Syntax Reference

Syntax reference

This is a navigation reference, not a substitute for the worked explanations. Placeholders below describe forms rather than executable programs.

Declarations

Form	Guide
let $name[: Type] [= expression]	Variables
let ($a, $b) = expression	Exact-length destructuring in Variables
let _ = expression	Evaluate and discard
let export $name = expression	Environment
let type $name = Type	Convert an existing environment binding
fn name($arg: Type): Result { ... }	Functions
fn ($arg: Type): Result { ... }	Closures
fn Type::method(...): Result { ... }	Methods
type Name = Type	Distinct named types
struct Name { field: Type }	Structs
enum Name { First, Second }	Enums
error struct Name { ... }	Errors
alias name = command default_argument	Commands
pub declaration	Module visibility
import path::{ Name } [when expression]	Modules
[when expression] declaration	Conditional code

An omitted function result is (), including methods and anonymous functions. Write : any explicitly for a dynamic result. See function contracts.

Type forms

Type	Meaning
Integer, Float, Boolean, String	Scalar types
Number	Integer or Float constraint
any	General value type
()	Unit / no value
T | U, T | ()	Union; optional union
[T]	Array of T
[K: V]	Hash with key K, value V
[T, U]	Fixed-shaped item/row type
fn(T, U): R	First-class function prototype
$self.value_type, $self.key_type	Dependent collection method annotations

[Integer] in value position creates a typed empty array. [(Integer)] contains one type object. Hash typed-empty syntax is [String: Integer].

Expressions and operators

Forms	Guide
+ - * / %	Arithmetic
== != < <= > >=	Equality and numeric ordering
! && ||	Boolean conversion and short-circuit logic
a..b, a..=b	Ranges
$array[index], $array[start..end]	Arrays
$map[key]	Hash maps
$value.member, $value.::field	Methods and raw fields
Type(value)	Explicit conversion
if condition { a } else { b }	Control flow
match value { pattern => { result } }	Matching
source | stage	Pipelines
source format:|:Type stage	Pipeline conversion
Aligned \- and vertical | guides	Pipeline splits
command -> target	Redirection
::command	External command lookup

Arithmetic multiplication/division/remainder bind before addition/subtraction; comparisons bind before &&, and && before ||. Pipeline stages associate left to right. Use parentheses to state grouping explicitly, especially around invocations inside an expression. Parentheses enclosing a function prototype control whether a union belongs to its return type or to the function value.

Statements can be separated by newlines or ;. A backslash continues a line. # begins a comment. Double-quoted Strings interpolate; single-quoted Strings remain literal. $array... spreads arguments/items; bare $ means pipeline input.

#tab-size N in the file header selects tab stops for that source. Precedence is file directive, explicit --tab-width N, $SHELLY_TAB_SIZE, then 4. See split alignment and tabs.

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