Options, OptionsPattern, and OptionsValues
- To: mathgroup at smc.vnet.net
- Subject: [mg118851] Options, OptionsPattern, and OptionsValues
- From: blamm64 <blamm64 at charter.net>
- Date: Fri, 13 May 2011 06:26:36 -0400 (EDT)
Hi,
I am developing a package for implementing polynomial linear least
squares time domain filter and ran across the subject of this post as
an interesting alternative to what I was doing to pass options. There
is one exported function, so it gets all the user-supplied options,
and it then handles which private functions actually do the work and
how they go about by receiving options from the exported function. So
I tried what amounts to the following:
In[1]:= Options[f]={a->"None",b->"both",c->"either",dog->False};
In[2]:= f[x_,OptionsPattern[]]:=If[OptionValue[dog],g[x],h[x]]
In[3]:= g[x_,OptionsPattern[f]]:={3 x,OptionValue[a],OptionValue[b]}
In[4]:= h[x_,OptionsPattern[f]]:={4*x/7,OptionValue[a],OptionValue[c]}
In[5]:= f[2,c->"left"]
Out[5]= {8/7,None,either}
In[6]:= f[2,c->"None"]//Trace
Out[6]= {{c->None,c->None},f[2,c->None],If[OptionValue[f,{c-
>None},dog],g[2],h[2]],{OptionValue[f,{c-
>None},dog],False},If[False,g[2],h[2]],h[2],{(4 2)/7,OptionValue[f,
{},a],OptionValue[f,{},c]},{{{1/7,1/7},2/7,2/7},(4 2)/7,8/7},
{OptionValue[f,{},a],None},{OptionValue[f,{},c],either},
{8/7,None,either}}
My hope was to pass options to the exported function, which used some
of those options to determine which worker to call and then passed all
those options to the workers, who decide what options they need and
what to do with those options. I was trying to implement 'find what
varies and encapsulate it'. I came up with this scheme by looking at
Documentation and reading what I could find in this forum, but saw
nothing in either place (perhaps because it is 'intuitively obvious'
to some this cannot be done ... ). If this had worked, it would have
scaled with increasing option number beautifully. I ended up using
alternative of passing only what the workers needed in the calls to
them in the main exported function using OptionValue in the main and
using a pattern <opts___> in the workers, but that does not scale well
at all with increasing number of options.
So I think all I can hope to do is have someone please explain to me
the Trace, which I still have a hard time decoding. I got stuck on
the very first 'list'. But it is plain to see where the option 'got
lost'. What is not plain to me is why. I'm probably missing some
very fundamental Mathematica evaluation paradigm.
Thanks to any and all who help me out.
-Brian L.