[Haskell-beginners] definition of combinator

[Jan Jakubuv]

Hi Michael,

On Sun, Aug 23, 2009 at 05:44:27PM -0700, Michael Mossey wrote:
> "A combinator is a higher-order function that uses only function
> application and earlier defined combinators to define a result from its
> arguments."
> 
> Okay, so I believe a "higher-order function" is a function that takes 
> function(s) as its argument(s). I don't know what "uses only function 
> application" means. Application of what functions to what? 

Briefly, a combinator applies “earlier defined combinators” to “its
arguments”. But remember that a combinator's argument can be a function as
well, so it may become more complicated. Then it simply applies functions
(other combinators, combinator's arguments, library functions) to their
arguments (other combinators, combinator's arguments, library functions,
constants, ...).

Finally, I guess that the word “only” suggests that it doesn't read any
parsed text by itself but it only calls (combine) other parsers.

Sincerely,
    Jan.



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