Assume I have such code:
function concat(a: string, b: string):string {
return a + b;
}
function firstPlusWorld(items: string[]):string {
return concat(items[0], ' World');
}
console.log(firstPlusWorld([]));
In this case typescript won't argue that the first argument passed to concat is not a string.
In functional land there is Maybe type and head function has type signature
head :: List a -> Maybe a
Is there any way to make typescript handle such cases?
Unfortunately, you will have to resort to good/old if tests. Typescript does not add anything to javascript in that respect.
There are tentatives to bring Monads to Javascript (and Typescript by extension) such as this one: https://github.com/fantasyland/fantasy-land (https://github.com/fantasyland for implementations)
I am still frustrated at this stage and if anyone finds a good library, I will be glad to jump on it and write typescript definition files for it if need be.
On the data structures and immutability front, things are a bit better with Immutable.js but it would be great to wrap the structures in Monads so operations on them could be better chained.
Actually, string as the TypeScript type can also accept null:
function concat(a: string, b: string):string {
return a + b;
}
concat(null, null);
Does this answer your question?
