Functional Programming with ReasonML/

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Strings

Strings

After the character type, we'll study its extension called string.

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.