Pragmas
# Lars T Hansen (18 years ago)
Pragmas are invariably lexically scoped.
Some pragmas are probably more useful at the top level, "use strict" is among these. One pattern we think might develop is "use strict" at the top level, followed by "use standard" inside some blocks where strict mode gets in the way (if only temporarily during program development).
Pragmas are invariably lexically scoped. Some pragmas are probably more useful at the top level, "use strict" is among these. One pattern we think might develop is "use strict" at the top level, followed by "use standard" inside some blocks where strict mode gets in the way (if only temporarily during program development). --lars On Nov 12, 2007 10:18 AM, Peter Hall <peter.hall at memorphic.com> wrote: > What is the scope of a pragma such as that? Is it just the current > lexical scope, like a "use namespace" statement, or does it change the > behaviour for the entire program? If it's the latter, isn't there a > compatibility problem between libraries? If it's the former, do you > anticipate that es4 programs will be littered with "use strict" > pragmas? Think Fortran and "implicit none".... > > I assume this has been previously discussed, but I couldn't find it, > so apologies if that is the case. > > Peter > > > On 11/12/07, Brendan Eich <brendan at mozilla.org> wrote: > > On Nov 12, 2007, at 9:00 AM, Jonathan Watt wrote: > > > > > Hi, > > > > > > As I understand it the reason assignment to ReadOnly properties > > > fails silently > > > is that there was no try-catch prior to ECMAScript 3. > > > > Right. Netscape 2 reported a fatal error, but during ES1 > > standardization we agreed to go with silence is (golden|deadly). > > > > > Could/will edition 4 require an exception to be thrown in strict mode? > > > > Overtly incompatible, also highly desirable. So opt-in versioning > > could enable this, but it's one more migration headache (see recent > > exchange between Mark Miller and myself). An alternative would be a > > pragma of some sort: > > > > use readonly error > > > > or perhaps > > > > use readonly throw > > > > We try to make pragmas more readable, sometimes with an extra word; > > not sure this is the best way to phrase it still, but the idea would > > be to enable throwing of a ReadOnlyError on assignment to a ReadOnly > > property. Comments? > > > > /be > > > > _______________________________________________ > > Es4-discuss mailing list > > Es4-discuss at mozilla.org > > https://mail.mozilla.org/listinfo/es4-discuss > > > _______________________________________________ > Es4-discuss mailing list > Es4-discuss at mozilla.org > https://mail.mozilla.org/listinfo/es4-discuss >
# Peter Hall (18 years ago)
Also, there is a minor bug [1] with the pragma syntax:
Pragma : UsePragma SemicolonFull ImportPragma SemicolonFull
UsePragma : use PragmaItems SemicolonFull
resulting in two semicolons being required after a "use" pragma.
Peter
Also, there is a minor bug [1] with the pragma syntax: Pragma : UsePragma SemicolonFull ImportPragma SemicolonFull UsePragma : use PragmaItems SemicolonFull resulting in two semicolons being required after a "use" pragma. Peter [1] http://wiki.ecmascript.org/doku.php?id=proposals:syntax_for_pragmas On 11/12/07, Peter Hall <peter.hall at memorphic.com> wrote: > What is the scope of a pragma such as that? Is it just the current > lexical scope, like a "use namespace" statement, or does it change the > behaviour for the entire program? If it's the latter, isn't there a > compatibility problem between libraries? If it's the former, do you > anticipate that es4 programs will be littered with "use strict" > pragmas? Think Fortran and "implicit none".... > > I assume this has been previously discussed, but I couldn't find it, > so apologies if that is the case. > > Peter > > > On 11/12/07, Brendan Eich <brendan at mozilla.org> wrote: > > On Nov 12, 2007, at 9:00 AM, Jonathan Watt wrote: > > > > > Hi, > > > > > > As I understand it the reason assignment to ReadOnly properties > > > fails silently > > > is that there was no try-catch prior to ECMAScript 3. > > > > Right. Netscape 2 reported a fatal error, but during ES1 > > standardization we agreed to go with silence is (golden|deadly). > > > > > Could/will edition 4 require an exception to be thrown in strict mode? > > > > Overtly incompatible, also highly desirable. So opt-in versioning > > could enable this, but it's one more migration headache (see recent > > exchange between Mark Miller and myself). An alternative would be a > > pragma of some sort: > > > > use readonly error > > > > or perhaps > > > > use readonly throw > > > > We try to make pragmas more readable, sometimes with an extra word; > > not sure this is the best way to phrase it still, but the idea would > > be to enable throwing of a ReadOnlyError on assignment to a ReadOnly > > property. Comments? > > > > /be > > > > _______________________________________________ > > Es4-discuss mailing list > > Es4-discuss at mozilla.org > > https://mail.mozilla.org/listinfo/es4-discuss > > >
# Jeff Dyer (18 years ago)
Got it.
Got it. Thanks! Jd On 11/12/07 10:25 AM, Peter Hall wrote: > Also, there is a minor bug [1] with the pragma syntax: > > Pragma : > UsePragma SemicolonFull > ImportPragma SemicolonFull > > UsePragma : > use PragmaItems SemicolonFull > > > resulting in two semicolons being required after a "use" pragma. > > > Peter > > > [1] http://wiki.ecmascript.org/doku.php?id=proposals:syntax_for_pragmas > > > > > > On 11/12/07, Peter Hall <peter.hall at memorphic.com> wrote: >> What is the scope of a pragma such as that? Is it just the current >> lexical scope, like a "use namespace" statement, or does it change the >> behaviour for the entire program? If it's the latter, isn't there a >> compatibility problem between libraries? If it's the former, do you >> anticipate that es4 programs will be littered with "use strict" >> pragmas? Think Fortran and "implicit none".... >> >> I assume this has been previously discussed, but I couldn't find it, >> so apologies if that is the case. >> >> Peter >> >> >> On 11/12/07, Brendan Eich <brendan at mozilla.org> wrote: >>> On Nov 12, 2007, at 9:00 AM, Jonathan Watt wrote: >>> >>>> Hi, >>>> >>>> As I understand it the reason assignment to ReadOnly properties >>>> fails silently >>>> is that there was no try-catch prior to ECMAScript 3. >>> >>> Right. Netscape 2 reported a fatal error, but during ES1 >>> standardization we agreed to go with silence is (golden|deadly). >>> >>>> Could/will edition 4 require an exception to be thrown in strict mode? >>> >>> Overtly incompatible, also highly desirable. So opt-in versioning >>> could enable this, but it's one more migration headache (see recent >>> exchange between Mark Miller and myself). An alternative would be a >>> pragma of some sort: >>> >>> use readonly error >>> >>> or perhaps >>> >>> use readonly throw >>> >>> We try to make pragmas more readable, sometimes with an extra word; >>> not sure this is the best way to phrase it still, but the idea would >>> be to enable throwing of a ReadOnlyError on assignment to a ReadOnly >>> property. Comments? >>> >>> /be >>> >>> _______________________________________________ >>> Es4-discuss mailing list >>> Es4-discuss at mozilla.org >>> https://mail.mozilla.org/listinfo/es4-discuss >>> >> > _______________________________________________ > Es4-discuss mailing list > Es4-discuss at mozilla.org > https://mail.mozilla.org/listinfo/es4-discuss
# Peter Hall (18 years ago)
On the surface, that sounds like it makes sense. But if I'm writing an application in strict mode, that uses a pre-existing library, will I have to edit that library to add "use standard" to every file?
"Inheriting" the pragma is not straightforward unless you inherit only from the program entry point. After that, it doesn't seem possible to derive a well-defined ancestry tree, since source code may be referenced from many different locations, often cyclically.
Peter
On the surface, that sounds like it makes sense. But if I'm writing an application in strict mode, that uses a pre-existing library, will I have to edit that library to add "use standard" to every file? "Inheriting" the pragma is not straightforward unless you inherit only from the program entry point. After that, it doesn't seem possible to derive a well-defined ancestry tree, since source code may be referenced from many different locations, often cyclically. Peter On 11/12/07, Lars T Hansen <lth at acm.org> wrote: > Pragmas are invariably lexically scoped. > > Some pragmas are probably more useful at the top level, "use strict" > is among these. One pattern we think might develop is "use strict" > at the top level, followed by "use standard" inside some blocks where > strict mode gets in the way (if only temporarily during program > development). > > --lars > > On Nov 12, 2007 10:18 AM, Peter Hall <peter.hall at memorphic.com> wrote: > > What is the scope of a pragma such as that? Is it just the current > > lexical scope, like a "use namespace" statement, or does it change the > > behaviour for the entire program? If it's the latter, isn't there a > > compatibility problem between libraries? If it's the former, do you > > anticipate that es4 programs will be littered with "use strict" > > pragmas? Think Fortran and "implicit none".... > > > > I assume this has been previously discussed, but I couldn't find it, > > so apologies if that is the case. > > > > Peter > > > > > > On 11/12/07, Brendan Eich <brendan at mozilla.org> wrote: > > > On Nov 12, 2007, at 9:00 AM, Jonathan Watt wrote: > > > > > > > Hi, > > > > > > > > As I understand it the reason assignment to ReadOnly properties > > > > fails silently > > > > is that there was no try-catch prior to ECMAScript 3. > > > > > > Right. Netscape 2 reported a fatal error, but during ES1 > > > standardization we agreed to go with silence is (golden|deadly). > > > > > > > Could/will edition 4 require an exception to be thrown in strict mode? > > > > > > Overtly incompatible, also highly desirable. So opt-in versioning > > > could enable this, but it's one more migration headache (see recent > > > exchange between Mark Miller and myself). An alternative would be a > > > pragma of some sort: > > > > > > use readonly error > > > > > > or perhaps > > > > > > use readonly throw > > > > > > We try to make pragmas more readable, sometimes with an extra word; > > > not sure this is the best way to phrase it still, but the idea would > > > be to enable throwing of a ReadOnlyError on assignment to a ReadOnly > > > property. Comments? > > > > > > /be > > > > > > _______________________________________________ > > > Es4-discuss mailing list > > > Es4-discuss at mozilla.org > > > https://mail.mozilla.org/listinfo/es4-discuss > > > > > _______________________________________________ > > Es4-discuss mailing list > > Es4-discuss at mozilla.org > > https://mail.mozilla.org/listinfo/es4-discuss > > > _______________________________________________ > Es4-discuss mailing list > Es4-discuss at mozilla.org > https://mail.mozilla.org/listinfo/es4-discuss >
What is the scope of a pragma such as that? Is it just the current lexical scope, like a "use namespace" statement, or does it change the behaviour for the entire program? If it's the latter, isn't there a compatibility problem between libraries? If it's the former, do you anticipate that es4 programs will be littered with "use strict" pragmas? Think Fortran and "implicit none"....
I assume this has been previously discussed, but I couldn't find it, so apologies if that is the case.
Peter