[Haskell-cafe] How to unify these three types with identical structures into one definition?

[MigMit]

You probably mean

newtype Expr = Expr (ExprG Expr)

Az iPademről küldve

2018. dec. 14. dátummal, 14:08 időpontban Tobias Brandt <to_br at uni-bremen.de> írta:

> Hello, 
> 
> my adhoc solution would be to add a type parameter:
> 
> data ExprG a = Var String
>   | Enclosed String a String
>   | Prefix a a 
>   | Ternary a String a String a deriving Show
> 
> 
> type Expr = ExprG (ExprG ())
> 
> type ExprL = ExprG [Expr]
> 
> 
> Cheers,
> 
> Tobias
> 
> 
> 
>> On 12/14/18 1:56 PM, ducis wrote:
>> Hello,
>> 
>> Say I have a certain type for parse trees:
>> data Expr = Var String
>>    | Enclosed String Expr String
>>    | Prefix Expr Expr
>>    | Ternary Expr String Expr String Expr
>>    deriving (Show,Eq,Ord,Generic)--,Typeable)
>> 
>> Then I want a new type where every occurence of "Expr" definition changed to "[Expr]":
>> data ExprL = VarL String
>>    | EnclosedL String [Expr] String
>>    | PrefixL [Expr] [Expr]
>>    | TernaryL [Expr] String [Expr] String [Expr]
>>    deriving (Show,Eq,Ord,Generic)
>> 
>> Sometimes, I also want to use a DList instead of list.
>> data ExprD = VarD String
>>    | EnclosedD String (DList Expr) String
>>    | PrefixD (DList Expr) (DList Expr)
>>    | TernaryD (DList Expr) String (DList Expr) String (DList Expr)
>>    deriving (Show,Eq,Ord,Generic)
>> 
>> They have exactly the same structure, is there a way to unify the three definitions into one?
>> Furthurmore, is it possible to generalise the latter two for all Functors ?
>> 
>> Thanks,
>> ducis
>> 
>> 
>> _______________________________________________
>> Haskell-Cafe mailing list
>> To (un)subscribe, modify options or view archives go to:
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
>> Only members subscribed via the mailman list are allowed to post.
> _______________________________________________
> Haskell-Cafe mailing list
> To (un)subscribe, modify options or view archives go to:
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe
> Only members subscribed via the mailman list are allowed to post.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20181214/b9f775ee/attachment.html>