I have seen let-bindings with no parameters be detected as LNE. Thanks. This would mean that the comment is wrong.

Janek

HTH

On Wed, Oct 16, 2013 at 11:27 AM, Jan Stolarek wrote:

...

Hi all,

I'm trying to understand this:

1. Note [What is a non-escaping let] says that one of conditions of binding being a non-escaping let is non-updatability. 2. My understanding is that a if a binding has at least one parameter it is non-updatable, though I suspect that converse does not have to be true (lambdas) 3. Join-points are implemented using LNE bindings and I can imagine a join-points not having any parameters (and not being a lambda).

Three points above seem inconsistent - where does my reasoning go wrong? I suspect that the Note might be wrong and an updatable binding can in fact be a LNE binding.

Janek _______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://www.haskell.org/mailman/listinfo/ghc-devs

Yes, a join point should always have at least one argument, although it can be a zero-width argument that takes no registers to pass. (That's the State# RealWorld thing Simon mentions.) See Note [Join point abstraction] in Simplify.lhs. At one point the demand analyser was noticing that the argument was unused, and removing it, but I believe I fixed that. Does that resolve the question? Are any comments in the code inconsistent? Please clarify with Note [blah], and/or cross-reference to other Notes. Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Simon | Marlow | Sent: 17 October 2013 09:44 | To: Jan Stolarek; ghc-devs@haskell.org | Subject: Re: Non-escaping lets, join-points and binding updatability | | On 16/10/2013 18:27, Jan Stolarek wrote: | > Hi all, | > | > I'm trying to understand this: | > | > 1. Note [What is a non-escaping let] says that one of conditions of | binding being a non-escaping | > let is non-updatability. | > 2. My understanding is that a if a binding has at least one parameter | it is non-updatable, though | > I suspect that converse does not have to be true (lambdas) | > 3. Join-points are implemented using LNE bindings and I can imagine a | join-points not having any | > parameters (and not being a lambda). | | A join-point always has at least one argument. If there are no | arguments, then a dummy one of type State# RealWorld is added, to avoid | creating a thunk. | | Cheers, | Simon | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://www.haskell.org/mailman/listinfo/ghc-devs