gistfile1.txt

Implement `choose`, a conditional combinator which will execute one of
two functions, depending on the state of a flag. We take advantage of
a little hack here. Store the pointers into a jump table with two
fields, and use the flag as the index. Default to the *false* entry,
since a *true* flag is -1.

~~~
: choice:true
d 0

: choice:false
d 0

: choose
i listlist
r choice:false
r choice:true
i liadfeca
r choice:false
i re......
~~~