Keyword Reference

This appendix lists all reserved keywords in Fe, organized by category.

Declaration Keywords

Keyword	Description
const	Declares a compile-time constant
let	Declares an immutable local binding
var	Declares a mutable local binding, or a mutable owned parameter (var x: own T)
fn	Declares a function
struct	Declares a struct type
enum	Declares an enum type
trait	Declares a trait
impl	Implements methods or traits for a type
type	Declares a type alias
contract	Declares a smart contract
msg	Declares a message type group
pub	Makes an item publicly visible
extern	Declares external items

Control Flow Keywords

Keyword	Description
if	Conditional branch
else	Alternative branch
match	Pattern matching expression
for	Loop over a range, array, or other collection
while	Loop while condition is true
break	Exit a loop early
continue	Skip to next loop iteration
return	Return from a function
yield	Grant the caller access in a projection, then run code after its last use

Type Keywords

Keyword	Description
Self	The implementing type in trait/impl
self	The receiver in methods
true	Boolean true literal
false	Boolean false literal

Effect Keywords

Keyword	Description
uses	Declares effect requirements
with	Binds values to effects

Contract Keywords

Keyword	Description
init	Contract constructor block
recv	Message receive block

Ownership & Access Keywords

Keyword	Description
own	Takes ownership of a value
mut	Grants mutable access to a place (x: mut T, mut self, let h = mut p.x)
ref	Grants read access to a place (let r = ref p.x, for ref x in xs)
mut?	Makes a function usable at either ref or mut
unsafe	Marks an unsafe fn, unsafe { .. } block, unsafe field, trait or impl

Module Keywords

Keyword	Description
use	Import items from other modules
mod	Declares a module
ingot	Refers to the current ingot root
super	Refers to the parent module

Other Keywords

Keyword	Description
as	Type casting
in	Used in for loops

Contextual Keywords

These identifiers have special meaning in certain contexts:

Keyword	Context	Description
where	Generic bounds	Introduces where clauses and const predicates
shape	Traits	Declares an associated shape or a shape parameter
_	Patterns	Wildcard pattern, ignores value

Quick Reference by Category

Declarations

const MAX_SUPPLY: u256 = 1000000
let balance = 0
var counter = 0
fn transfer() { }
struct Token { }
enum Status { }
trait Hashable { }
impl Hashable for Token { }
pub contract MyContract { }
msg TokenMsg { }

Control Flow

if condition { } else { }
match value { }
for item in items { }
while condition { }
return value

Effects

fn foo() uses (storage: Storage) { }
fn foo() uses (storage: mut Storage) { }
with (storage: Storage = store) { }

Contracts

contract Token {
    init() { }
    recv Msg {
    }
}

Reserved for Future Use

The following keywords are reserved and may not be used as identifiers:

• async
• await
• dyn
• move
• static
• crate

Summary

Fe has approximately 40 keywords covering:

• 13 declaration keywords
• 9 control flow keywords
• 4 type keywords
• 2 effect keywords
• 2 contract keywords
• 5 ownership/access keywords
• 4 module keywords
• 2 other keywords
• 3 contextual keywords