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Can an analog of the S combinator be expressed in Haskell using only standard functions (without defining it by equation) and without using lambda (anonymous function)? I expect it to by of type (a -> b -> c) -> (a -> b) -> a -> c.
For example, an analog of the K combinator is just const.
In fact i am trying to express the function \f x -> f x x using standard functions, but cannot think of any standard non-linear function to start with (that is a function that uses its argument more than once).
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Haskell. Copy. But informally… a combinator is something that combines other things. And it is in that informal sense that we use it here! In our context, parser combinators are functions on parsers: functions that combine and transform parsers into other parsers, to handle such things as backtracking, or repetition.
A combinator is a higher-order function that uses only function application and earlier defined combinators to define a result from its arguments.
s = (<*>) for the ((->) r) Applicative instance.
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Although it doesn't look like it at first, ap is the S combinator (and join is the combinator you're really after).
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