Statements and expressions

In Firefly, the body of functions and methods consist of zero or more statements, separated by ; .

When ; is the last token on a line, it can be omitted.

A statement is either a local function definition , a local variable definition, an assignment or an expression.

Field assignments were covered in user defined types .

Local variables

Local variables need an initial value: 

let x = 42

This defines immutable local variable x: Int with the value 42 .

Variables can be reffered to by name: 

x + x       // Returns 84

The type of a variable can be stated explicitly: 

let y: String = "Hello"

Mutable variables are introduced using the mutable keyword: 

mutable z = 1

This works like let , except that you're allowed to update mutable variables by assigning to them: 

z = 2       // z is now 2
z += 2      // z is now 4
z -= 1      // z is now 3

Expressions

Expressions can be one of the following syntactic constructs: 

42          // Int literal
42.0        // Float literal
'a'         // Char literal
"foo"       // String literal
[]          // List literal
{}          // Function literal
()          // Record literal
True        // Variant construction
x           // Variable
_           // Anonymous parameter
f()         // Function call
x.y         // Field access
x.V()       // Copy construction
x.{_}       // Piping
!x          // Unary operator
a + b       // Binary operator
(a + b) * c // Grouping parenthesis

Binary operators are left associative and the operator precedence is as follows, lowest to highest:

  • ||
  • &&
  • != ==
  • <= >= < >
  • + -
  • * / %
  • ^
  • f()
  • x.y x.V() x.{_}

Unary operators ! and - have higher precedence than ^ and lower precedence than f() .

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