chickadee » scheme » call-with-output-file

call-with-input-file string procprocedure
call-with-output-file string procprocedure

String should be a string naming a file, and proc should be a procedure that accepts one argument. For call-with-input-file, the file should already exist; for call-with-output-file, the effect is unspecified if the file already exists. These procedures call proc with one argument: the port obtained by opening the named file for input or output. If the file cannot be opened, an error is signalled. If proc returns, then the port is closed automatically and the value(s) yielded by the proc is (are) returned. If proc does not return, then the port will not be closed automatically unless it is possible to prove that the port will never again be used for a read or write operation.

Rationale: Because Scheme's escape procedures have unlimited extent, it is possible to escape from the current continuation but later to escape back in. If implementations were permitted to close the port on any escape from the current continuation, then it would be impossible to write portable code using both call-with-current-continuation and call-with-input-file or call-with-output-file.