`TEMP` phaser is not really implemented, but not a syntax error either

[lizmat]

After some spelunking, it appears that the TEMP phaser (as described in S06 - Temporization) was never implemented.

It looks like rakudo/rakudo@973df80cfad07b68da9 in May 2012 was the last real work in that area, and nothing happened after that. However, the TEMP phaser is valid syntax at the moment:

$ raku -e 'TEMP say "temp"'

parses ok, but there is no way to actually get that TEMP phaser to execute.

The fact that nobody has felt the need to actually implement it since then, indicates to me that it is not needed. The temp / let / KEEP phaser / UNDO phaser provide all of the possibilities that are needed.

Removal would be simple. However, there are a few TODO'd roast tests that would need to be changed as well.

So the proposal is to do just that: remove the TODO'd roast tests, and make TEMP say "temp" an error (possibly NYI, or perhaps a DEPRECATED message?)

[ab5tract]

I agree completely except that I think that there is an argument to produce a worry instead of an outright error.

The worry text can be comprehensive about explaining that TEMP is both unimplemented and deprecated.

I expect any code actually using TEMP will be on the older side of things (an assumption based on temporal proximity to the specification process). IMO it would be nice to let those keep running without modification if we can.

[lizmat]

How about:

% git diff
diff --git a/src/Perl6/Actions.nqp b/src/Perl6/Actions.nqp
index e282956e0..4cccc349c 100644
--- a/src/Perl6/Actions.nqp
+++ b/src/Perl6/Actions.nqp
@@ -2519,6 +2519,10 @@ class Perl6::Actions is HLL::Actions does STDActions {
         }
     }
 
+    method statement_prefix:sym<TEMP>($/) {
+        $/.worry("The TEMP phaser will never be implemented.\nPlease remove to prevent breakage in future language versions.");
+    }
+

[coke]

Let's use deprecation then we can remove it cleanly at the language boundary.

[lizmat]

Problem with deprecation, is that it's runtime and will only be shown after the program has completed. It would need to codegen:

DEPRECATED("temp or let prefix operators",:what("TEMP phaser"))

which would produce:

Saw 1 occurrence of deprecated code.
================================================================================
TEMP phaser seen at:
  -e, line 1
Please use temp or let prefix operators instead.
--------------------------------------------------------------------------------
Please contact the author to have these occurrences of deprecated code
adapted, so that this message will disappear!

Showing the deprecation at compile would be an option as well, but it would be far easier to implement a worry then.

Hence my preference for a worry at compile time.