- (er-macro-rules (%sym ...) (code0 xpr0) (code1 xpr1) ...)syntax
references a renamed version of sym ... under the name %sym ... and pairs the differnt macro-codes code0 code1 ... with expressions xpr0 xpr1 ..., which usually evalute to backquoted templates.
This macro is unhygienic by design, it introduces the symbol compare? into its scope.