[Haskell-cafe] syntactic sugar for heterogeneous lists

[Alberto G. Corona]

Yep, this is nice and flexible, but it is not standard. With quasiquotes
each one will create its own recipe, its own flavour and this is not good. I
would prefer something standard. The fact is that heterogeneous list are
powerful and flexible for doing unique things that are not possible with
other kind of structures, and the lack of standardization  (i.e sugaring to
begin with) makes them not being widely adopted.

That´s my opinion...

Albert.

2011/4/12 Antoine Latter <aslatter at gmail.com>

> On Tue, Apr 12, 2011 at 12:57 PM, Alberto G. Corona <agocorona at gmail.com>
> wrote:
> > Hi Cafe:
> > http://hackage.haskell.org/trac/ghc/ticket/1245
> >
> > I also want some kind of syntactic sugar for H. Lists.
> > The absence of syntactic sugar makes heterogeneous list to look scary.
> > People in haskell is accostumed to syntactic sugaring, so people think of
> > not sugared expressions as second class.
> > I´ don't know the details, but it seems that tuples are in the language
> to
> > cover the heterogeneous flexibility thing that homogeneous lists may not
> > provide, but they introduce its own inflexibilities; These repeating
> > instances for two, three, four and so on tuples makes them artificial and
> > repetitive. In its comparison, a complex but unique H. List instance look
> > elegant. specially if it is sugarized.
> > An alternative to sugarize H.Lists preserving tuples could be to use {}
> to
> > sugarize H. lists as
> >    {x,y,z}
> > and desugarize it into:
> > x :*: y :*: z :*: {}
> > Just like [] means empty list, {} would mean HNil, the empty
> heterogeneous
> > list.
> >
> > But this alternative , if implemented, would soon render tuples
>  obsolete.
> > These (,,) (,,,) constructors may create marginally faster and compact
> > structures, but they are much less manageable.
> >
>
> You could use quasi-quotes as an way to do this while you explore
> building it in to a compiler:
>
> > [hlist|5, "hello", True]
>
> You should be able to steal most of the implementation from
> haskell-src-exts-qq. It would work for expressions and patterns. You
> could even make a type quasi-quoter if you get ambitious.
>
> Antoine
>
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