Re: ReplaceAll in If Statement
- To: mathgroup at smc.vnet.net
- Subject: [mg19506] Re: ReplaceAll in If Statement
- From: "David Bailey" <dave-bailey at freeuk.com>
- Date: Sat, 28 Aug 1999 15:53:24 -0400
- References: <7q20sl$q9i@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Tom Compton wrote in message <7q20sl$q9i at smc.vnet.net>...
>In the following sequence I expected z to evaluate to 1 in the
>Module. It appears that the test in the module does not
>evaluate to either True or False. I don't understand why.
>Can anyone explain?
>
>In[1]:=
>opList={a->True};
>
>In[2]:=
>test[opts___]:=Module[{},
>If[a /. {opts}, z=1, z=2, z=3];
>{a, z} /. {opts}]
>
>In[3]:=
>test[opList]
>Out[3]=
>{{True,3}}
To see what had happened I ran test[opList]//TracePrint. If you do this you
will see that you were in effect calling
test[{a->True}]
However your code is set up to work with
test[a->True]
As a result you end up testing If[{True}, ..... which is indeed neither true
nor false!
David Bailey
Salford Software