From: Adam Beneschan <adam@irvine.com>
Subject: Re: Unary operator after binary operator: legal or not?
Date: Mon, 30 Jul 2007 17:22:11 -0700
Date: 2007-07-30T17:22:11-07:00 [thread overview]
Message-ID: <1185841331.637593.83960@x40g2000prg.googlegroups.com> (raw)
In-Reply-To: <KYtri.46105$Fc.35820@attbi_s21>
On Jul 30, 3:52 pm, "Jeffrey R. Carter"
<spam.jrcarter....@acm.nospam.org> wrote:
> Here's something confusing I encountered:
>
> with Ada.Strings.Unbounded;
>
> function Xyz (Left, Right : in Ada.Strings.Unbounded.Unbounded_String)
> return String is
> function "+" (Right : in Ada.Strings.Unbounded.Unbounded_String)
> return String renames Ada.Strings.Unbounded.To_String;
> begin -- Xyz
> if +Left <= +Right then
> return +Left & +Right;
> -- ^ Error reported here.
> end if;
> end Xyz;
>
> A compiler reports "missing operand", referencing the space after the "&".
>
> Why then does it accept the comparison in the previous line? Both are
>
> +Left [binary operator] +Right
I think that was a deliberate decision. See the BNF in 4.4. The
operands of "and", "and then", "or", "or else", "xor", "in", or
relational operators are <simple_expression>. The definition of a
<simple_expression> is
[unary_adding_operator] term {binary_adding_operator term}
A unary_adding_operator is part of the syntax of <simple_expression>
but not of <term>, so the consequences is that the right operator of a
binary_adding_operator (or a multiplying_operator, or "**" or "abs" or
"not") can't start with a unary adding operator, unless you
parenthesize it. But the right operand of a relational operator or
one of the logical operators I listed above *can* start with a unary
adding operator.
-- Adam
next prev parent reply other threads:[~2007-07-31 0:22 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-30 22:52 Unary operator after binary operator: legal or not? Jeffrey R. Carter
2007-07-30 23:39 ` Markus E.L.
2007-07-31 0:22 ` Adam Beneschan [this message]
2007-07-31 21:52 ` Jeffrey R. Carter
2007-07-31 8:01 ` anon
2007-07-31 8:16 ` Unary operator after binary operator: legal or not? => Compiler Error anon
2007-07-31 8:38 ` AW: Unary operator after binary operator: legal or not? => CompilerError Grein, Christoph (Fa. ESG)
2007-07-31 15:05 ` Unary operator after binary operator: legal or not? => Compiler Error Robert A Duff
2007-07-31 15:39 ` Dmitry A. Kazakov
2007-07-31 15:53 ` Robert A Duff
2007-07-31 17:02 ` Georg Bauhaus
2007-07-31 19:17 ` Adam Beneschan
2007-08-01 7:16 ` Maciej Sobczak
2007-08-01 15:23 ` Adam Beneschan
2007-07-31 20:59 ` Robert A Duff
2007-08-01 7:24 ` Georg Bauhaus
2007-08-01 8:02 ` Dmitry A. Kazakov
2007-08-01 8:17 ` AW: Unary operator after binary operator: legal or not? => CompilerError Grein, Christoph (Fa. ESG)
2007-08-01 10:10 ` Ian Clifton
2007-08-01 9:34 ` Unary operator after binary operator: legal or not? => Compiler Error Georg Bauhaus
2007-08-01 21:51 ` Jeffrey R. Carter
2007-07-31 17:52 ` Dmitry A. Kazakov
2007-08-02 20:44 ` Charles Lindsey
2007-08-03 7:48 ` Stuart
2007-08-03 7:51 ` Dmitry A. Kazakov
2007-07-31 23:22 ` anon
2007-08-01 0:13 ` Adam Beneschan
2007-08-01 6:20 ` Unary operator after binary operator: legal or not? => Illegal anon
2007-08-01 5:34 ` AW: Unary operator after binary operator: legal or not? => CompilerError Grein, Christoph (Fa. ESG)
2007-08-01 6:46 ` To := Grein, Christoph (Fa. ESG) anon
2007-08-01 7:11 ` AW: " Grein, Christoph (Fa. ESG)
2007-08-02 6:52 ` anon
2007-08-02 8:56 ` AW: " Grein, Christoph (Fa. ESG)
2007-08-02 22:29 ` Markus E.L. 2
2007-08-02 23:02 ` tmoran
2007-08-02 23:11 ` Ed Falis
2007-08-02 23:34 ` Markus E.L. 2
2007-08-03 4:42 ` AW: " Grein, Christoph (Fa. ESG)
2007-08-02 22:28 ` Markus E.L. 2
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