haskell - Polymorphic self application -


i have example of system f plymorphism don't understand: enter image description here

if remove types remain: \f.\a.f (f a) makes no sense.

can me this? thank you!

the erased term make sense: in haskell \f -> f (f a), ordinary function applies first argument second, , again result.

the difference between \f -> <body> , \f.\a. <body> 1 of notation. if prefer, write haskell term \f -> \a -> f (f a), equivalent syntactically bit closer erased system f.

(note double not self application, \f -> f f.)


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