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From: kend@data.UUCP (Ken Dickey)
Newsgroups: comp.lang.misc
Subject: Re^2: On whether C has first-class composable functions
Message-ID: <443@data.UUCP>
Date: 7 Jan 91 03:47:30 GMT
References: <1990Dec29.110202.3862@mathrt0.math.chalmers.se> <17557:Jan219:22:3191@kramden.acf.nyu.edu> <442@data.UUCP> <4408:Jan421:44:3391@kramden.acf.nyu.edu>
Organization: Microcosm, Beaverton, OR
Lines: 66

brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:

>In article <442@data.UUCP> kend@data.UUCP (Ken Dickey) writes:
>> There is an important property of "first-class" objects missing here.
>> A first-class object does not have to be named.  

>Do you have a reference? As always, I'm doing my best to use standard
>terminology; I just haven't seen any references that demand a syntactic
>restriction like that.

I believe that most references come from the Scheme literature.

The reference you want is Guy Steele's Masters thesis: "RABBIT: A
Compiler for SCHEME (A Study in Compiler Optimization)", MIT tech.
report: AI-TR-474, (May 1978).  [I suspect earlier references, but
have not yet found them].  From the introduction (pg 8):

  SCHEME also permits the treatment of functions as full flegded data
  objects; they may be passed as arguments, returned as values, made
  part of composite data structures, and notated as independent, unnamed
  ("anonymous") entities.  {Contrast this with most ALGOL-like
  languages, in which a function can be written only by declaring it and
  giving it a name; imagine being able to use an integer value only by
  giving it a name in a declaration!).
  
More recently, [Kent Dybvig, "The Scheme Programming Language",
Prentice Hall, 1987]

  ...procedures are not always named.  Instead, procedures are
  first-class data objects similar to strings or numbers;  identifiers
  are bound to procedures in the same way they are bound to other
  objects. 

I can dredge up more references if you like (most are at work and I am
at home).


>> By the way, what function would "apply(compose(compose,f),x);" return in C?
>> Strike "composable"?

>What are you talking about? 

I admit that my C syntax is a bit rusty.

>It doesn't make sense to compose a function
>that takes two arguments, at least not without a more general notation.
>I can't make heads or tails of your example.

Why should the number of arguments make a difference to composability?
One should certainly be able to compose the function COMPOSE!  {After
all it is a function, yes?}  So a composition of COMPOSE should be a
function.

So compose(compose,f) should return a function which takes another
function argument [e.g. x] and returns a function which takes, say, 2
arguments.  So I should be able to do something like compose the 2
functions, compose and f, to another function, x, to further
arguments: compose(compose,f)(x)(y,z).  C is rather weak, and I
presumed that you would need a help function, APPLY, to do this.


-Ken

[Someone else's signature, but it expresses the situation:]
 = The C Programming Language -- A language which combines the             =
 = flexibility of assembly language with the power of assembly language.   =