Rule form

Some functions are available in ''rule form''.

These rule form functions are functions that create a new [[type:function]].
That new function, the rule, applies some transformation to the input and returns the result.

A rule is like a normal function with all parameters given, except for the @input@.

Rules are often combined using the + operator, for example:
> # First all "a"s are replaced, then all "b"s.
> remove_as_and_bs := replace_rule(match: "a", replace: "") +
>                     replace_rule(match: "b", replace: "")
> 
> text_with_as_and_bs := "bla bla bla"
> text_without_as_and_bs := remove_as_and_bs(text_with_as_and_bs)

