macroexpand-1

Symbol: macroexpand-1

Syntax: (macroexpand-1 form ns)

Use-case: Apply a single macro-expansion step to a source form. Useful for debugging macros: see exactly one transformation before the compiler takes over. For full expansion to a non-macro form, use macroexpand.

Behaviour: Takes the module compiler for ns through get-compiler, finds a compiled binding for the form’s head, and if it is a Syntax transformer, runs one handle_expand pass. If the head is not a macro, or no transformer matches, the form is returned unchanged.

When the expansion is a single-expression begin wrapper, that wrapper is stripped so the result is the inner expression.

The form must already be a read source object (a pair or atom). To expand from written surface syntax, use the macroexpandq-1 macro or quote the form yourself.

Relation to the macro: (macroexpand-1 form) and (macroexpand-1 form ns) are handled by the compile/macroexpand-1 macro, which expands to (call macroexpand-1 ...) with (globals) when the namespace argument is omitted. See compile/macroexpand-1.

Examples:

>>> (macroexpand-1 '(when condition action))
(cond [condition action] [else: None])

;; Explicit namespace
(macroexpand-1 some-form my-ns)

The macroexpandq-1 macro quotes for you, so the form is written unquoted:

>>> (macroexpandq-1 (when condition action))
(cond [condition action] [else: None])