Curious case of type of 2 in haskell -

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what rationale behind assigning general type num => a 2 instead of defaulting specific type int or integer?

secondly have read @ many places 2 polymorphic value definition of polymorphism doesn't admit constrained variables. 2 polymorphic in haskell?

2 polymorphic can use whatever type of number like. num type class has function frominteger, used here. 2 frominteger (2 :: integer). if 2 not polymorphic have write if wanted non-integer number, because there no automatic coercion in haskell (i.e. can't (1 :: integer) + (1 :: int)). case fractional fromrational way.

polymorphic type variables can have constraints. if not have constraints, called parametric polymorphism , if constrained, bounded parametric or ad-hoc polymorphism. see haskellwiki article on polymorphism.

be aware, should not rely on type inference top-level functions or else may fall trap monomorphism restriction. example if write @ top-level of module:

polymorphic = 42

you may expect polymorphic of type num => a, in reality haskell default type of polymorphic integer.


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