** Summary **

[Richard Suchenwirth] 2002-11-15:  I still remember how [Cameron Laird] groaned
when I showed how to simulate [array]s of function pointers ([Tcl]'s
equivalent being the names of functions, [everything is a string]). After
re-reading man Tcl last night (always recommended, even after years in the
business ;-), it dawned on me this morning that we don't have to simulate that
- using Tcl's substitution rules, we just have it.


** Description **

Consider:

======
#--------------------------------- dummy procs as playing material
proc eat    x {puts "eating $x"}
proc drink  x {puts "drinking $x"}
proc inhale x {puts "inhaling $x"}

#---------------------------------- building the mapping table
array set fp {solid eat liquid drink gaseous inhale}

#---------------------------------- testing:
foreach {state matter} {solid bread  liquid wine  gaseous perfume} {
    $fp($state) $matter
}
#------------------- results in:
eating bread
drinking wine
inhaling perfume
======

What happens to `$fp($state)`? First `$state` is substituted, as is the rule
with arrays. Then the array element e.g. `$fp(solid)` is looked up in the
array, and its result makes the command name ''eat'', which finally is executed
with the argument e.g. ''bread''.

----

[KPV] 2002-11-15:  funny, I use an array of function pointers in the [Møiré
Patterns] program I posted here just yesterday. I needed to draw the foreground
or background as one of several patterns and I wanted an easy way to make this
extensible. So I just created an array of function pointers, and now to add a
new type is just write the subroutine and add its name and ''reference'' to the
array. Furthermore, in the [GUI] [widget] where the user can select the type, I
just use `[[array names fptr]]` to get the list. Below is the relevant code
snippets:

======
array set fptr {"Parallel Lines" Parallel "Radial Lines" Radial \
    Circles Circles}

proc Show {who angle} {
    global fptr SS
    $fptr($SS($who,type)) $who $angle
}
======

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