How to create ADT in Haskell?What is the DataKinds extension of Haskell?Getting started with HaskellIs the Scala 2.8 collections library a case of “the longest suicide note in history”?Large-scale design in Haskell?Memory footprint of Haskell data typesSpeed comparison with Project Euler: C vs Python vs Erlang vs HaskellWhat is a sealed trait?“Composite” algebraic data types in Scala and HaskellGetting associated type synonyms with template HaskellHaskell nested algebraic data typewhat makes a class/trait in scala an ADT
Is a model fitted to data or is data fitted to a model?
Is possible to search in vim history?
What's the difference between 違法 and 不法?
Reply 'no position' while the job posting is still there
Divine apple island
Do Legal Documents Require Signing In Standard Pen Colors?
Can we have a perfect cadence in a minor key?
Did arcade monitors have same pixel aspect ratio as TV sets?
Why has "pence" been used in this sentence, not "pences"?
Are lightweight LN wallets vulnerable to transaction withholding?
Has Darkwing Duck ever met Scrooge McDuck?
About a little hole in Z'ha'dum
Why did the HMS Bounty go back to a time when whales are already rare?
What is this type of notehead called?
What does this horizontal bar at the first measure mean?
Visiting the UK as unmarried couple
Bob has never been a M before
Do the concepts of IP address and network interface not belong to the same layer?
Why does Async/Await work properly when the loop is inside the async function and not the other way around?
THT: What is a squared annular “ring”?
How to decide convergence of Integrals
Could solar power be utilized and substitute coal in the 19th Century
Query about absorption line spectra
What linear sensor for a keyboard?
How to create ADT in Haskell?
What is the DataKinds extension of Haskell?Getting started with HaskellIs the Scala 2.8 collections library a case of “the longest suicide note in history”?Large-scale design in Haskell?Memory footprint of Haskell data typesSpeed comparison with Project Euler: C vs Python vs Erlang vs HaskellWhat is a sealed trait?“Composite” algebraic data types in Scala and HaskellGetting associated type synonyms with template HaskellHaskell nested algebraic data typewhat makes a class/trait in scala an ADT
In Scala I can describe such ADT:
sealed trait Foo
case class A(a: Int) extends Foo
case class B(b: String) extends Foo
case class C(a: A, b: B) extends Foo
How can I do the same in Haskell?
data Foo = A Int | B String | C A B
It doesn't work, because A and B are not types. Should I use GHC extensions to do it?
scala haskell algebraic-data-types
New contributor
add a comment |
In Scala I can describe such ADT:
sealed trait Foo
case class A(a: Int) extends Foo
case class B(b: String) extends Foo
case class C(a: A, b: B) extends Foo
How can I do the same in Haskell?
data Foo = A Int | B String | C A B
It doesn't work, because A and B are not types. Should I use GHC extensions to do it?
scala haskell algebraic-data-types
New contributor
add a comment |
In Scala I can describe such ADT:
sealed trait Foo
case class A(a: Int) extends Foo
case class B(b: String) extends Foo
case class C(a: A, b: B) extends Foo
How can I do the same in Haskell?
data Foo = A Int | B String | C A B
It doesn't work, because A and B are not types. Should I use GHC extensions to do it?
scala haskell algebraic-data-types
New contributor
In Scala I can describe such ADT:
sealed trait Foo
case class A(a: Int) extends Foo
case class B(b: String) extends Foo
case class C(a: A, b: B) extends Foo
How can I do the same in Haskell?
data Foo = A Int | B String | C A B
It doesn't work, because A and B are not types. Should I use GHC extensions to do it?
scala haskell algebraic-data-types
scala haskell algebraic-data-types
New contributor
New contributor
edited yesterday
mfirry
2,75811729
2,75811729
New contributor
asked yesterday
AndrewAndrew
834
834
New contributor
New contributor
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
In Scala, your ADT makes A
,B
,C
to be subtypes of Foo
. In Haskell we do not have subtypes, so A
,B
,C
are instead constructors of type Foo
.
A few possible workarounds:
Repeat the fields. This is the most basic option.
data Foo = A Int | B String | C Int String
Define additional types, so that we can reuse them more than once.
data AT = AT Int -- can have many arguments
data BT = BT String -- can have many arguments
data Foo = A AT | B BT | C AT BTExploit a GADT
data FooTag = AT | BT | CT
data Foo (tag :: FooTag) where
A :: Int -> Foo 'AT
B :: String -> Foo 'BT
C :: Foo 'AT -> Foo 'BT -> Foo 'CTHere, in the last line we are able to refer to "the values constructed using
A
" using the typeFoo 'AT
, since tagAT
is only used by constructorA
.
Note that this approach adds a tag parameter toFoo
, so it slightly changes the interface: we can no longer writebar :: Foo -> ...
, but we have to writebar :: Foo t -> ...
(or to use existential types).
4
The last example requires several extensions, though, right? (DataKinds
,GADTs
, andKindSignatures
, I think.)
– chepner
yesterday
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Andrew is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55311975%2fhow-to-create-adt-in-haskell%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
In Scala, your ADT makes A
,B
,C
to be subtypes of Foo
. In Haskell we do not have subtypes, so A
,B
,C
are instead constructors of type Foo
.
A few possible workarounds:
Repeat the fields. This is the most basic option.
data Foo = A Int | B String | C Int String
Define additional types, so that we can reuse them more than once.
data AT = AT Int -- can have many arguments
data BT = BT String -- can have many arguments
data Foo = A AT | B BT | C AT BTExploit a GADT
data FooTag = AT | BT | CT
data Foo (tag :: FooTag) where
A :: Int -> Foo 'AT
B :: String -> Foo 'BT
C :: Foo 'AT -> Foo 'BT -> Foo 'CTHere, in the last line we are able to refer to "the values constructed using
A
" using the typeFoo 'AT
, since tagAT
is only used by constructorA
.
Note that this approach adds a tag parameter toFoo
, so it slightly changes the interface: we can no longer writebar :: Foo -> ...
, but we have to writebar :: Foo t -> ...
(or to use existential types).
4
The last example requires several extensions, though, right? (DataKinds
,GADTs
, andKindSignatures
, I think.)
– chepner
yesterday
add a comment |
In Scala, your ADT makes A
,B
,C
to be subtypes of Foo
. In Haskell we do not have subtypes, so A
,B
,C
are instead constructors of type Foo
.
A few possible workarounds:
Repeat the fields. This is the most basic option.
data Foo = A Int | B String | C Int String
Define additional types, so that we can reuse them more than once.
data AT = AT Int -- can have many arguments
data BT = BT String -- can have many arguments
data Foo = A AT | B BT | C AT BTExploit a GADT
data FooTag = AT | BT | CT
data Foo (tag :: FooTag) where
A :: Int -> Foo 'AT
B :: String -> Foo 'BT
C :: Foo 'AT -> Foo 'BT -> Foo 'CTHere, in the last line we are able to refer to "the values constructed using
A
" using the typeFoo 'AT
, since tagAT
is only used by constructorA
.
Note that this approach adds a tag parameter toFoo
, so it slightly changes the interface: we can no longer writebar :: Foo -> ...
, but we have to writebar :: Foo t -> ...
(or to use existential types).
4
The last example requires several extensions, though, right? (DataKinds
,GADTs
, andKindSignatures
, I think.)
– chepner
yesterday
add a comment |
In Scala, your ADT makes A
,B
,C
to be subtypes of Foo
. In Haskell we do not have subtypes, so A
,B
,C
are instead constructors of type Foo
.
A few possible workarounds:
Repeat the fields. This is the most basic option.
data Foo = A Int | B String | C Int String
Define additional types, so that we can reuse them more than once.
data AT = AT Int -- can have many arguments
data BT = BT String -- can have many arguments
data Foo = A AT | B BT | C AT BTExploit a GADT
data FooTag = AT | BT | CT
data Foo (tag :: FooTag) where
A :: Int -> Foo 'AT
B :: String -> Foo 'BT
C :: Foo 'AT -> Foo 'BT -> Foo 'CTHere, in the last line we are able to refer to "the values constructed using
A
" using the typeFoo 'AT
, since tagAT
is only used by constructorA
.
Note that this approach adds a tag parameter toFoo
, so it slightly changes the interface: we can no longer writebar :: Foo -> ...
, but we have to writebar :: Foo t -> ...
(or to use existential types).
In Scala, your ADT makes A
,B
,C
to be subtypes of Foo
. In Haskell we do not have subtypes, so A
,B
,C
are instead constructors of type Foo
.
A few possible workarounds:
Repeat the fields. This is the most basic option.
data Foo = A Int | B String | C Int String
Define additional types, so that we can reuse them more than once.
data AT = AT Int -- can have many arguments
data BT = BT String -- can have many arguments
data Foo = A AT | B BT | C AT BTExploit a GADT
data FooTag = AT | BT | CT
data Foo (tag :: FooTag) where
A :: Int -> Foo 'AT
B :: String -> Foo 'BT
C :: Foo 'AT -> Foo 'BT -> Foo 'CTHere, in the last line we are able to refer to "the values constructed using
A
" using the typeFoo 'AT
, since tagAT
is only used by constructorA
.
Note that this approach adds a tag parameter toFoo
, so it slightly changes the interface: we can no longer writebar :: Foo -> ...
, but we have to writebar :: Foo t -> ...
(or to use existential types).
edited yesterday
answered yesterday
chichi
76.8k287145
76.8k287145
4
The last example requires several extensions, though, right? (DataKinds
,GADTs
, andKindSignatures
, I think.)
– chepner
yesterday
add a comment |
4
The last example requires several extensions, though, right? (DataKinds
,GADTs
, andKindSignatures
, I think.)
– chepner
yesterday
4
4
The last example requires several extensions, though, right? (
DataKinds
, GADTs
, and KindSignatures
, I think.)– chepner
yesterday
The last example requires several extensions, though, right? (
DataKinds
, GADTs
, and KindSignatures
, I think.)– chepner
yesterday
add a comment |
Andrew is a new contributor. Be nice, and check out our Code of Conduct.
Andrew is a new contributor. Be nice, and check out our Code of Conduct.
Andrew is a new contributor. Be nice, and check out our Code of Conduct.
Andrew is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55311975%2fhow-to-create-adt-in-haskell%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown