Q - Equational Programming Language

[Massimo Dentico]

Excerpt from “Q - Equational Programming Language” home page
- http://www.musikwissenschaft.uni-mainz.de/~ag/q/

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[...]

Using  Q is supposed to be fairly simple: you throw together  some
equations,  start the interpreter and then type in the expressions
you  wish to evaluate. All this can be done with a few keystrokes,
if  you use the GNU emacs Q mode supplied with the package, or the
Qpad GUI frontend under Windows95/98/NT (see screenshot).

[...]

In  difference to other functional languages, Q is entirely  based
on  the  notions  of  rewrite  rules, reductions  and  irreducible
expressions  (also known as normal forms) pertaining to  the  term
rewriting  calculus. A Q "program," called a script, is  simply  a
collection of equations which are treated as rewrite rules and are
used  to reduce expressions to normal form. The normal form of  an
expression  denotes its value. Q has no rigid distinction  between
"constructor"  and "defined" function symbols and it  also  allows
you  to evaluate expressions containing variables. Basically, both
sides  of an equation may involve arbitrary expressions. Therefore
Q can also be used as a tool for symbolic expression evaluation.

The  implementation  is based on an efficient  left-to-right  tree
pattern  matching algorithm and an abstract stack machine for  the
leftmost-innermost evaluation of expression trees  with  automatic
tail-call  elimination.  It also provides  an  (IMHO)  interesting
mechanism  for  handling lazy evaluation  by  means  of  so-called
"special forms," and it offers some features reminiscent of object-
oriented  programming  by  means of the "type  guard"  concept.  A
simple  symbolic  debugger, which is built into  the  interpreter,
allows you to trace the reductions performed during evaluations.

[...]
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-- 
Massimo Dentico