How To Define Function In Elm
Let’s create our first Elm function that lives in a module. This post is part of the functional language series.
Our task is to create function that will calculate Croatian VAT value based on a product price. In the above image, you can see what you need to type in your favorite editor:
crois the function name. The same rules are applied as for the Elm module.
priceIt is the first parameter. If you need more, separate parameters with
=separates function signature from the body
- right from
=is a set of expressions (body). The meat part of the function. We multiply price with
0.25float because the Croatian VAT tax is
Let’s put our first Elm function through our processor:
Let’s make some errors
If you do not start function definition at first column:
The note has a meaningful error message. It says, “when something,” because it is tough to write a program that would identify programming constructs. But we know that we tried to define a function, so “when something” is in our case
Let’s make some runtime errors (do not forget to edit cro function and recompile it):
When you run function without a parameter, you get function signature printout:
<function> : Float -> Float
That means that
Vat.cro is a function where the input parameter is of type
Float and the return value is also
Float. If you would have more input parameters, let’s say two, the signature would be:
<function> : Float -> Float -> Float
A wrong parameter type triggered an error. The explanation is pretty good. We even got a hint on how to resolve our error. This is possible because, after the compilation, the program has more specific information about your function. In compile-time, it only has free text.
Remember. Do not be mad at the programming language author. Writing compilers is really hard.
Remember What You Learned
- how to define a function with parameters
- function return value
- no parentheses
- no return keyword, expression-oriented language
- how to call a function
- whitespaces as separation
- function signature using
- error messages