In Haizhu, in 2010, 17.31% of the total population lived in this ZIP code.
In this area, there are 1,735 households, with a population of 4,414 and an average living room size of 676 m². The percentage of people living in this district, in the villages and towns included in the area, is made up of 1.73% in Guanxin, 2.14% in Wangshan, 2.09% in Lianji, 2.08% in Huayuan, 0.99% in Renceng, 0.94% in Xiacheng, 0.75% in Panlong and 0.68% in Renmin.
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Category:Township-level divisions of GuangdongQ:
Haskell Bifunctor function errors out
I have a function that attempts to use the function in GHCi:
testBifunctor :: Bifunctor b => (b, b) -> b
testBifunctor ((b,b), (c,d)) = maybe (return (b,b)) (return (c,d)) b
I get the following error:
Couldn't match expected type `b' with actual type `(b, b)'
`b' is a rigid type variable bound by
the type signature for testBifunctor :: Bifunctor b => (b, b) -> b
at./src/Main.hs:29:14-37
Relevant bindings include
it :: b (bound at./src/Main.hs:29:3)
In the first argument of `maybe', namely `(return (b,b))'
In the expression: maybe (return (b,b)) (return (c,d)) b
I am not sure why it is a rigid type variable as it is defined as a function, not a data type. Also, I am unsure how to deal with that error. I have attempted many solutions but have been unsuccessful.
A:
You can use the GHCi builtin by adding the import Prelude to your file, and then use functions like maybe like this:
testBifunctor
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