Difference between revisions of "Name clashes in record fields"
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(Duplicate record fields extension) |
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== See also == |
== See also == |
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− | * [http:// |
+ | * [http://prime.haskell.org/wiki/TypeDirectedNameResolution Type directed name resolution] |
* Haskell-Cafe on [http://www.haskell.org/pipermail/haskell-cafe/2010-December/087859.html Record types and unique names] |
* Haskell-Cafe on [http://www.haskell.org/pipermail/haskell-cafe/2010-December/087859.html Record types and unique names] |
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Revision as of 19:16, 4 April 2019
Question
error| Multiple declarations of ‘xxx’
I like to define:
data Human = Human {name :: String}
data Dog = Dog {name :: String}
Why is this forbidden?
I like to define:
data Human = Human {name :: String}
name :: Cat -> String
name = ...
Why is this forbidden, too?
Answer
The record field accessors name
are just functions
that retrieve the field's value from a particular record.
They are in the global scope together with top-level functions
and thus cannot have the same name.
For resolving this you may:
- rename the accessor or the top-level function
- put the data declaration or the top-level function in another module and import qualified
- write a typeclass with a
name
function and fit the non-accessor functionname
somehow into that.
Using language extension
DuplicateRecordFields
extension (GHC 8.0.1+) allow definition of record types with identically-named fields.
See also
- Type directed name resolution
- Haskell-Cafe on Record types and unique names