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最近我一直在探索Idris中的依賴類型。然而,我克服了一個非常煩人的問題,這是在伊德里斯,我應該用類型簽名開始我的程序。所以問題是,如何在Idris中編寫簡潔的類型簽名?如何在Idris中編寫Vect的正確類型簽名?
例如,
get_member : (store : Vect n String) -> (idx : List (Fin n)) -> (m : Nat ** Vect m (Nat, String))
get_member store idx = Vect.mapMaybe maybe_member (Vect.fromList idx)
where
maybe_member : (x : Fin n) -> Maybe (Nat, String)
-- The below line should be type corrected
-- maybe_member x = Just (Data.Fin.finToNat x, Vect.index x store)
如果我評論的最後一行,編譯將鍵入檢查上述功能, 但如果我做的最後行表達,編譯會報錯。
When checking right hand side of VecSort.get_member, maybe_member with expected type
Maybe (Nat, String)
When checking an application of function Data.Vect.index:
Type mismatch between
Vect n1 String (Type of store)
and
Vect n String (Expected type)
Specifically:
Type mismatch between
n1
and
n
但我這樣做是爲lambda功能,
get_member : (store : Vect n String) -> (idx : List (Fin n)) -> (m : Nat ** Vect m (Nat, String))
get_member store idx = Vect.mapMaybe (\x => Just (Data.Fin.finToNat x, Vect.index x store)) (Vect.fromList idx)
這將是類型檢查爲好。
所以問題是,我應該如何定義類型簽名中正確長度的Vect類型?