We've covered a few basic functions, now we'll put them to the test! We'll make a little calculator. The program is simple but nicely demonstrates how all the functions we've talked about work together. Let's see!

The calculator will work something like this:

$ funkycmd calculator.fn
2 + 2
4
9 / 2
4.5
12 * 12
144

It will support four operators: +, -, *, /. It will only support one operator per expression.

The first thing will be to scan the expression. The expression consists of three words on a single line, so it'll be best to use scan three times:

func main : IO =
    scan \x-str
    scan \op
    scan \y-str
    # TODO

Good. Now, x-str and y-str are strings because that's what scan gives us. In order to perform computations, we need to convert them to floats first.

$ funkycmd -types
> float
Int -> Float
String -> Float

The second overload of the float function seems to be doing just that, so let's use it (there's an analogous function for integers called int):

func main : IO =
    scan \x-str
    scan \op
    scan \y-str
    let (float x-str) \x
    let (float y-str) \y
    # TODO

We saved the converted numbers in the x and y variables.

Now we need to compute the result and print it. For example, if the operator is +, the result will be string; x + y. Here we can exploit the if function's ability to form if/else chains:

if (op == "+") (string; x + y);
if (op == "-") (string; x - y);
if (op == "*") (string; x * y);
if (op == "/") (string; x / y);
"invalid operator: " ++ op

The last line becomes the result if the operator is not among the supported ones. Now that we've got the result, all that's left it to print it and continue the loop:

func main : IO =
    scan \x-str
    scan \op
    scan \y-str
    let (float x-str) \x
    let (float y-str) \y
    println (
        if (op == "+") (string; x + y);
        if (op == "-") (string; x - y);
        if (op == "*") (string; x * y);
        if (op == "/") (string; x / y);
        "invalid operator: " ++ op
    );
    main

And that's it! Now go and experiment yourself! When you come back, we'll start learning about making our own functions and types.