Re: [Haskell-cafe] record update

On Sat, 11 Sep 2010, Stephen Tetley wrote:

On 11 September 2010 18:21, Jonathan Geddes wrote:

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someUpdate :: MyRecord -> MyRecord someUpdate myRecord = myRecord     { field1 = f $ field1 myRecord     , field2 = g $ field2 myRecord     , field3 = h $ filed3 myRecord     }

Applicatively, using no additional libraries, is how I do it:

updateAllThree :: MyRecord -> MyRecord updateAllThree = (\s a b c -> s { field1 = f a, field2 = g b, field3 = h c}) <*> field1 <*> field2 <*> field3

Cute!

Note - (<$>) is not used, and the left hand function has one extra argument. This style exploits the fact that (<*>) is the Startling (S) combinator.

It uses the Applicative instance for functions.