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From: dobrien@seas.gwu.edu (David O'Brien)
Newsgroups: comp.lang.ada
Subject: Re: "Subtract C, add Ada"
Date: 14 Jan 1995 00:24:13 GMT
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Laurent Gasser (gasser@masg1.epfl.ch) wrote:
: In article <3f4mbe$rud@cronkite.seas.gwu.edu>, dobrien@seas.gwu.edu (David O'Brien) writes:
: |> R.A.L Williams (bill@valiant) wrote:
: |> : My experience of writing software and running software projects in C
: |> : highlights four common low-level C errors:
: |> :   1. = instead of == and vice versa
: |> 
: |> I have to wonder.  What if C defined the logical equals operator to be
: |> "=" and the assignment operator to be ":=" just like Ada, Algol, Pascal,
: |> Modula-x, etc?  Would this error still exist???

: The problem is in the language definition, not in the choice of symbols.
: C is one of the rare language I use to allow having an assignment after 
: the if statement.  All other languages only allow for a boolean test.

Yep, that's my point.  The argument of character choice really isn't what
is at the essence of the problem.  Rather it is the language definition.


: I never saw a good reason for allowing this.

Simply the paradigm of C that *every* statement has a value.  And C has
no special logical values.  So C has "values are values" akin to Ford's
offering of the Model-T, "any colour you want, as long as it's black".
I'm guessing Ritchie did this for the same reason as Henry Ford - to
simply things.  Which gave us the situation we have.

In most languages the grammar would be:

	conditional_statement ::=  if <logical_expression> then

Which in C becomes:

	conditional_statement ::=  if ( <expression> ) <statement>

and thus ``<expression>'' must include ``<lvalue> = <expression>''.

-- David O'Brien	(dobrien@seas.gwu.edu)