The let Expression

The let expression allows for defining variables. A simple example of a variable declaration would be:

let name = "bob"

Here we define a variable named name and assign it the string bob. By default, all variables are immutable (ie, cannot be modified). The type of name is autodeduced as type string because "bob" is a string.

Variables in the Cicada DSL are block-scoped, meaning they are only available in the block they define. Variables can also be shadowed, meaning they can be redefined without any errors:

let num = 1
let num = num * 2

In this contrived example above we first assign the value 1 to num, then create a new variable (also called num) and assign it the value 2. Whenever num is referenced now, the most recently assigned num, in this case, the second one, will be used.


While let can be used as a statement (that is, on it's own line), it can also be used in other expressions such as the if expression:

if let number = 123:
  echo your number is (number)

# Error, number is not defined here.
echo (number)

In the above example, number is created using a let expression. Since 123 is truthy, the if condition passes, and the first echo command would be ran. The second echo command causes an error though, since number is only scoped to the body of the if expression.

Mutable Variables

You can use the mut keyword to make a variable mutable:

let mut num = 123

num = 456

echo Your number is (num)