3.5 Assignment Macros🔗ℹ

The left-hand input to the macro is not a parsed expression, but instead a parsed value that encapsulates both a mutator and accessor for the target mutable component. The expansion of the macro can use another assignment operator, or it can use assign_meta.unpack_left to extract functions for the target and assemble them into an expression that is packed with assign_meta.pack_assignment.

Takes a syntax object that represents the parse left-hand side of an assignment operator, returning three pieces of information about the mutable target:

• an expression for a function of zero arguments that acts an accessor;

• an expression for a function of one argument that acts a mutator; and

• an identifier that reflects the target’s name, which is useful for inferring a name for certain kinds of values (such as functions) for the right-hand side.

An assignment macro defined with assign.macro can uses these pieces to construct an expression, and then wrap the expression via assign_meta.pack_assignment to serve as its result.

Converts a syntax object, which can be a multi-term syntax object, into an parsed term that represents an expression to implement an assignment operator’s expansion.

See assign.macro for an example.

A syntax class that matches by parsing an assignment, where the input starts with an assignment operator and continues as the operator expects (typically with a right-hand expression). The syntax-class arguments ref, set, and name must be an expression to produce an accessor function of zero arguments, an expression to produce a mutator function of one argument, and an identifier to use as the inferred name (if needed) for the right-hand value.

The value of a binding using assign_meta.AssignParsed is an opaque syntax object that represents the parsed assignment as an expression, while the group field holds a syntax object for the original terms that were parsed. The result also has a tail field that contains the remaining unparsed input.