Search⌘ K
Home
Courses
Functional Programming with ReasonML

Strings

Explore how to define and manipulate strings in ReasonML. Learn about string creation, accessing characters by index, concatenating strings, determining length, and checking for character existence. This lesson builds foundational skills for handling text data in ReasonML applications.

We'll cover the following...

Definition

A string is a collection of characters joined together.

Double quotes are used to enclose the value of a string, e.g., "Hello".

Since a string is a collection, we can access each individual character in the string as well. The characters are indexed from 0 to n-1 where n is the length of the string.

Unlike characters, strings can be of any length, including 1.

We’ve already seen an example of a string in the first lesson when we printed “Hello World”.

We can print strings using Js.log() (prints in a new line each time) or print_string() (prints in the same line):

Reason
Js.log("Hello World");
/* Alternate method */
print_string("Hello World");

Concatenation

Reason allows us to append strings together using the ++ operator.

Reason
print_string("Hello W" ++ "orld" ++ "!");

String Length

The length of a string can be obtained using the String.length() method. Keep in mind that an empty space in a string also counts as an element.

Reason
Js.log(String.length("Hello World")); /* 11 */
Js.log(String.length("a")); /* 1 */

Accessing Elements

A character in a string can be accessed using its index. The simplest approach is to use the .[] notation:

("Hello World").[4]

The line above will return o as it is the fifth character in the string. The index is enclosed inside the square brackets. This process is known as indexing.

Here it is in action:

Reason
print_char(("Hello World").[4]);

An alternative approach is to use the String.get() method, but we’ll leave that as a self-exercise.

The Existence of a Character

We can check if a particular character exists in a given string using the String.contains() method. It requires the following template:

String.contains(string, char)

Here’s the method in action:

Reason
Js.log(String.contains("Hello World", 'e'));

This is helpful when we need to do a character search in a large piece of string.

The last data type we need to discuss is the unit, but we’ll leave that for a later section in order to give it context. For now, let’s move on to the concept of polymorphic operators.