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Re: Pattern evaluation depending on order of definitions

• To: mathgroup at smc.vnet.net
• Subject: [mg74626] Re: Pattern evaluation depending on order of definitions
• From: dh <dh at metrohm.ch>
• Date: Thu, 29 Mar 2007 02:26:28 -0500 (EST)
• References: <eud36i$kp4$1@smc.vnet.net>

Hi Hannes,

Mathematica stores UpValues according to the creterion of increasing

generality. 

More specific rules are stored first. Convince yourself by: ??hh and 

??gg. During evaluation, Mathematica uses the first matching rule it finds.

Now Mathematica has obvioulsy difficulties to determine that _h[1] is more 

specific than _h[n_Integer] as you can see by ??h. I consider this a bug 

and Wolfram should take not.

What you can do is to make your definition in the correct order.

Daniel



Hannes Kessler wrote:

> Hello Mathematica experts,

> 

> please consider the following 2 examples:

> 

> _g[1] := -1;

> _g[n_Integer] := 1;

> g["something"][1]

> --> -1

> 

> _h[n_Integer] := 1;

> _h[1] := -1;

> h["something"][1]

> --> 1

> 

> The first example is what I want: Objects with head g applied to 1

> should return -1 and applied to other integers should return +1. The

> only difference in the second example is the order of the definitions.

> It appears that Mathematica does not check for further definitions

> matching h["something"][1] more accurate.

> 

> This is different in the following two examples:

> 

> gg[1] := -1;

> gg[n_Integer] := 1;

> gg[1]

> --> -1

> 

> hh[n_Integer] := 1;

> hh[1] := -1;

> hh[1]

> --> -1

> 

> Here, the order of the definitions has no influence. Mathematica

> checks all definitions and chooses the best matching one. What is the

> reason for this different behaviour?

> 

> Thanks in advance,

> Hannes Kessler

> 

>