[wk_end]

It reads as a little ambiguous to me in your comment, so just to be clear:

A polymorphic type - "a type wrapping another type" - isn't the same thing as a higher-kinded types.

Higher-kinded types are what let you express, in the language, the very notion of "a type wrapping another type". A "List Int" is a type wrapping another type; a "Maybe Int" is another type wrapping another type; but we can also say that "List Int" and "Maybe Int" (and etc.) can be abstracted over as "Monad Int"s. Monad is a higher-kinded type because it's a type wrapping types wrapping another type.

[jpc0]

You missed the point though with that. It's explicitly not a monad if it doesn't have an equivalent of bind. If I need to write an imperative function to process the monad into another it's not a monad.

If however I have a List<byte> and would like it to become Maybe<UInt128>. A loop is always a jmp of some sort, a bind though could become a SIMD operation or be passed off to a coprocessor and I as the programmer would be none the wiser since all I cared about was the end result.