Typescript nested type variables

Question

Have this:

type Format<A, R> = (arg: A) => R;

type FormatString<R> = (str: string) => R;

type FormatNumber<R> = (num: number) => R;

Would like to have this:

type Format<A<R>> = (arg: A) => R;

type FormatString = Format<string>;

type FormatNumber = Format<number>;

Or this:

type Format<A, R> = (arg: A) => R;

type FormatString = Format<string>;

type FormatNumber = Format<number>;

Currying or partial application for types is what I'm looking for. Or maybe some other workaround which keeps the code dry.

Without higher-kinded types this is not really possible without duplication. — jcalz
– jcalz, Commented Jul 31, 2018 at 17:10

Joseph Sikorski · Accepted Answer · 2018-07-31 17:06:45Z

3

Just add R as another type parameter on the partially specialized types.

type Format<A, R> = (arg: A) => R;

type FormatString<R> = Format<string, R>;

type FormatNumber<R> = Format<number, R>;

answered Jul 31, 2018 at 17:06

Joseph Sikorski

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