Why do 3 and x (which was assigned 3) have different inferred types in Haskell? [duplicate]

This question already has an answer here: 开发者_Go百科What is the monomorphism restriction? (1 answer)

Why are polymorphic values not inferred in Haskell?

Numeric literals have a polymorphic type: *Main> :t 3 3 :: (Num t) => t But if I bind a variable to such a literal, the polymorphism is lost:

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