type inference - How does Haskell know which typeclass instance you mean? -


Excellent knowledge about user factor This question arises when you are reading a new chapter in Haskell.

It may be that for example, in the category of Appetitive type, as part of the definition: 

  pure = bus

If I only import control by visiting GHCI , And do: 

  pure (3+)

I do not get anything (understandable) But if I use it in the part of the expression: 

  Pure (3+) & lt; * & Gt; Just 4

I just get 7. I think this is not too surprising, but I am missing a unique story about how types of classes work, I think there is no ambiguity with the call Pure < / Code> here

If my confusion comes to mind, then is there any detail that what is happening?

This is just the type estimate (<<>>) The operator requires both arguments to use the same applicable example, on the right there is a probably , so there may be a on the left So, this figure tells the way in which this example is used here. You can type any expression type in the interpreter by typing : t expression , and perhaps if you go through every subexpression and look at the guessed type, you will get a better picture What is happening.


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