Infix expressions

[Hal Daume III]

> Is there any reason other than potential confusion when one of the two
> backquotes is accidentally omitted?

I thought about this a while ago and I think it probably simply has to do
with complexity of expressions.  If you allow arbitrary expressions to
appear within the ticks, you have a problem with:

  x `f a `b` g c` y

does this mean

  (b (f a) (g c)) x y

or

  f a x (g c b y)

or what?

You could impose the constraint that you can't have embedded ticks, but
this would grossify the CFG.  Furthermore, you then have the case of, why
isn't this valid:

  a `f (x `g` y)` b

where the embedding is unambiguous because of the parentheses.  i don't
really know, but i find this fairly difficult to read.

  a `h` b where h = x `g` y

is a lot simpler imo...

 - Hal