character redefinition environment

[Enzo Cordes <plink@veribox.net>]

Hi list,

I want to assign Metapost graphics to single letters (in a newly defined 
evironment, that take care of these assignments). The purpose is being 
able to rapidly build huge tables containing lots of these symbols.

Everything works fine if I assign these graphics to non-letters, e.g. 
"|", but somehow it doesn't work with normal letters.

Here is what I tried (with a simple Foo instead of Metapost graphics):

\definesymbol[foosymbol][{\tt Foo}]
\def\startmychars{%
\bgroup\catcode`\|=\active\def|{\symbol[foosymbol]}}
\def\stopmychars{\egroup}

This works with | as reassigned character without any problems. But, we 
want to have normal characters in the table, no punctuation marks, etc. 
Does anyone know what to do to reassign a special definition for a 
letter e.g. like uppercase B or else?

I got this error:
(/usr/local/share/texmf/tex/context/base/pdfr-ec.tex)
! Undefined control sequence.
\startmychars ...up \catcode `\B=\active \defB
                                                   {\symbol[foosymbol]}
l.24 \startmychars

which seems to indicate that B is not recognized as active character in 
the "\defB"?


Any hints very welcome,
Enzo.