On Thursday 20 November 2008 22:57:13 marlenemiller71 wrote:
> > In both cases, the reason is that exhaustiveness checking is based
> > only on the type of the expression, not on its value.
>
> Is it correct to explain let-binding for this syntax
>
> let <pattern> = <expression1> in <expression2>
>
> as the type inference mechanism computes type T1 of <pattern> and type
> T2 of <expression1> inferring the type of variables in <pattern> using
> T2, and then T1 must be the same as T2?

Essentially, yes. Note that "T1 must be the same as T2" should strictly be "T1
is unified with T2".

I found it very instructive to implement a simple type inferencer in OCaml, to
understand how type inference works. That gives you a much better idea of how
to interpret type errors when things go wrong in OCaml as well.

--
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e

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