how to make the function "length" from "map" and "sum"

[John Mann]

   Hello, I am working my way through Simon Thompson's
Haskell book, and one exercise has me baffled. That is
"how would you define the "length" function using
"map" and "sum" "? Any help on this would be
appreciated. 
John Mann

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"I'd rather be debugging...." - Anon

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