haskell - All Same Lengths Function -



haskell - All Same Lengths Function -

i'm trying write function [a] -> bool returns true when elements of list have same lengths.

i tried using list recursion , extracted first 2 elements of list x : y : xs compared length of x , y length x == length y case determination. however, ghci complains types of x , y:

couldn't match expected type `a' actual type `[a0]' `a' stiff type variable bound type signature [a] -> bool in first argument of `length', namely `x' in first argument of `(==)', namely `length x' in expression: length x == length y

why happening , how prepare it? clearly, length :: [a] -> int == length :: [a] -> int returns bool correct. in fact, replacing look true compiles.

we can simply, actually.

samelengths :: [[a]] -> bool samelengths [] = true samelengths (x:xs) = (\y -> length y == length x) xs

no need recursion - of lengths same iff equal first one, extract first , utilize all check rest.

as why can't define [a], remember [string] [[a]] [a]. need [[a]] because length must defined whatever a in [a].

haskell

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