Syntax Lookup

Enter some language construct you want to know more about.
This is a scoped polymorphic type.

In ReScript, polymorphic functions can only deal with one specific type. When they are called, their type gets fixed. For instance this logging function is bound in a polymorphic way as you can see by the type parameter ('a).

RES
type logger<'a> = { log: 'a => unit}

@module("jsAPI") external getLogger: unit => logger<'a> = "getLogger"

let myLogger = getLogger()

myLogger.log("Hello, ReScript!")
myLogger.log(42) // Type error!

Scoped polymorphic types make such behavior possible, in a type-safe way. See the 'a. in the example below.

Example

ReScriptJS Output
type logger = { log: 'a. 'a => unit}

@module("jsAPI") external getLogger: unit => logger = "getLogger"

let myLogger = getLogger()

myLogger.log("Hello, ReScript!")
myLogger.log(42) // Ok!

References