[Haskell-cafe] Are newtypes optimised and how much?

wren ng thornton wren at freegeek.org
Wed Oct 20 19:11:25 EDT 2010

On 10/20/10 7:07 PM, wren ng thornton wrote:
> On 10/20/10 7:09 AM, Simon Peyton-Jones wrote:
>> Yes, you can freely use Foo/unFoo. There's no runtime penalty. (In the
>> jargon of GHC's intermediate language, Foo and unFoo translate to
>> *type-safe casts*, which generate no executable code.
> When does the conversion to type-safe casts occur relative to other
> optimizations (namely, rewrite rules)?

That is, I know that rewrite rules operate on the source language not on 
Core, but to what extent does that mean that type-safe casts inhibit the 
firing of rules?

Live well,

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