Arabbit.427
net.lang.apl
utzoo!decvax!duke!harpo!ihnss!houxi!npois!alice!rabbit!ark
Thu Apr  8 10:50:17 1982
Re: apl parsing
I meant the hardest part of MACHINE parsing, because your typical
parser changes the characters to tokens left to right and then
parses during execution right to left.  When parsing right to left
and you've seen ...]-X, you do indeed have to find the matching
[ and look beyond it before you can figure out what to do about the -.

You might argue "But you can classify the - as monadic or dyadic
on the left to right scan".  Indeed you might!  But you can't in
such simple cases as A-B, because you don't know until you get
there whether A is a variable or a monadic function.

It was a long time before IBM APL knew how to handle +/[X]-Y