Web Development with ReasonML

Working with Types

To see an example of ReasonML’s attention to detail about types, let’s modify the preceding price calculation program to handle prices that aren’t integers, such as $14.50. If we change the code to read:

let qty = 7;
let price = 14.50;
let total = qty * price;
Js.log2("The total price is $", total);

We get this compile error:

  We've found a bug for you!
  /path/to/code/first-project/src/FloatPrice.re 3:19-23

  1 │ let qty = 7;
  2 │ let price = 14.50;
  3 │ let total = qty * price;
  4 │ Js.log2("The total price is $", total);

  This has type:
    float
  But somewhere wanted:
    int

You can convert a float to a int with int_of_float.
If this is a literal, you want a number without a trailing ...