_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