[Haskell-cafe] syntactic sugar for heterogeneous lists

[Alberto G. Corona]

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.
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