Sounds like the interpreter wants to know the value of the last statement it executes.

say returns something it can work with.
my doesn't or this my creates doesn't.

Pure speculation based solely on what you posted.

That sounds right to me.

16:31 moritz_       rakudo: say |(1, 2, 3)                            
+                                                                     
+                                                                     
+                                                                     
+                                                    
16:31 exp_evalbot   rakudo r28145 OUTPUT[␤get_bool() not implemented
+ in class 'Junction'␤current instr.: 'parrot;PCT::HLLCompiler;comm
+and_line' pc 1288 (src/PCT/HLLCompiler.pir:688)␤                   
+                                                                     
+                                                    
16:31 moritz_       pugs: say |(1, 2, 3)                              
+                                                                     
+                                                                     
+                                                                     
+                                                    
16:31 exp_evalbot   OUTPUT[123␤]                                    
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+                                                                     
+                                                                     
+                                                    
16:32 [particle]    seems rakudo doesn't have prefix:|                
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+                                                                     
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+                                                    
16:32 [particle]    or is it the |() op?                              
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+                                                                     
+                                                                     
+                                                    
16:32 moritz_       prefix:|                                          
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+                                                                     
+                                                                     
+                                                    
16:34 diakopter     wow; that was almost trivial                      
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+                                                                     
+                                                                     
+                                                    
16:34 moritz_       diakopter: what, adding prefix:| to yap6?         
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+                                                                     
+                                                                     
+                                                    
16:35 diakopter     (adding infinite recursion detection to the recurs
+ive-descent-parser framework)
[download]

But why

perl6 -e "my IO $fh; say $fh.what;"
[download]

could be run successfully?

---

I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction

Maybe there is already detection of unused variables programmed into rakudo. And that detection does an additional check on the IO object.