chickadee » scheme » base » call-with-port

It is an error if proc does not accept one argument. The call-with-port procedure calls proc with port as an argument. If proc returns, then the port is closed automatically and the values yielded by the proc are returned. If

proc does not return, then the port must 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 resume it. 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-port.

Ports represent input and output devices. To Scheme, an input port is a Scheme object that can deliver characters upon command, while an output port is a Scheme object that can accept characters.