You probably mean
newtype Expr = Expr (ExprG Expr)
Az iPademről küldve
2018. dec. 14. dátummal, 14:08 időpontban Tobias Brandt
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
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