Declare Functions in Reason

Nik Graf
InstructorNik Graf

Share this video with your friends

Send Tweet

In this lesson we walk through how to declare functions in ReasonML. Declaring and using functions is straightforward. Still there are a handful great features not available in a lot of other languages like labeled arguments or auto currying. Both are explained in this lesson.

jmmendivil
jmmendivil
~ 2 years ago

What do you mean with avoid a lot of tedious switch expressions (06:53)? The example uses a function with a switch in it, can you please provide another example?

Nik Graf
Nik Grafinstructor
~ 2 years ago

The example uses ~middleName=?someName. Without that you would need to switch on someName. Does that help?

JP Lew
JP Lew
~ a year ago

I believe the behaviour described in the video has become outdated.

In the latest version of rtop (2.2.0), I get the following output:

Reason # let name = (~firstName, ~middleName="Francis", ~lastName) => {
  firstName ++ " " ++ middleName ++ " " ++ lastName;
};
let name:
  (~firstName: string, ~middleName: string=?, ~lastName: string) => string =
  <fun>;
Reason # name(~firstName="Jane", ~middleName="Kim", ~lastName="Doe");
- : string = "Jane Kim Doe"
Reason # name(~firstName="Jane", ~lastName="Doe");
- : (~middleName: string=?) => string = <fun>
Reason # name(~firstName="Jane", ~lastName="Doe")();
Error: The function applied to this argument has type
         (~middleName: string=?) => string
This argument cannot be applied without label
Reason # name(~firstName="Jane", ~lastName="Doe", ());
Error: The function applied to this argument has type
         (~middleName: string=?) => string
This argument cannot be applied without label
JP Lew
JP Lew
~ a year ago

sorry, please ignore the above comment, I didn't notice the positional parameter () at the end! ```name(~firstName="Jane", ~middleName="Kim", ~lastName="Doe", ());`