Re: OT: What was the first programming language to use 'generics'?...

[David Trudgett <wpower@zeta.org.au.nospamplease>]

"Martin Dowie" <martin.dowie@baesystems.com> writes:

> ...and were they called 'generics'?
>
> Not Ada but I just know /someone/ here will know this! ;-)
>
>

Probably (given I'm not a language historian) Lisp code macros were
the first, except for a couple of provisos: (a) Lisp never had the
strong static typing that Ada has, so Lisp macros weren't invented to
solve the same problem as Ada generics; and (b) Lisp macros are more
general than Ada generics in the sense that they allow essentially
arbitrary code (not text) generation (every Ada programmer's
nightmare? ;-)).

I'm only a Lisp learner myself (same as I'm learning Ada), but for
those who may be interested, the following is a very simple example of
a template style macro in Common Lisp (lifted from Peter Herth's LTk
package):

(defmacro with-ltk (&rest body)
  `(let ((*wish* nil)
         (ltk::*callbacks* (make-hash-table :test #'equal))
         (ltk::*counter* 1)
         (ltk::*event-queue* nil))
     (start-wish)
     ,@body
     (mainloop)))

This defines a macro called 'with-ltk' that takes a list of parameters
which it collectively (in this case) refers to as 'body'. The rest is
a code template (introduced by the backtick), into which the arguments
to 'with-ltk' are inserted (the ',@body' business). So, 'with-ltk' is
essentially just a simple code wrapper, and therefore not a
particularly fascinating example.

With this macro facility, the programmer can write a simple (or not!)
piece of code which generates different "parse trees" (I believe
that's the terminology) according to the context, for a similar effect
to Ada generics, which result in the generation of varying object code
according to context.

David


-- 

David Trudgett
http://www.zeta.org.au/~wpower/

As a computer, I find your faith in technology amusing.