Hi all, I wonder if there is some a "field of use" overlap between HList and functional references aka accessors. Do both tackle the same problem? Günther
I see them as addressing separate issues.
They overlap in that they both address the notion of how to access
attributes in some sense, but really they are complementary techniques.
HList as used by OOHaskell provides you with a mechanism by which you can
define extensible records and structural subtyping.
Functional references let you both read and write 'attributes' in a
structure. These can be chained to access members of members.
These techniques can be used together to get extensible records that have
settable fields in the form of functional references, where these references
can be chained together.
HList/OOHaskell doesn't concern itself with the 'deep reference' problem,
and functional references do not concern themselves directly with extensible
records.
-Edward Kmett
2010/2/2 Günther Schmidt
Hi all,
I wonder if there is some a "field of use" overlap between HList and functional references aka accessors.
Do both tackle the same problem?
Günther
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Hi, from all this I'm not so sure that these two techniques do not overlap. I mean HList tries to provide a technique for extensible Records, or composable data structures. So far it is possible in Haskell to extend / compose Data Structures but not at run-time and also rather clumsily. One could of course use tuples or rather nested pairs to compose data structures too, which would work at run-time. But that would be very hard to maintain. HList implements this composability by elaborate type-level programming. In my opinion functional references allows for this too but not through type-level programming. Am I wrong? Günther Am 04.02.10 13:18, schrieb Martijn van Steenbergen:
Edward Kmett wrote:
Functional references let you both read and write 'attributes' in a structure. These can be chained to access members of members.
You can also use them to build bidirectional views on fields (and compose those again as well).
Martijn.
participants (3)
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Edward Kmett -
Günther Schmidt -
Martijn van Steenbergen