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digitalmars.D.bugs - [Issue 200] New: Statement *must* follow label

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=200

           Summary: Statement *must* follow label
           Product: D
           Version: 0.160
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: ericanderton yahoo.com


This one is pretty simple.  The parser seems to think that the only valid way
to use a label is if a statement directly follows it.  But shouldn't a label be
valid all by itself, if its the last line of a scope?

void main(){
        x:
}

test.d(3): found '}' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement
test.d(3): found 'EOF' instead of statement

The workaround for this one is dead simple: just use a ';' right after the
label.  IMO, that doesn't look like valid code.

void main(){
        x: ;
}


-- 
Jun 16 2006
next sibling parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
d-bugmail puremagic.com wrote:
 This one is pretty simple.  The parser seems to think that the only valid way
 to use a label is if a statement directly follows it.  But shouldn't a label be
 valid all by itself, if its the last line of a scope?
 
 void main(){
         x:
 }

[snip]
 The workaround for this one is dead simple: just use a ';' right after the
 label.  IMO, that doesn't look like valid code.

Or, you know, you could just use "return" instead of "goto x" :P
Jun 16 2006
parent reply pragma <pragma_member pathlink.com> writes:
In article <e6v4p9$c5f$1 digitaldaemon.com>, Frits van Bommel says...
d-bugmail puremagic.com wrote:
 This one is pretty simple.  The parser seems to think that the only valid way
 to use a label is if a statement directly follows it.  But shouldn't a label be
 valid all by itself, if its the last line of a scope?
 
 void main(){
         x:
 }

[snip]
 The workaround for this one is dead simple: just use a ';' right after the
 label.  IMO, that doesn't look like valid code.

Or, you know, you could just use "return" instead of "goto x" :P

Not always. :) The example in the bug report is merely the most simple case for Walter's sake Here's a real-world example: http://www.dsource.org/projects/ddl/browser/trunk/enki/EnkiParser.d#L91 The above shows a different variation of a workaround: using "{}". But the problem still stands. The code generator needs a way to provide a way to jump to a known pass/fail point where it is known that there are no other instructions that could generate side-effects. Each "{}" closure also maps to a particular production in the input grammar, and has its own variables for input capture and rewinding the parse position - that's how I found #199 as well. - EricAnderton at yahoo
Jun 16 2006
parent BCS <BCS pathlink.com> writes:
pragma wrote:
 In article <e6v4p9$c5f$1 digitaldaemon.com>, Frits van Bommel says...
Or, you know, you could just use "return" instead of "goto x" :P

Not always. :) The example in the bug report is merely the most simple case for Walter's sake Here's a real-world example: http://www.dsource.org/projects/ddl/browser/trunk/enki/EnkiParser.d#L91 The above shows a different variation of a workaround: using "{}". But the problem still stands. The code generator needs a way to provide a way to jump to a known pass/fail point where it is known that there are no other instructions that could generate side-effects. Each "{}" closure also maps to a particular production in the input grammar, and has its own variables for input capture and rewinding the parse position - that's how I found #199 as well. - EricAnderton at yahoo

any reason to not allow this? foo: { // bail out of this scope if(i==0) break foo; writef("i!=0\n"); (i<0)?1++:i--; // same effect as continue so no need for that goto foo; } Yes its a bit contrived, but the idea could make some more complicated code (auto or hand generated) a bit cleaner. I have a few times put something in a function just so that a return could be used to leave the scope.
Jun 17 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=200


smjg iname.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smjg iname.com




------- Comment #1 from smjg iname.com  2006-06-19 09:42 -------
The spec gives:

    LabelledStatement:
        Identifier ':' Statement

i.e. a label prefixes a statement - it doesn't act as a statement by itself.

(In reply to comment #0)
 The workaround for this one is dead simple: just use a ';' right after the
 label.  IMO, that doesn't look like valid code.

Indeed, it isn't according to the spec, and for good reasons. Use an empty BlockStatement instead. void main() { x: {} } --
Jun 19 2006
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=200


bugzilla digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED




------- Comment #2 from bugzilla digitalmars.com  2006-06-30 20:30 -------
Fixed DMD 0.162
(changed spec to allow ';' as empty statement after label)


-- 
Jun 30 2006