Lambdas, alphas in Scalaz -

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in many traits' signatures 1 can spot awkwardly looking syntax:

private trait compositionplus[f[_], g[_]] extends plus[λ[α => f[g[α]]]]

could explain me λ[α => f[g[α]]] part? both λ , α seems undefined.

edit: see syntax wonder how interpreted compiler.

this syntax comes kind-projector. compiler plugin rewrites

λ[α => f[g[α]]]

to

({ type l[α] = f[g[α]] })#l




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