7.14 Syntax Objects in Macros🔗ℹ

Throws a syntax-error message concerning in_stx. If message is not provided, the message is "bad syntax". If at_stx is provided, it should be something like an enclosed form of in_stx to provide extra context. Alternatively, at_stx can be a list of syntax objects, in which case all syntax objects provide extra contexts, least-specific to most-specific.

Returns the compile-time value of name, if available, in the space specified by in_space. If no compile-time value is available, then fail is called if it is a procedure of 0 arguments, otherwise fail is returned.

The default fail is a procedure that throws an exception.

Checks whether stx1 at phase phase1 refers to the same binding as stx2 at phase2 within the space reflected by in_space.

Checks whether stx1 and stx2 have the same name (as returned by Syntax.unwrap on an identifier, for example) and the same scopes at phase.

When stx1 or stx2 is a dotted name, then both must be dotted names where each dotted component has the same name and scopes.

Returns a syntax object like stx, but where scopes indicating that the syntax object is macro-introduced are flipped. The result is stx unmodified when not during the expansion of a macro.

Macro-introduction is detected by flipping scopes to the input of a macro, then flipping scopes on the macro’s result, so that the two flip operations cancel for any part of the macro’s input that is used in the macro’s output.

A macro can flip introduction to implement a non-hygienic expansion for an introduced identifier. Flipping introduction may also be helpful when syntax is preserved through side channels, or in unusual cases when checking for the originaless of a term with Syntax.is_original.

Matches an integer or #false.

A phase-level integer corresponds to a phase of evaluation, especially relative to the main body of a module. Phase level 0 corresponds to a module’s run time, 1 corresponds to expansion time for run-time forms, and so on. A phase level of #false corresponds to the label phase, like meta_label.

Returns the phase of expression forms currently being expanded, or 0 if no expansion is in progress.

Unquote binding operator for use with $. It matches a syntax object for an identifier or operator, where the identifier or operator’s binding is the same as op_or_id_name in the SpaceMeta reflected by space_expr (e.g., expr_meta.space).