Ambiguous Types Using ListLike

Question

I am writing a function in Haskell to make a histogram from any element ListLikewith Ord:

import qualified Data.ListLike as LL
...
frequencies :: (Ord x, LL.ListLike xs x) => xs -> [(x, Int)]
frequencies xs = LL.map (\x->(LL.head x, LL.length x)) $ LL.group $ LL.sort xs

When I try to compile the above code, I get an error of ambiguous types:

 Ambiguous type variable `full0' in the constraint:
 (LL.ListLike full0 xs) arising from a use of `LL.group'
 Probable fix: add a type signature that fixes these type variable(s)
 In the expression: LL.group
 In the second argument of `($)', namely `LL.group $ LL.sort xs'
 In the expression:
 LL.map (\ x -> (LL.head x, LL.length x)) $ LL.group $ LL.sort xs

LL.grouphas a type (ListLike full0 full, ListLike full item, Eq item) => full -> full0that matches (Eq a) => [a]->[[a]]speaking in terms of regular lists.

I do not understand why there is a problem with ambiguous types. Is Haskell somehow unable to conclude that there is a type such as "ListLike with fullas elements", i.e. full0?

Answer 1

Haskell - , , "ListLike full ", .. full0?

, , full0, Haskell , . : , full0, full : [full] Data.Sequence.Seq full . - LL.map, full0 [full] frequencies.

full0 [full], - LL.map frequencies map .