Record Systems Dylan Just YOW LambdaJam 2015 Haskell Elm - - PowerPoint PPT Presentation

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Record Systems Dylan Just YOW LambdaJam 2015 Haskell Elm - - PowerPoint PPT Presentation

Aug 10, 2023 228 likes •1.4k views

Record Systems Dylan Just YOW LambdaJam 2015 Haskell Elm PureScript OCaml Idris Pascal Haskell Java classes Elm Scala classes PureScript C structs OCaml Database tables Idris Pascal Haskell Elm PureScript Haskell Elm

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Record Systems

Dylan Just YOW LambdaJam 2015

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Haskell Elm PureScript OCaml Idris Pascal

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Haskell Elm PureScript OCaml Idris Pascal Java classes Scala classes C structs Database tables

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Haskell Elm PureScript

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Haskell Elm PureScript Vinyl

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Haskell Elm PureScript Vinyl

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What are records? What can they do?

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Structural typing Row polymorphism

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What is a record?

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Set of fields with

  • name
  • type
  • value

Record =

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Set of fields with

  • name
  • type
  • value

Record =

type-level information value-level information

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Set of fields with

  • name
  • type
  • value

Record =

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Basic Operations

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Declare Type

data Person = Person {name::String, age::Int}

haskell

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Instantiate

data Person = Person {name::String, age::Int} bob = Person {name="Bob", age=30}

haskell

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Get

data Person = Person {name::String, age::Int} bob = Person {name="Bob", age=30} bobName = name bob

haskell

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Set

data Person = Person {name::String, age::Int} bob = Person {name="Bob", age=30} bobName = name bob

  • lderBob = bob {age=31}

haskell

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Haskell Problems

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Namespacing

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data Pos2D = Pos2D {x::Int, y::Int} data Pos3D = Pos3D {x::Int, y::Int, z::Int}

haskell

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data Pos2D = Pos2D {x::Int, y::Int} data Pos3D = Pos3D {x::Int, y::Int, z::Int}

haskell

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data Pos2D = Pos2D {x::Int, y::Int} data Pos3D = Pos3D {x::Int, y::Int, z::Int}

Compile error

haskell

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Namespacing.hs:2:22: Multiple declarations of ‘x’ Declared at: Namespacing.hs:1:22 Namespacing.hs:2:22 Namespacing.hs:2:32: Multiple declarations of ‘y’ Declared at: Namespacing.hs:1:32 Namespacing.hs:2:32

haskell

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Overlapping Record Names

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data Key = StringKey { key :: String } | NumericKey { key :: Int }

haskell

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data Key = StringKey { key :: String } | NumericKey { key :: Int }

Compile error

haskell

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Constructors StringKey and NumericKey give different types for field ‘key’ In the data declaration for ‘Key’

haskell

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Partial Accessors

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int}

haskell

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4}

haskell

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4} r_radius = case r of (Circle {radius=r}) -> r (Rectangle {}) -> -1 > r_radius

  • 1

haskell

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4} r_radius = radius r > r_radius' *** Exception: No match in record selector radius

Run-time error

haskell

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Haskell vs PureScript

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Namespacing

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data Pos2D = Pos2D {x::Int, y::Int} data Pos3D = Pos3D {x::Int, y::Int, z::Int}

Compile error

haskell

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data Pos2D = Pos2D {x::Number,y::Number} data Pos3D = Pos3D {x::Number,y::Number,z::Number}

purescript

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Overlapping Record Names

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data Key = StringKey { key :: String } | NumericKey { key :: Int }

Compile error

haskell

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data Key = StringKey { key :: String } | NumericKey { key :: Number }

purescript

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Partial Accessors

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4} r_radius = radius r > r_radius' *** Exception: No match in record selector radius

Run-time error

haskell

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4} r_radius = case r of (Circle {radius=rad}) -> rad (Rectangle {}) -> -1 > r_radius

  • 1

haskell

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data Shape = Circle {radius::Number} | Rectangle {width::Number, height::Number} r = Rectangle {width:3, height:4} r_radius = case r of (Circle {radius=rad}) -> rad (Rectangle {}) -> -1 > r_radius

  • 1

purescript

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} r = Rectangle {width=3, height=4} r_radius = case r of (Circle r') -> r' (Rectangle w' h') -> -1 > r_radius

  • 1

haskell

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data Shape = Circle {radius::Number} | Rectangle {width::Number, height::Number} r = Rectangle {width:3, height:4} r_radius = case r of (Circle c') -> c'.radius (Rectangle r') -> -1 > r_radius

  • 1

purescript

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r_radius = case r of (Circle r') -> r' (Rectangle w' h') -> -1 r_radius = case r of (Circle c') -> c'.radius (Rectangle r') -> -1

purescript haskell

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data Shape = Circle {radius::Int} | Rectangle {width::Int, height::Int} c = Circle {radius=3} c' = Circle 3

haskell

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data Shape = Circle { radius::Int } | Rectangle { width::Int, height::Int }

Fields are constructor parameters

haskell

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data Shape = Circle { radius::Number } | Rectangle { width::Number, height::Number }

Records are constructor parameters

purescript

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data X = X { a :: String }

purescript

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data X = X { a :: String } data Y = Y String {a :: String}

purescript

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data X = X { a :: String } data Y = Y String {a :: String} data Z = Z {a::String,b::Number} Number {c::String}

purescript

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data X = X { a :: String } data Y = Y String {a :: String} data Z = Z {a::String,b::Number} Number {c::String} type Q = {a::String, b::Int}

purescript

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data X = X { a :: String } data Y = Y String {a :: String} data Z = Z {a::String,b::Number} Number {c::String} type Q = {a::String, b::Int} Tagged Untagged

purescript

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Tagged vs Untagged

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Tagged data Pos2D = Pos2D {x::Number,y::Number} p = Pos2D {x:3,y:4} Untagged type Pos2D = {x::Number,y::Number} p = {x:3,y:4}

purescript

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Nominal Type data Pos2D = Pos2D {x::Number,y::Number} p = Pos2D {x:3,y:4} Structural Type type Pos2D = {x::Number,y::Number} p = {x:3,y:4}

purescript

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Nominal Typing Two values are type-compatible iff their declarations name the same type.

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Structural Typing Two values are type-compatible iff they exhibit the same structure.

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Structural Typing

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Extensible Records Row Polymorphism Record Subtyping

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Extensible Records Row Polymorphism Record Subtyping

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Extensible Records

  • add fields
  • remove fields
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PureScript Elm

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Create > bob = {name="bob"} {name="bob"} : {name:String}

elm

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Add Field > bob = {name="bob"} {name="bob"} : {name:String} > bob' = {bob | age=33} {name="bob",age=33} : {name:String,age:number}

elm

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Remove Field > bob = {name="bob"} {name="bob"} : {name:String} > bob' = {bob | age=33} {name="bob",age=33} : {name:String,age:number} > bob'' = {bob' - age} {name="bob"} : {name:String}

elm

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Row Polymorphism

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Back to PureScript...

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type House = {color::String,rooms::Number} type Car = {color::String,model::String}

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse :: House myhouse = {color:"pink",rooms:3} mycar :: Car mycar = {color:"red",model:"Corolla"}

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"}

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} getColor :: House -> String getColor x = x.color getColor' :: Car -> String getColor' x = x.color

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} getColor :: forall r. {color::String | r} -> String getColor x = x.color

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} getColor :: forall r. {color::String | r} -> String getColor x = x.color > getColor myhouse "pink"

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} getColor :: forall r. {color::String | r} -> String getColor x = x.color > getColor mycar "red"

purescript

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getColor :: forall r. {color::String | r} -> String

Any other fields Required fields

purescript

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getColor :: forall r. {color::String | r} -> String

Polymorphic Row Variable Required fields

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} getColor :: forall r. {color::String | r} -> String getColor x = x.color

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} lighten::forall r.{color::String|r} -> {color::String|r} lighten x = x { color = "light " ++ x.color }

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} lighten::forall r.{color::String|r} -> {color::String|r} lighten x = x { color = "light " ++ x.color } > getColor (lighten myhouse) "light pink"

purescript

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type House = {color::String,rooms::Number} type Car = {color::String,model::String} myhouse = {color:"pink",rooms:3} mycar = {color:"red",model:"Corolla"} lighten::forall r.{color::String|r} -> {color::String|r} lighten x = x { color = "light " ++ x.color } > getColor (lighten mycar) "light red"

purescript

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Haskell strikes back!

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Type-level Strings

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data Person = Person {firstName::String, lastName::String} bob :: Person bob = Person {firstName="bob", lastName="cuttey"} bobFirstName = firstName bob bobLastName = lastName bob

haskell

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type Person = Map String String bob' :: Person bob' = fromList [("firstName", "bob"), ("lastName", "cuttey")] bobFirstName' = bob' ! "firstName" bobLastName' = bob' ! "lastName"

haskell

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bob = Person {firstName="bob", lastName="cuttey"} bob' = fromList [("firstName", "bob"), ("lastName", "cuttey")]

haskell

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bob = Person {firstName="bob", lastName="cuttey"} bob' = fromList [("firstName", "bob"), ("lastName", "cuttey")]

String Field name

haskell

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bob = Person {firstName="bob", lastName="cuttey"} bob' = fromList [("firstName", "bob"), ("lastName", "cuttey")]

Value-level information Type-level information

haskell

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Kind Type Value

type of type of haskell

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Kind * Type String Value "hello"

haskell

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Kind * Symbol Type String "firstName" Value "hello"

  • haskell
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Kind * Symbol Type String "firstName" Value "hello"

  • Value-level String

Type-level String

haskell

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data Field (fieldName::Symbol) a = Field a bob :: Field "firstName" String bob = Field "bob"

haskell

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data Field (fieldName::Symbol) a = Field a bob :: Field "firstName" String bob = Field "bob" name type value

haskell

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Vinyl

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{-# LANGUAGE DataKinds, KindSignatures TypeOperators, GADTs, MultiParamTypeClasses #-} import Data.Vinyl get key rec = getField (rget key rec)

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String)

SField Constructor SField Type Constructor

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String)

Field Name Field Type

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String)

Pair type

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String)

Type-level String Type Pair type

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey"

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey"

Create record with 1 field

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey"

Append records

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey" bobFirstName = get firstName bob bobLastName = get lastName bob

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey" bobFirstName = get firstName bob bobLastName = get lastName bob dog = firstName =: "doggie" dogFirstName = get firstName dog

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey" bobFirstName = get firstName bob bobLastName = get lastName bob dog = firstName =: "doggie" dogFirstName = get firstName dog

haskell

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firstName = SField :: SField '("firstName", String) lastName = SField :: SField '("lastName", String) bob = firstName =: "bob" <+> lastName =: "cuttey" bobFirstName = get firstName bob bobLastName = get lastName bob dog = firstName =: "doggie" dogFirstName = get firstName dog

Row polymorphism!

haskell

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In conclusion...

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Record = {(Name, Type, Value)}

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Define record type Instantiate type Get field Set field Add field Remove field

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Structural typing

  • Extensible records
  • Row Polymorphism
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Built-in record systems: Elm > PureScript > Haskell

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Vinyl library

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Cheers!

Slides and code at https://github.com/techtangents/recordsystemstalk