Keyword Aliases

Some keywords have a more familiar spelling. The two spellings mean exactly the same thing.

Alias	Canonical	Purpose
fn	do	Function declaration
elif	or	Else-if branch
else	otherwise	Default branch
while	as_long_as	Condition loop
switch	when	Pattern match
case	is	Pattern match branch
defer	ensure	Deferred call
!in	not_in	Non-membership test

One spelling per file

Pick a spelling for each keyword and stick with it throughout a file. Using both spellings of the same keyword in one file is an error (E2088). Different files may choose differently, and each keyword is tracked on its own, so a file can write while and fn without also using elif.

This file uses the alias spellings throughout.

fn cleanup() {
    println("done")
}

fn describe(n i64) -> string {
    switch n {
        case 1 { return "one" }
        case 2 { return "two" }
        default { return "many" }
    }
    return ""
}

fn main() {
    defer cleanup()
    mut count i64 = 0
    while count < 3 {
        count++
    }
    if count == 0 {
        println("zero")
    } elif count == 3 {
        println("three")
    } else {
        println("other")
    }
    println(describe(2))
    mut names [string] = {"ann", "bo"}
    if "cy" !in names {
        println("cy is missing")
    }
}

Pairs that move together

Two of the keyword sets are joint: both words must come from the same side.

Style	Pattern match	Branch chain
Canonical	when with is	or with otherwise
Alias	switch with case	elif with else

So if a { } elif b { } otherwise { } is an error, and so is switch x { is 1 { } }. if and default are spelled the same in both styles.