Re: Patterns and default arguments
- To: mathgroup at smc.vnet.net
- Subject: [mg28137] Re: Patterns and default arguments
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Sun, 1 Apr 2001 00:08:01 -0500 (EST)
- References: <9a438f$cs9@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Jeff:
How about the following?
f[x1_,x2:(y_/;MatchQ[y,{___Integer}]):{}]:={x1,x2}
f[3]
{3,{}}
f[3,2]
f[3,2]
f[3,{1.2}]
f[3,{1.2}]
f[3,{1,2}]
{3,{1,2}}
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565
"Jeff DuMonthier" <jeff at lheapop.gsfc.nasa.gov> wrote in message
news:9a438f$cs9 at smc.vnet.net...
> I am trying to combine a pattern with a default argument in a delayed
> set expression and it is not working.
>
> I can make a default argument work like this: f[x1_, x2_List:{}]:=...
>
> And the pattern works like this: f[x1_, x2:{_Integer...}]:=
>
> But if I combine the two like this: f[x1_, x2:{_Integer...}:{}]:=
> Mathematica accepts it without error and the pattern expression works
> but the default does not.
>
> Am I using the wrong syntax or can the two just not be combined?
>
>
> Also, is there a way to specify a pattern for aguments to something
> defined as a function (i.e. 'Function[...]') rather than a delayed set?
> I have to use 'Function' or ()& in order for the head to be 'Function'
> rather than 'Symbol'.
>
> -Jeff DuMonthier
>