filter

If the Result is a Ok, passes its value to the predicate. If the predicate returns true, then the Result is returned unchanged. In every other case, an Error gets returned.

This feature is experimental!

This API is still experimental, so it may change or be removed in future versions. You should not rely on it for production applications.

Signature

Type(what is this?)

forall a: (Maybe a).((a) => Boolean) => Maybe a

Documentation

If the Result is a Ok, passes its value to the predicate. If the predicate returns true, then the Result is returned unchanged. In every other case, an Error gets returned.

Example:

const Result = require('folktale/result');

// This line evaluates to true.
Result.Ok.hasInstance(Result.Ok(3).filter(n => n === 3));

// These lines evaluate to false.
Result.Ok.hasInstance(Result.Ok(2).filter(n => n === 3));
Result.Ok.hasInstance(Result.Error(3).filter(n => n !== 3));
Result.Ok.hasInstance(Result.Error(3).filter(n => n === 3));

Properties

Source Code

Defined in source/result/result.js at line 75, column 19

{
    /*~*/
    Error: function filter(predicate) {
      assertFunction('Result.Error#filter', predicate);
      return this;
    },

    /*~*/
    Ok: function filter(predicate) {
      assertFunction('Result.Ok#filter', predicate);
      return predicate(this.value) ? this : Error();
    }
  }