Macros

The macros the bootstrap defines. Each expands at compile time to special forms or to other macros, and the expansion is then compiled as if it had been written. macroexpand at the REPL shows the expansion of any of them.

Binding and assignment

Macro	Does
set!	Store into a name, attribute, subscript, or ref, choosing the special by target shape
incr!, decr!	Add to or subtract from a binding in place
del!	Delete a name, attribute, or subscript
take!	Read a name, attribute, or subscript and clear it
bind!	Bind a name to a ref, typed by the target shape
ref	A ref to a name, attribute, subscript, or parameter
unassigned?, default!	Whether a location holds a value; store one unless it already does
let*	Sequential let, each binding seeing the ones before
let-values	let with unpacking
labels, flet	Local functions for a body, mutually recursive and not
define-parameter	Declare a dynamic parameter
define-environ	Bind a name to an environment variable
declare-exports	Name the module’s public features
entry-point	Mark the function a program runs once its module has loaded

Conditionals

Macro	Does
if	Two-armed conditional over cond
when, unless	One-armed conditionals
?	Conditional with a boolean default
bool	Truthiness as a boolean
None?	Identity test against the None singleton
has?	Membership
assert	Raise AssertionError unless a test holds; removable by pragma
pass	A no-op expression, and a bare control word

Definitions

Macro	Does
def	Define a function and bind it in the current scope
global	Prefix over var, def, class and syntax that binds the form at the module
class	Define a class and bind it in the current scope
super	The superclass proxy inside a method
decorate, decorate-subject	What @ lines lower to, and the per-decorator dispatch
when-main	Python’s __name__ guard; prefer entry-point for a program’s work

Iteration and collections

Macro	Does
each	A generator over a [var seq] binding, with when: and unless: filters
list-each	A list from the same shape
dict-each	A dict from key: and value: clauses
slice, item-slice	A slice object; a slice of a sequence
item*, attr*	Nested item and attribute chains
cadr … caddddr, first … fifth	Positions in a pair chain
function-compose	Compose functions right to left

Macros about macros

Macro	Does
syntax	A transformer bound at the module from top level, or for the rest of a body inside one
define-syntax	The Scheme-layer spelling: a transformer bound at the module, with any of the rule and match kinds or a bare form; its template names are kept apart from the use site, see Hygiene
extend-syntax	Add arms to an existing transformer
let-syntax	A transformer scoped to a body
inline-macro	Run a body at expand time and splice its result
datum	Capture a form with its source position for hygiene
datumq	The same without evaluating the argument; in a template, writes a form raw (-'form)
define-fence	Define a fence handler for a triple-backtick literal
macroexpand, macroexpand-1	Expand a form fully, or by one step
macroexpandq, macroexpandq-1	The same without quoting the form
compileq, evaluate, get-compiler	Compile, evaluate, and reach the compiler from a program
pragma	Set or read a module’s reader and compiler settings
help	Documentation for a name