Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!gore!jacob
From: jacob@gore.com (Jacob Gore)
Newsgroups: comp.lang.eiffel
Subject: Re: Passing functions as parameters
Message-ID: <120012@gore.com>
Date: 2 Feb 90 17:04:02 GMT
References: <1832@clyde.concordia.ca>
Reply-To: jacob@gore.com (Jacob Gore)
Organization: Gore Enterprises
Lines: 38

/ comp.lang.eiffel / marcap@hercule.cs.concordia.ca (PAWLOWSKY) / Feb 2, 1990 /
> A while back, the passing of functions as parameters was mentioned.  If
> memory is correct (I don't have a list of comp.lang.eiffel postings, is 
> someone out there keeping a ftp'able copy?) it ended up with someone
> saying it is not needed since you can redefine the function as needed
> in the class.

I take this as confirmation that no, you can't pass functions as parameters
in Eiffel.

Could somebody tell me then what the inheritance-related trick is for
supplying a list class with the following routines:

    1.	apply-routine   -- like LISP's "mapcar": same operation repeatedly
				applied to all elements of the list

    2.	insert-function -- like APL's "/":
				given a list L such that nb_elements(L)>1
				and a fuction F,
					if L.nb_elements > 2 then
						return F(L.first, L.rest)
					else
						return F(L.first, L.second)

The one particularly useful in Eiffel is a combination of 1 and 2:

    3.	for-all		-- given a BOOLEAN function F and a list L,
				return 'true' if F(L.i_th(k)) returns true
				for all 1 <= k <= L.nb_elements

And, of course, a there-exists function is analogous.

Having such features in list classes would make writing assertions about
lists much easier.

Jacob
--
Jacob Gore		Jacob@Gore.Com			boulder!gore!jacob