::=a symbol which is the name or alias of a SRFI
cond-expandform tests for the existence of features at macro-expansion time. It either expands into the body of one of its clauses or signals an error during syntactic processing.
cond-expandexpands into the body of the first clause whose feature requirement is currently satisfied; the
elseclause, if present, is selected if none of the previous clauses is selected.
A feature requirement has an obvious interpretation as a logical formula, where the
feature-identifiervariables have meaning true if the feature corresponding to the feature identifier, as specified in the SRFI registry, is in effect at the location of the
cond-expandform, and false otherwise. A feature requirement is satisfied if its formula is true under this interpretation.
Examples:(cond-expand ((and srfi-1 srfi-10) (write 1)) ((or srfi-1 srfi-10) (write 2)) (else))(cond-expand (command-line (define (program-name) (car (argv)))))
The second example assumes that
command-lineis an alias for some feature which gives access to command line arguments. Note that an error will be signaled at macro-expansion time if this feature is not present.
You can use
java-6to check for Java 6 or Java 7, respectively, at compile-time.
You can use
class-exists:to check if
exists at compile-time.
Read the contents of the file at
pathas a sequence of forms, and treat the result as if the resulting forms were the forms of a
include, except that the
pathis relative to the path of the source-file containing the