SELECT CASE error

Forum for discussion about the documentation project.
speedfixer
Posts: 499
Joined: Nov 28, 2012 1:27
Location: California
Contact:

SELECT CASE error

Postby speedfixer » Jul 19, 2021 0:33

My first encounter of this error did not give me an error 62, but "error 61: Illegal inside functions ..."

I simplified until I got this correct error identification.

Because one could get a wrong error message, perhaps it should be mentioned on the wiki page that there may be no statements between the 'select case ...' statement and the first 'case x' statement. Seems obvious, but still - it happened.

In my case, it was a few lines of debugging code, easily moved somewhere else.

david
fxm
Moderator
Posts: 10548
Joined: Apr 22, 2009 12:46
Location: Paris suburbs, FRANCE

Re: SELECT CASE error

Postby fxm » Jul 19, 2021 8:27

Done:
KeyPgSelectcase → fxm [added note: No statement can be placed between the 'Select Case' statement and the first 'Case' statement]
counting_pine
Site Admin
Posts: 6302
Joined: Jul 05, 2005 17:32
Location: Manchester, Lancs

Re: SELECT CASE error

Postby counting_pine » Jul 22, 2021 14:11

Good find. An unhelpful error message might be worthy of a bug report, rather than just a documentation note.
fxm
Moderator
Posts: 10548
Joined: Apr 22, 2009 12:46
Location: Paris suburbs, FRANCE

Re: SELECT CASE error

Postby fxm » Jul 22, 2021 15:14

To be able to judge the unhelpful of the error message (61), it would be necessary to have the exact code which caused it.
This is not the first time that a (relevant) error message can hide another (equally relevant).

As for the note itself in the documentation, I do not think it is useless.
speedfixer
Posts: 499
Joined: Nov 28, 2012 1:27
Location: California
Contact:

Re: SELECT CASE error

Postby speedfixer » Jul 23, 2021 16:07

The note is good. Tracking down the EXACT cause not so easy.

I was calling a function in a function - with -mt

The -pp version is 2500 lines, with a LOT of precompiled static libs. Not so easy to get back to that same faulty error.

Also, I still get from time-to-time the console close failure where FB threads don't reset the console (Linux) correctly before stopping the program.
A segfault happens somewhere that has been very hard to pinpoint. (The program just closes somewhere in the destructors; only gdb reports the segfault.) So, the trigger for that incorrect error message could be a number of things.

Puzzling at first, but the line number was correct, so it only took me a few minutes to arrive at the correct error, so no problem. If it shows up again I will be more sensitive to the conditions and try a little more to catch the circumstances.

david
coderJeff
Site Admin
Posts: 3598
Joined: Nov 04, 2005 14:23
Location: Ontario, Canada
Contact:

Re: SELECT CASE error

Postby coderJeff » Jul 24, 2021 16:47

Changed in fbc-1.09, I tried to improve the error message:

Code: Select all

'' bad-stmt.bas

sub bad_select()
   dim x as integer = 1
   select case x
   print "oh no!"
   case 1
      print "1"
   end select
end sub

/'
FBC OUTPUT:
bad-stmt.bas(6) error 62: Statement in between SELECT and first CASE, found 'print' in 'print "oh no!"'
'/


Different error messages were being shown depending on if the SELECT was module level scope or procedure level scope.

If still missing the appropriate error message, please post a short code to show the problem.
fxm
Moderator
Posts: 10548
Joined: Apr 22, 2009 12:46
Location: Paris suburbs, FRANCE

Re: SELECT CASE error

Postby fxm » Jul 24, 2021 16:56

Well found !
dodicat
Posts: 7096
Joined: Jan 10, 2006 20:30
Location: Scotland

Re: SELECT CASE error

Postby dodicat » Jul 24, 2021 20:54

Code: Select all


sub selector()
   const x as integer = 122
   select case x
   const a=asc("z")
   const z= "oh no!"
   case a
      print z
   end select
end sub

selector()
sleep

 

 
coderJeff
Site Admin
Posts: 3598
Joined: Nov 04, 2005 14:23
Location: Ontario, Canada
Contact:

Re: SELECT CASE error

Postby coderJeff » Jul 25, 2021 2:07

@dodicat, interesting.
Appears to have been allowed for CONST and ENUM because neither generate code (only a symbol addition to the local scope) and SELECT CASE begins a new SCOPE. I can't imagine any user code in the wild depending on that. I'll add a couple of extra checks to CONST and ENUM to generate an error. Thanks.
dodicat
Posts: 7096
Joined: Jan 10, 2006 20:30
Location: Scotland

Re: SELECT CASE error

Postby dodicat » Jul 25, 2021 7:38

You can also have labels: (which work).
You can exit select there, and if the select case is in a sub/function you can have exit sub/function in there as well.
I would say that between constants, enums, the exit statements and labels you would have a hard job actually finding the first case after select case, if you so desired of course.
coderJeff
Site Admin
Posts: 3598
Joined: Nov 04, 2005 14:23
Location: Ontario, Canada
Contact:

Re: SELECT CASE error

Postby coderJeff » Aug 08, 2021 13:36

dodicat wrote:You can also have labels: (which work).
You can exit select there, and if the select case is in a sub/function you can have exit sub/function in there as well.


I appreciate the testing and feedback. Helps provide some polish to the compiler.

I've add the checks for labels and EXIT statements to generate an error between SELECT CASE and first CASE statement. I can't think of a use case where this makes sense to allow.

For anyone that is curious, what makes me nervous about this kind of change is that in a recursive descent parser is that there are many code paths to get to the same place in the parser's execution and the default tends to be that everything is permitted unless explicitly checked. I've added an explicit check to error for certain statements based on context. And because the test-suite is not exhaustive in proving out every scenario where labels, EXIT's, CONST's etc, should be allowed, there is the risk I've made a mistake and suddenly valid code no longer compiles. I don't think so ... but I look forward to the bug reports if a mistake has been made.

Return to “Documentation”

Who is online

Users browsing this forum: No registered users and 2 guests