:load test/poly-instantiate/poly-instantiate.disco
:type foldr
:type foldr (\x, y. x)
:type foldr (\x, y. y)
:type foldr (\x, y. x+1)
:type foldr (\x, y. y+1)
:type foldr (\x, y. y+1) 1
:type foldr (\x, y. y+1) (-1)
:type foldr (\x, y. x) false
:type foldr (\x, y. x+1) (1/2)
:type foldr (\x, y. x-1) (1/2)