On Apr 29, 2009, at 12:18 AM, Luke Palmer wrote:
On Tue, Apr 28, 2009 at 4:09 PM, Vasili I. Galchin <[email protected]
> wrote:
Hello,
Is there anyway when defining a dat type record struct to
indicate default values for some of the fields?
The usual pattern is to use a default record, and specialize it:
data Foo = Foo { bar :: Int, baz :: Int, quux :: Int }
fooDefault = Foo { bar = 1, baz = 2, quux = 3 }
newRecord = fooDefault { quux = 42 }
If you only want some of the fields to be defaulted, you can make
them undefined in the default record... unfortunately this won't be
checked by the compiler.
Luke
Additionally, you can choose to not export the constructor Foo and to
only export your fooDefault quasi-constructor and your record selectors.
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