2 Jul
2021
2 Jul
'21
6:40 a.m.
<resending with the program as an attachment, as 100K is considered big
here, and no images hidden in reply. moderator, you can kill the prior
messages. computers are hard.>
To show you what I mean, here is a parser I wrote recently for a simple Go
expression evaluator, in Go. It has all Go's precedence levels and
operators. The one odd detail is that >= etc. can be combined, as in 1 >= 2
3, but that doesn't matter in the context of this
program and is easily
avoided with a few more lines in cmpList.
I'm using a screen grab because GMail refuses to leave my indentation
alone. I left factor off. It's got all the usual details but it's the leaf
of the grammar and of no interest here.
Note that this could easily have been made a table instead of a bunch of
one-line functions.
Parsers are easy to write. It took us a generation (or more) to understand
that, but it's remarkable nonetheless. The first big step might have been
realizing that recursion was a good idea, even if you weren't writing LISP,
if the data structure is itself recursive.
-rob