[Haskell-cafe] Embedded Functions in Algebraic Data Types?
On a lark, I loaded this into Hugs this morning, and it didn't complain: data Thing = Thing (Integer - Integer) But, I've never seen that sort of construct in an example. Do people ever embed functions in ADTs? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
2008/2/10, Michael Feathers [EMAIL PROTECTED]: On a lark, I loaded this into Hugs this morning, and it didn't complain: data Thing = Thing (Integer - Integer) But, I've never seen that sort of construct in an example. Do people ever embed functions in ADTs? Yes, anyway you can embed function in Maybe a or Either a b for example, since they're polymorphic. Embedding functions in ADT purposefully happens quite often too, just look at the State Monad, the functionnal references proposal and so on... Recently I embedded functions into a denotational semantic ADT for a tiny DSL, there's plenty of use cases. -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
On Feb 10, 2008 1:34 PM, Michael Feathers [EMAIL PROTECTED] wrote: On a lark, I loaded this into Hugs this morning, and it didn't complain: data Thing = Thing (Integer - Integer) But, I've never seen that sort of construct in an example. Do people ever embed functions in ADTs? Yes, this is quite common. Here's a quick example (untested): data MyMap key value = M (key - Maybe value) lookup (M m) key = m key insert (M m) key value = M (\key' - if key' == key then Just value else m key') This is a naive data structure for storing a map as a function from the key to the value. Not very efficient, perhaps, but you use similar concepts in more useful scenarios (e.g. the State monad). -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
Quite frequently.
Here are a few examples from my own code:
For functional references (representing a bidirectional function
from a data type to a part of itself (for example the first element of
a pair)).
data Accessor s a
= Accessor { get :: s - a
, set :: a - s - s
}
My quantum computation arrow (really in the realm of concrete, useful
things, huh? :-)
data Operator b c
= Op (forall d. QStateVec (b,d) - IO (QStateVec (c,d)))
| ...
The ubiquitous FRP Behavior, comprising a current value and a function
which takes a timestep and returns the next value.
data Behavior a
= Behavior a (Double - Behavior a)
The suspend monad, representing a computation which can either
finish now with a value of type a, or suspends to request a value of
type v before continuing.
data Suspend v a
= Return a
| Suspend (v - Suspend v a)
It seems that most frequently, functions in ADTs are used when
implementing monads or arrows, but that doens't need to be the case.
A lot of times a function is the best way to represent a particular
part of a data structure :-)
Luke
On Feb 10, 2008 1:34 PM, Michael Feathers [EMAIL PROTECTED] wrote:
On a lark, I loaded this into Hugs this morning, and it didn't complain:
data Thing = Thing (Integer - Integer)
But, I've never seen that sort of construct in an example. Do people
ever embed functions in ADTs?
Michael
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Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
On Feb 10, 2008 1:42 PM, Sebastian Sylvan [EMAIL PROTECTED] wrote: On Feb 10, 2008 1:34 PM, Michael Feathers [EMAIL PROTECTED] wrote: On a lark, I loaded this into Hugs this morning, and it didn't complain: data Thing = Thing (Integer - Integer) But, I've never seen that sort of construct in an example. Do people ever embed functions in ADTs? Yes, this is quite common. Here's a quick example (untested): data MyMap key value = M (key - Maybe value) lookup (M m) key = m key insert (M m) key value = M (\key' - if key' == key then Just value else m key') This is a naive data structure for storing a map as a function from the key to the value. Not very efficient, perhaps, but you use similar concepts in more useful scenarios (e.g. the State monad). Perhaps I should add an empty MyMap too: empty = M (\_- Nothing ) -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
Great. Thanks to everyone!
Michael
Luke Palmer wrote:
Quite frequently.
Here are a few examples from my own code:
For functional references (representing a bidirectional function
from a data type to a part of itself (for example the first element of
a pair)).
data Accessor s a
= Accessor { get :: s - a
, set :: a - s - s
}
My quantum computation arrow (really in the realm of concrete, useful
things, huh? :-)
data Operator b c
= Op (forall d. QStateVec (b,d) - IO (QStateVec (c,d)))
| ...
The ubiquitous FRP Behavior, comprising a current value and a function
which takes a timestep and returns the next value.
data Behavior a
= Behavior a (Double - Behavior a)
The suspend monad, representing a computation which can either
finish now with a value of type a, or suspends to request a value of
type v before continuing.
data Suspend v a
= Return a
| Suspend (v - Suspend v a)
It seems that most frequently, functions in ADTs are used when
implementing monads or arrows, but that doens't need to be the case.
A lot of times a function is the best way to represent a particular
part of a data structure :-)
Luke
On Feb 10, 2008 1:34 PM, Michael Feathers [EMAIL PROTECTED] wrote:
On a lark, I loaded this into Hugs this morning, and it didn't complain:
data Thing = Thing (Integer - Integer)
But, I've never seen that sort of construct in an example. Do people
ever embed functions in ADTs?
Michael
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Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
On Sun, 10 Feb 2008, Henning Thielemann wrote:
On Sun, 10 Feb 2008, Luke Palmer wrote:
Quite frequently.
Here are a few examples from my own code:
For functional references (representing a bidirectional function
from a data type to a part of itself (for example the first element of
a pair)).
data Accessor s a
= Accessor { get :: s - a
, set :: a - s - s
}
My quantum computation arrow (really in the realm of concrete, useful
things, huh? :-)
The pattern seems to be common enough to be turned into a package.
http://www.haskell.org/haskellwiki/?title=Record_accessaction=history
I meant
http://www.haskell.org/haskellwiki/Record_access
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Re: [Haskell-cafe] Embedded Functions in Algebraic Data Types?
On Sun, 10 Feb 2008, Luke Palmer wrote:
Quite frequently.
Here are a few examples from my own code:
For functional references (representing a bidirectional function
from a data type to a part of itself (for example the first element of
a pair)).
data Accessor s a
= Accessor { get :: s - a
, set :: a - s - s
}
My quantum computation arrow (really in the realm of concrete, useful
things, huh? :-)
The pattern seems to be common enough to be turned into a package.
http://www.haskell.org/haskellwiki/?title=Record_accessaction=history
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