# infix.ss: infix expressions for PLT Scheme

_infix.ss_: _infix_ expressions for PLT Scheme
Danny Yoo (dyoo@hkn.eecs.berkeley.edu / dyoo@wpi.edu)
Quick Example
-------------
> (require (planet "infix.ss" ("dyoo" "infix.plt" 1 0)))
> (infix 3 * 5 + 4 * 6 + ((7 + 8) * 9))
174
> (define (sq x) (* x x))
> (infix sqrt(sq(3) + sq(4)))
5
> (define (in-half-open? x a b)
(infix a <= x < b))
> (in-half-open? 3 1 10)
#t
> (in-half-open? 3 1 2)
#f
This pretty much covers what infix does.
Syntax
------
(infix ...)
which expands whatever is in '...' into equivalent Scheme syntax.
Expression types handled by infix
---------------------------------
* Arithmetic expressions involving +, -, *, /, all with standard
precedences.
* Superfluously parenthesised expressions. (((((a))))) ==> a
* Procedure calls in the unholy style.
f(x, y, ...) ==> (f x y ...)
(Yes, I'm abusing UNQUOTE.)
* Chained comparisons. (<, <=, =, >, >=)
Left to right, with quick escape if any comparison fails.
(infix a <= b < c)
expands to the equivalent code:
(let ([tmp b])
(if (<= a tmp)
(if (< tmp c)
#t
#f)
#f))
Caveats
-------
I try to maintain lexical scope, so if the arithmetic or comparison operators
are rebound, infix doesn't works on them. I might make another release to
give infix a more programmable syntax, but I don't want to take this joke that far yet.
Bugs
----
Syntax location information isn't as preserved as it should be. I need
another macrology lesson to make sure I understand how to do this.
Thanks (and apologies)
------
Thanks to Guillaume Marceau, Dan Dougherty, Kathi Fisler, and everyone
involved with PLT. I hope people can forgive me this joke.
References
----------
mzscheme reference manual: http://download.plt-scheme.org/doc/360/html/mzscheme/
parser-tools: http://ja.soegaard.net/planet/html/collects/parser-tools/doc.txt
chained comparisons/python reference manual: http://docs.python.org/ref/comparisons.html