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From: hal@cornell.UUCP (Hal Perkins)
Newsgroups: net.lang
Subject: Re: I/O operations in programming languages
Message-ID: <5189@cornell.UUCP>
Date: Tue, 30-Aug-83 21:24:08 EDT
Article-I.D.: cornell.5189
Posted: Tue Aug 30 21:24:08 1983
Date-Received: Wed, 31-Aug-83 23:22:55 EDT
References: <666@mit-eddie.UUCP>, <110@csd1.UUCP>, <1796@allegra.UUCP>
Organization: Cornell Computer Science
Lines: 55

Something's not quite right here.  The claim is that the C language
contains I/O operations because any language that can be used to write
useful, portable programs must contain I/O operations.  I don't agree,
and I don't think the argument holds together.

First, I think it is reasonably obvious that the C programming language
itself does not contain I/O commands in the sense that FORTRAN, COBOL,
PL/I or Pascal do.  In these languages, I/O operations have special
syntactic forms and semantics that, in most cases, could not be defined
by procedures or functions written in the language.  For example, the
Pascal read, readln, write, and writeln operations can accept any number
of parameters of any of the basic scalar types, and a special notation is
available to specify the format of numbers printed by write and writeln.
These procedures absolutely cannot be defined using the standard Pascal
language; they have to be specified in the language definition or they
couldn't be there in their present form.

In C and Ada, among other examples, there are no special forms for I/O
commands.  So I claim that these languages do not contain I/O.  How then
is it possible to use these languages to write useful programs?  The
answer is that there are standard libraries or packages that provide I/O
operations.  Furthermore, virtually every implementation of these languages
includes the an implementation of the standard I/O packages.  For C, this
is customarily the standard set of I/O routines described in Kernighan &
Ritchie.  For Ada, DoD has decreed that all certified Ada implementations
must provide certain standard I/O packages.

So it seems to me there is no problem with the statement that C does not
contain any I/O.  The incorrect statement is the one that claims that any
useful programming language must contain I/O--otherwise programs cannot
communicate with the world.  The correct version is that either the language
must contain I/O statements OR ELSE a standard package of I/O routines must
be available with all implementations of the language.  This is one of the
reasons that ALGOL 60 never caught on.  ALGOL 60 contains no I/O.  Nothing
wrong with that--C has demonstrated that a language without I/O statements
is perfectly usable.  But the ALGOL 60 community never defined a single,
universally available, set of I/O procedures, so there was no way to write
a portable program that communicated with the outside world.  (Actually,
attempts were made to specify a standard ALGOL 60 I/O package, but these
were never widely adopted.  I suspect that it is at least as difficult to
standardize the I/O package definitions as it is to standardize language
definitions.  In the case of C, the Unix environment has been so closely
associated with the language that it became the I/O standard by default.)

To close this excessively long note, it seems to me that languages
should not contain I/O commands because this helps to keep the language
definition short and comprehensable.  But it is equally important to
define a basic set of I/O operations that are universally available with
every implementation.  Defining a good basic set of I/O operations is a
difficult design problem.  Separating this problem from the basic language
can only help; it simplifies the number of things that must be designed
at the same time.

Hal Perkins                         UUCP: {decvax|vax135|...}!cornell!hal
Cornell Computer Science            ARPA: hal@cornell  BITNET: hal@crnlcs