Re: [Haskell-cafe] [extension]syntactic sugar for maps

28 Mar 2013

      I agree that fromList or pattern matching at the function or case level are
readable. We probably don't need new sugar. For what it's worth, in scala
you can use "->" to construct tuples, so you'll sometimes see maps created
like this:

Map(1 -> "one", 2 -> "two", 3 -> "foo")

You can always do something similar in haskell (keeping in mind that "->"
is reserved):

import qualified Data.Map as Map

(-->) = (,)

makeMap = Map.fromList

myMap = makeMap [ 1 --> "one"
                , 2 --> "two"
                , 3 --> "foo"
                ]

Of course, it's not idiomatic and won't be immediately obvious to readers
that you are constructing tuples. However, if you find it easier to read
and need to write a lot of map literals in your code, it may be worth
coming up with a couple of aliases similar to those.

On Wed, Mar 27, 2013 at 1:16 PM, Eli Frey  wrote:
...
...
Sorry, I forgot to explain (probably because I'm too used to it). I am
referring to a syntax for easy creation of maps. Something equivalent to
lists:
to build a list: [ 1, 2, 3]
to build a map; { 1, "one", 2, "two", 3, "three"}
Without it I am always forced to use fromList.
This looks like something to use records for, or in any case something
where association list performance is not an issue.
If you just want to store some configuration-like structure and pass it
around, a record is great for this.  You might find where in other
languages you would simply leave a key "null", in Haskell you can just fill
it with a Nothing.
Maps (hash or binary-tree) really pay off when they are filled dynamically
with massive numbers of associations.  I find when I am ending up in this
scenario, I am generating my map programatically, not writing it as a
literal.
Sometimes people even write maps simply as functions and not even as a
data-structure.
...
myMap char = case char of
    'a' -> 1
    'b' -> 2
    'c' -> 3
Perhaps you could describe a situation you are in where you are wanting
this, and we could see if there is something you can do already that is
satisfying and solves your problem.
On Wed, Mar 27, 2013 at 12:59 PM, Eli Frey  wrote:
...
...
http://hackage.haskell.org/trac/ghc/wiki/OverloadedLists comes to mind.
This assumes you can turn ANY list into a thing.  Maps only make sense to
be constructed from association list.  If I've got a [Char], how do I make
a map form it?
On Wed, Mar 27, 2013 at 12:56 PM, Nicolas Trangez wrote:
...
On Wed, 2013-03-27 at 21:30 +0200, Răzvan Rotaru wrote:
...
I am terribly missing some syntactic sugar for maps (associative data
structures) in Haskell. I find myself using them more than any other
data
structure, and I think there is no big deal in adding some sugar for
this
to the language. I could not find out whether such an extension is
beeing
discussed. If not, I would like to propose and extension. Any help and
suggestions are very welcome here. Thanks.
http://hackage.haskell.org/trac/ghc/wiki/OverloadedLists comes to mind.
Nicolas
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Re: [Haskell-cafe] [extension]syntactic sugar for maps

Eric Rasmussen