explicit signatures and default for integer literals

[Abraham Egnor]

Ghc can't assume "in this context" - the object file produced by
compilation could be linked into code that provides other instances.

Abe

On 5/31/05, Dinko Tenev <dinko.tenev at gmail.com> wrote:
> On 5/31/05, robert dockins <robdockins at fastmail.fm> wrote:
> >
> > Dinko Tenev wrote:
> >
> > >
> > > First we observe that, g = new . flip zip [0..], so, without the type
> > > specification, it has the general type (New [(a, b1)] b, Num b1, Enum
> > > b1) => [a] -> b, as reported by GHC.
> > >
> > > Then we infer from
> > >
> > >     (1) g :: (New [(u, v)] w, Num v, Enum v) => [u] -> w
> > >
> > > and
> > >
> > >     (2) instance New [(a, b)] (Map a b)
> > >
> > > that in (New [(u, v)] w), w can only be (Map u v)
> >
> > This step in the reasoning requires a functional dependency, which you
> > mentioned earlier you were unwilling to supply.  Without functional
> > dependencies w can, in fact, be something other than (Map u v).
> 
> We need to infer New [(u, v)] w, and the only thing we know so far is
> New [(a, b)] (Map a b).  In this context, what else could we possibly
> have for w besides (Map u v) ?
> 
> Cheers,
> 
> D. Tenev
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