Add tail recursion optimization

[DartBot]

This issue was originally filed by paulp...@gmail.com

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Tailrec optimization is a well-known feature of functional languages.

I propose to add support for it in dart.

[DartBot]

This comment was originally written by mprz1024@gmail.com

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I think this is one of the most important features Dart is missing. Tail call elimination, or a subset of this functionality — tail recursion elimination — supports the implementation of certain algorithms in a recursive way that is easier to think for some programmers (especially those coming from mathemathical or more formal computing science background) and allows for the implementation of parts of programs without side effects, which has been proven to be less error-prone. It's a feature from many functional programming languages we would love to have in Dart.

Please note that this feature hurts no one: people without the understanding of it will simply not benefit from it, but it will not make their lives harder.

[dgrove]

Removed Type-Defect label.
Added Type-Enhancement, Area-Language labels.

[DartBot]

This comment was originally written by drfibonacci@google.com

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Added Triaged label.

[gbracha]

Tail recursion elimination needs to be balanced against issues like debugging. There are ways to do this, and maybe at some point we will do something, but honestly, it won't be very soon, if ever.

[gbracha]

Set owner to @gbracha.

[floitschG]

Just to comment on the "this feature hurts no one". Aside from the common debug arguments there is (or can be) also a runtime cost associated with them. Tail call optimization precludes some calling-conventions (which a VM normally can chose freely). I would compare it to disallowing --fomit-frame-pointer for gcc.

[DartBot]

This comment was originally written by martin.elsman...@gmail.com

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I would suggest adding tail-call optimization support quickly. For programming with continuations and other advanced control operators, tail-call optimization is essential. Tail-call optimization is also necessary for programming in a functional style using tail-recursion. Finally, DART could take off quickly as a target language for compilers for functional language compilers such as Hop, SMLtoJs, AFAX, and Links, to name just a few.

[polux]

Let me just stress that with popular frameworks like Node.js who rely heavily on a continuation passing style, the tail call optimization does seem more than relevant.

[larsbak]

An important goal of Dart is ensuring we can generate efficient JavaScript code.
Adding tail-call optimizations or non-local-returns for that matter will deviate from this goal.
If you want to use Dart as a target language, one option is apply inlining and generating large methods will label jumps. This is no different from using Java or JavaScript.

[DartBot]

This comment was originally written by LuoZhongYao...@gmail.com

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This is a Bug?
main(){
   int a;
   print(a is num);
}

Run retunr is false.

main(){
   int a;
   print(a is num); // Prints false
}

This is not a bug. 'a' is initialized to null and (null is num) returns false.

(Please file a new issue for different bug reports)

[anders-sandholm]

Added apr30-triage label.

[anders-sandholm]

Removed apr30-triage label.

[anders-sandholm]

Added triage1 label.

[anders-sandholm]

Added this to the Later milestone.
Removed triage1 label.