[m-dev.] For review: add '..'/2 and series/3 to list.m

[Ralph Becket]

>From Fergus Henderson on 26/09/2000 19:22:51
> > 
> > library/list.m:
> > 	Added '..'/2 - generates lists of ascending integers.
> > 	Added list__series/3 - higher order function used to
> > 		generate various kinds of series.
> 
> The new functions should be mentioned in the NEWS file.

Done.

> > +	% list__series(X, OK, Succ) = [X0, X1, ..., Xn]
> > +	% 	where Xk = Succ^k(X) and OK(Xk) and not OK(Succ^(n+1)(X)).
> > +	%
> > +:- func list__series(T, pred(T), func(T) = T) = list(T).
> > +:- mode list__series(in, pred(in) is semidet, func(in) = out is det) =
out
> > +		is det.
> 
> I think the documentation there is rather cryptic.
> It uses a lot of semi-formal notation which is not defined anywhere.
> It's not as understandable as an informal definition,
> and not as well-defined or precise as a genuinely formal definition.

How about this...

list__series(X, OK, Succ) = [X0, X1, ..., Xn]
where X0 = X and successive elements Xj, Xk
a computed as Xk = Succ(Xj).  The series
terminates as soon as an element Xi is
generated s.t. not OK(Xi); Xi is not included
in the output.

> > +	% Lo `..` Hi = [Lo, Lo + 1, ..., Hi]
> > +	%
> > +:- func int `..` int = list(int).
> 
> Here you should document what happens when Hi < Lo.

How about...

Lo `..` Hi = [Lo, Lo + 1, ..., Hi] if Lo =< Hi
           = [] otherwise

--
Ralph Becket      |      MSR Cambridge      |      rbeck at microsoft.com 

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