Foreign Strings

A foreign-string is a kind of byte-vector whose entity is held somewhere outside EusLisp's heap. While a normal string is represented by a sequence of bytes and its length, a foreign-string holds the length and the address of the string entity. Although foreign-string is a string, some string and sequence functions cannot be applicable. Only length, aref, replace, subseq and copy-seq recognize the foreign-string, and application of other functions may cause a crash.

A foreign-string may refer to a part of I/O space usually taken in /dev/a??d?? special file where ?? is either 32 or 16. In case the device attached in one of these I/O space only responds to byte access, replace always copies element byte by byte, which is relatively slow when a large chunk of memory is accessed consecutively.

make-foreign-string address length [function]

makes an instance of foreign-string located at address and spanning for length bytes. For example, (make-foreign-string (unix:malloc 32) 32) makes a reference to a 32-byte memory located outside EusLisp's heap.