对 Haskell 数字类型感到困惑

Question

I'm trying to create a foldr example that converts an Integral to a list of digits (ie, [Int] ).

pickDigit num pos = (num `div` (10^pos)) `mod` 10

toDigits num = foldr (\pos acc -> (pickDigit num pos):acc) [] [0 .. floor (logBase 10 num)]

This loads successfully. But when I try to run it, for example

> toDigits 1234

I get a type error message I don't understand.

When I ask Haskell for the types of the loaded code and explicitly include those types in the source file, I get error messages on loading. When I try to explicitly restrict the types to Integer or Int , I get more error messages.

I'd appreciate some suggestions. Thanks.

Answer 1

logBase requires Floating, but it's not

This works:

[0 .. floor (logBase 10 $ fromIntegral num)]