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0 pointsfalcolas11y ago0 comments

> Just get the machine to do it.

Exactly. Many people already use IDEs, or programs which provide auto-completion or hinting of the types a function accepts when writing out a function name - the type does not need to be explicitly written for the machine to identify the type of the function.

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xxgreg11y ago· 2 in thread

What types does the following function expect for the arguments a and b, and what type does it return?

What should an IDE tell the user about the types of a and b in the completion popup?

function foo(a, b) { return a + b; }

the_af11y ago

In some static languages, the inferred type for a and b could be Numeric, and foo's type could be:

    (Numeric, Numeric) -> Numeric

Which seems good enough to me.

But what if + is also String concatenation? Or any other overloading of "+". Then maybe the type of a and b is Something_that_can_be_+ed. The user can then think "ok, I'll pass a couple of Ints to obtain an Int, or a couple of Strings to obtain a String!". This also seems useful to me.

xxgreg11y ago

Now consider the following buggy code:

    var price = document.querySelector('input#price').value; // "10"
    var tax = document.querySelector('input#tax').value; // "1"
    var total = foo(price, tax); // "101"

This will concatenate two strings together, even though the author intended to add two numbers. If the foo function had been annotated as numeric the IDE could have provided a warning about the incorrect types and put a squigly line under foo.

I find this type of fast feedback improves programmer productivity. It means that you get warned straight away, and don't have to do a trip through the debugger to find the problem.

Just because the compiler can infer that a specific type could be passed to a function, that does not mean that the developer intended that function to be used with that type.

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