NoMonomorphismRestriction

[Simon Peyton-Jones]

| > I've made a ticket and proposal page for removing the monomorphism
| > restriction:	
| >    http://hackage.haskell.org/trac/haskell-prime/ticket/131
| >    http://hackage.haskell.org/trac/haskell-prime/wiki/NoMonomorphismRestriction
| 
| I think if we do this we really have to do
| 
| http://hackage.haskell.org/trac/haskell-prime/wiki/SpecifyPatternBindingSemantics

Apropos of the MR, I'd like to invite you to read

	Let should not be generalised
	Dimitrios Vytiniotis, Simon Peyton Jones, and Tom Schrijvers
	Submitted to POPL 2010
	http://research.microsoft.com/en-us/um/people/simonpj/papers/constraints/index.htm

Abstract: From the dawn of time, all derivatives of the classic Hindley-Milner type system have supported implicit generalisation of local let-bindings. Yet, as we will show, for more sophisticated type systems implicit let-generalisation imposes a disproportionate complexity burden. Moreover, it turns out that the feature is very seldom used, so we propose to eliminate it. The payoff is a substantial simplification, both of the specification of the type system, and of its implementation.


The paper makes the (somewhat radical) case for not generalising local bindings at all; which would at a stroke remove most of the issues of the MR.  (We'd still need to think about the top level.)

We'd love to know what any of you think of the idea.

Simon

| -----Original Message-----
| From: haskell-prime-private-bounces at haskell.org [mailto:haskell-prime-private-
| bounces at haskell.org] On Behalf Of Simon Marlow
| Sent: 27 July 2009 11:13
| To: haskell-prime at haskell.org; haskell-prime-private at haskell.org
| Subject: Re: [Haskell'-private] NoMonomorphismRestriction
| 
| On 25/07/2009 16:28, Ian Lynagh wrote:
| 
| > I've made a ticket and proposal page for removing the monomorphism
| > restriction:	
| >    http://hackage.haskell.org/trac/haskell-prime/ticket/131
| >    http://hackage.haskell.org/trac/haskell-prime/wiki/NoMonomorphismRestriction
| 
| I think if we do this we really have to do
| 
| http://hackage.haskell.org/trac/haskell-prime/wiki/SpecifyPatternBindingSemantics
| 
| Which is not strictly speaking a change, but is a necessary
| clarification if the MR is removed.  I believe the conclusion we came to
| in March/April 2008 was to do this.
| 
| Cheers,
| 	Simon
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