this stage? The thing that I really need is some n-type constructor, kind of a fabric for a variety of types with the possibility to add them on the fly (I have simple Integer and String here, but they could be much more sophisticated). I don't need the possibility to unpack the original value (e.g. "-$-" or 240) once the Type is created - in this case I can always have some sort of mapping to deduce it at any moment, so it will be redundant to carry it through the code explicitly The example is rather short and simple, but I have some more places in code, where the same problem is observed. Is there any generic solution? Thanks in advance -- Regards, Paul Sujkov
On Wed, Jul 29, 2009 at 6:27 AM, Paul Sujkov
Hi haskellers,
I have a datatype of this sort:
data Type = Status | Message | Warning | Error | StepIn | StepOut deriving (Eq, Show)
and (at this moment) two fabric-like functions:
makeType :: String -> Type makeType c = case c of "-$-" -> Status "-M-" -> Message "-W-" -> Warning "-E-" -> Error "->>" -> StepIn "<<-" -> StepOut otherwise -> error "Uknown Message Type"
deduceType :: Integer -> Type deduceType n = case n of 240 -> Status 64 -> Message 32 -> Warning 8 -> StepOut 4 -> StepIn 2 -> Error otherwise -> error "Unknown Message Type"
how can I avoid boilerplate code at this stage? The thing that I really need is some n-type constructor, kind of a fabric for a variety of types with the possibility to add them on the fly (I have simple Integer and String here, but they could be much more sophisticated). I don't need the possibility to unpack the original value (e.g. "-$-" or 240) once the Type is created - in this case I can always have some sort of mapping to deduce it at any moment, so it will be redundant to carry it through the code explicitly
I am not sure what you're asking. Are you saying that what you have written is boilerplate? What code are you writing that could be automatically deduced with enough smartness? Give an example of what you might like the solution to look like. Luke
The example is rather short and simple, but I have some more places in code, where the same problem is observed. Is there any generic solution? Thanks in advance
-- Regards, Paul Sujkov
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Paul Sujkov