::=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.
The implementation has a set of feature identifiers which are “present”, as well as a set of libraries which can be imported. The value of a
feature-requirementis determined by replacing each
#tif it is present (and
library-nameis importable (and
#fotherwise); and then evaluating the resulting expression as a Scheme boolean expression under the normal interpretation of
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-9to check if the underlying Java is a specific version or newer. For example the name
java-7matches for either Java 7, Java 8, or newer, as reported by
You can use
class-exists:to check if
exists at compile-time. The identifier
class-exists:org.example.MyClassis roughly equivalent to the test
(library (org example MyClass)). (The latter has some special handling for
(srfi ...)as well as builtin Kawa classes.)
Returns a list of feature identifiers which
cond-expandtreats as true. This not a complete list - for example
class-exists:feature identifiers are not included. It is an error to modify this list. Here is an example of what
featuresmight return:(features) ⇒ (complex exact-complex full-unicode java-7 java-6 kawa ratios srfi-0 srfi-4 srfi-6 srfi-8 srfi-9 srfi-11 srfi-16 srfi-17 srfi-23 srfi-25 srfi-26 srfi-28 srfi-30 srfi-39 string-normalize-unicode threads)
These take one or more path names expressed as string literals, find corresponding files, read the contents of the files in the specified order as if by repeated applications of
read, and effectively replace the
beginform containing what was read from the files.
You can control the search path used for
includeby setting the
kawa.include.pathproperty. For example:$ kawa -Dkawa.include.path="|:/opt/kawa-includes"
"|"path element means to search relative to the directory containing the including source file. The default search path is
"|:."which means to first search the directory containing the including source file, and then search the directory specified by
The search path for
"|"before the search path used by
include, so it always searches first the directory containing the including source file. Note that if the default search path is used then
include-relativeare equivalent; there is only a difference if the
kawa.include.pathproperty changes the default.
include, except that it reads each file as if it began with the