Comment by phpnode | Hacker News Reader

Comment by phpnode | Hacker News Reader

It would be nice to be able to use the annotations directly, we support this in flow-runtime[0] but I think it would be fairly straightforward to support in TypeScript too,

It looks like this:

    import t from 'flow-runtime';

    const makeUpperCase = t.pattern(
      (input: string) => input.toUpperCase(),
      (input: number) => input
    );

    console.log(makeUpperCase("foo bar"));
    console.log(makeUpperCase(123));
    console.log(makeUpperCase(false)); // throws

[0] https://codemix.github.io/flow-runtime/#/docs/pattern-matchi...

Shouldn't the uppercase of a number be a string?

    const makeUpperCase = t.pattern(
      (input: string) => input.toUpperCase(),
      (input: number) => '' + input
    );

Otherwise you get odd behaviours like:

    makeUpperCase('1') + makeUpperCase('1') = '11' (probably what you want)
    makeUpperCase(1) + makeUpperCase(1) = 2 (probably not what you want)

Yeah probably, but it's just an example

...wait. Why would the uppercase of '1' be '11'? It would just be '1'.

I had to reread it a few times to parse it. Its result of "adding" the uppercase of 1 that should be 11, not the uppercase itself.

In other words, the result of "makeUppercase" should be a string, not a number.

I see it now.

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