TypeScript Declaration File (.d.ts) generator for PureScript
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README.md

purescript-tsd-gen

This is a TypeScript Declaration File (.d.ts) generator for PureScript.

This tool helps you use PureScript modules from TypeScript.

How to build

$ git clone https://github.com/minoki/purescript-tsd-gen.git
$ cd purescript-tsd-gen
$ stack install

How to use

Assuming you have compiled PureScript modules into ./output:

$ tree output/
output/
├── Control.Alt
│   ├── externs.json
│   └── index.js
├── Control.Alternative
│   ├── externs.json
│   └── index.js
...
└── YourFancyModuleInPurs
    ├── externs.json
    └── index.js

Run the following to get the declaration files:

$ purs-tsd-gen -d output/ YourFancyModuleInPurs

Now you get index.d.ts alongside each module's index.js:

$ tree output/
output/
├── Control.Alt
│   ├── externs.json
│   ├── index.d.ts
│   └── index.js
├── Control.Alternative
│   ├── externs.json
│   ├── index.d.ts
│   └── index.js
...
└── YourFancyModuleInPurs
    ├── externs.json
    ├── index.d.ts
    └── index.js

Mapping of types

Builtin

Primitive types translates as one would imagine:

  • Function s t (s -> t) --> (_: s) => t
  • Array t --> Array<t>
    • TODO: Add an option to emit ReadonlyArray<t>.
  • Record { key1 :: Type1, key2 :: Type2 } --> { key1: Type1, key2: Type2 }
    • TODO: Add an option to make fields readonly.
  • Number, Int --> number
  • String, Char --> string
  • Boolean --> boolean

Some modules get special handling:

  • Data.Function.Uncurried
    • Fn0 r --> () => r
    • Fn2 a0 a1 r --> (_0: a0, _1: a2) => r
    • Fn3 a0 a1 a2 r --> (_0: a0, _1: a1, _2: a2) => r
    • ...
    • Fn10 a0 a1 .. a9 r --> (_0: a0, ..., _9: a9) => r
  • Effect
    • Effect a -> () => a
  • Control.Monad.Eff
    • Eff e r -> () => r
  • Data.StrMap.StrMap
    • StrMap t --> {[_: string]: t}
  • Data.Variant (from purescript-variant)
    • Variant (tag1 :: Type1, tag2 :: Type2) --> {type: "tag1", value: Type1} | {type: "tag2", value: Type2}
  • Data.Nullable (from purescript-nullable)
    • Nullable a --> a | null

User-defined Data Types

Data type SomeFancyDataType :: Type -> ... -> Type -> Type is translated to SomeFancyDataType<a0, ..., an>.

In contrast to usual TypeScript's structual subtyping, the translated types mimicks nominal typing with extra dummy fields.

Sum types are translated to discriminated union types, with a dummy tag field. Type guards with instanceof should work.

Data constructors are typed as an object type with new signature and create or value field.

Types whose data constructors are not exposed, i.e. abstract types, are translated to an object type which contains never as a field, so that you cannot accidentally create a value of abstract types in TypeScript world.

Let's see some examples:

  • Tuple
data Tuple a b = Tuple a b

compiles to:

export type /*data*/ Tuple<a, b> = Tuple$$Tuple< a, b >;
interface Tuple$$Tuple<a, b> {
    "$$pursType"?: "Data.Tuple.Tuple";
    "$$pursTag"?: "Tuple";
    value0: a;
    value1: b;
}
export const /*data ctor*/ Tuple: { create: <a, b>(_: a) => (_: b) => Tuple< a, b >; new <a, b>(_0: a, _1: b): Tuple$$Tuple< a, b > };
  • Maybe
data Maybe a = Nothing | Just a

compiles to:

export type /*data*/ Maybe<a> = Maybe$$Nothing | Maybe$$Just< a >;
interface Maybe$$Nothing {
    "$$pursType": "Data.Maybe.Maybe";
    "$$pursTag": "Nothing";
}
export const /*data ctor*/ Nothing: { value: Maybe< any /* type variable a */ >; new (): Maybe$$Nothing };
interface Maybe$$Just<a> {
    "$$pursType": "Data.Maybe.Maybe";
    "$$pursTag": "Just";
    value0: a;
}
export const /*data ctor*/ Just: { create: <a>(_: a) => Maybe< a >; new <a>(_: a): Maybe$$Just< a > };
  • Either
data Either a b = Left a | Right b

compiles to:

export type /*data*/ Either<a, b> = Either$$Left< a > | Either$$Right< b >;
interface Either$$Left<a> {
    "$$pursType": "Data.Either.Either";
    "$$pursTag": "Left";
    value0: a;
}
export const /*data ctor*/ Left: { create: <a, b>(_: a) => Either< a, b >; new <a>(_: a): Either$$Left< a > };
interface Either$$Right<b> {
    "$$pursType": "Data.Either.Either";
    "$$pursTag": "Right";
    value0: b;
}
export const /*data ctor*/ Right: { create: <a, b>(_: b) => Either< a, b >; new <b>(_: b): Either$$Right< b > };

Newtypes

Newtypes are translated to a type synonym. The nominal property in PureScript is lost.

foreign import data

foreign import data are translated to any.

Maybe there should be a way for PS-library authors to provide corresponding .d.ts for foreign JavaScript modules.

Universally Quantified Types

Simple polymorphic functions translate to generic functions.

If the type is too complex, there may situations where the emitted declarations contain undue any type.

Higher-Kinded Types

Not supported.

TODO: Investigate if we can reasonably emulate higher-kinded types in TypeScript.

Type Classes

Need more work.