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Re: pattern bugs and comment on intuitive syntax for the

• To: mathgroup at smc.vnet.net
• Subject: [mg115157] Re: pattern bugs and comment on intuitive syntax for the
• From: DrMajorBob <btreat1 at austin.rr.com>
• Date: Mon, 3 Jan 2011 03:54:49 -0500 (EST)

This bothers me:

x /. x + c___ : 0 -> aha[c]
x + y /. x + y + c___ : 0 -> aha[c]

aha[0]

aha[]

I'm accustomed to guessing what works or just trying random things until  
something does... but it gets tiring.

Bobby

On Sun, 02 Jan 2011 03:56:08 -0600, Richard Fateman  
<fateman at cs.berkeley.edu> wrote:

>
>
>   Guess the results.
>
> x+3 /. x+c___ -> aha[c]
> x /. x+c___ -> aha[c]
> x /. x+c___:0 -> aha[c]
>
> compare to
>
> x+y+3 /. x+y+c___ -> aha[c]
> x+y  /. x+y+c___ -> aha[c]
> x+y  /. x+y+c___:0 -> aha[c]
> x+y+a+b  /. x+y+c___ :> aha[c]
> x+y+a+b  /. x+y+c___ :> aha[Plus[c]]
> x+y  /. x+y+c___ :> aha[Plus[c]]
>
>
>
> I think the requirement for the :0 represents a bug. Maybe the
> need for the Plus[], too. The treatment of NullSequences within
> a Flat operator could be different, leaving an operator around.
>
> ............
>
> Another item. really, syntax.
>
> define
>
> GreaterThan[q_]:= #>q&
> gt2=GreaterThan[2]   (* a function of one argument.
>                          is that argument > 2? *)
>
>
> mm[2, 10] /. mm[q_, s_?GreaterThan[q]] :> aha[q, s]
>
>   doesn't give aha..
>
>
> mm[2, 10] /. mm[q_, s_?gt2] :> aha[q, s]
>
> does give aha
>
> this works, though.
> mm[2, 10] /. mm[q_, s_?(GreaterThan[q])] :> aha[q, s]
>
> I love that intuitive syntax. None of that excess
> parentheses and stuff. (sarcasm)
>
> This error would have been
> much more apparent in Lisp.
>
> happy new year.
>
>
>
>


-- 
DrMajorBob at yahoo.com