Re: Proposal for containers: Add 'lookup' function to Data.Set

29 Jun 2016


      Let me be firm (co-maintainer's prerogative): the function will not be
named `lookup`. The current leader in my eyes is Andreas Abel's
`lookupEntry`, but I could be convinced to use something else if others
prefer
On Jun 29, 2016 5:12 PM, "Alec"  wrote:
...
...
Are there many cases where we want `lookup` where we don't actually
want `intern`?
Anecdotally, the majority of the times I've wanted `intern` functionality,
I've been implementing something full-text-search-like.  This meant having
a "load the lexicon" phase, where a set of blessed words get `intern`ed,
and then a query phase where I want is `lookup` because my lexicon is doing
double duty as a stoplist.  I have no sense of whether this would be a
common case.
Also, +1 for `intern`, +1 for `lookup`.  I'm fine with both names.
On Wed, Jun 29, 2016 at 4:57 PM David Thomas 
wrote:
...
Well, "intern" includes a "and if it is not there, add it".  Calling
this "intern" without that behavior would be highly misleading.  That
said, maybe we just want an "intern" function?  It would save us a dip
into the set, for new strings and leave (marginally) less room to make
a mistake.  Are there many cases where we want `lookup` where we don't
actually want `intern`?
...
Python uses "intern", so perhaps that can serve as the name.
(See https://docs.python.org/2/library/functions.html#intern)
On Tue, Jun 28, 2016 at 9:47 AM, David Feuer 
wrote:
...
+1 on the function. -1/2 on the name.
On Jun 27, 2016 5:45 PM, "Nicolas Godbout" 
wrote:
...
WHAT
It is proposed to add a ‘lookup' function on 'Set' in the "containers"
package. Feedback during the next two weeks is welcome.
The function
...
lookup :: Ord a => a -> Set a -> Maybe a
is almost indentical to the 'member' function but, in addition,
returns
...
the value
stored in the set.
WHY
The point of this proposal is to facilitate program-wide data
sharing. The
'lookup'
function gives access to a pointer to an object already stored in a
Set
and equal
to a given argument. The 'lookup' function is a natural extension to
...
...
...
current
'lookupLT', 'lookupGT', 'lookupLE' and 'lookupGE' functions, with
obvious
semantics.
Example use case: In a parser, the memory footprint can be reduced by
collapsing
all equal strings to a single instance of each string. To achieve
On Tue, Jun 28, 2016 at 2:22 AM, Chris Wong 
wrote:
the
this,
...
...
...
one needs
a way to get a previously seen string (internally, a pointer) equal
to a
newly
parsed string. Amazingly, this is very difficult with the current
"containers" library interface.
One current option is to use a Map instead, e.g., 'Map String String'
which stores twice as many pointers as necessary.
HOW
The git pull request at
https://github.com/haskell/containers/pull/291
contains the straight-forward implementation of the 'lookup’ function
on
'Set', with test cases,
as a patch against the current containers master branch.
Salutations,
Nicolas.
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--
Chris Wong (https://lambda.xyz)
"I had not the vaguest idea what this meant and when I could not
remember the words, my tutor threw the book at my head, which did not
stimulate my intellect in any way." -- Bertrand Russell
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