Chicken » Unit ports

Unit ports

This unit contains various extended port definitions. This unit is used by default, unless the program is compiled with the -explicit-use option.

Input/output port extensions

with-output-to-port

(with-output-to-port PORT THUNK) procedure: Call procedure THUNK with the current output-port temporarily bound to PORT.

make-input-port

(make-input-port READ-CHAR CHAR-READY? CLOSE [PEEK-CHAR [READ-STRING! [READ-LINE]]]) procedure

Returns a custom input port. Common operations on this port are handled by the given parameters, which should be procedures of no arguments. The following arguments are all different kinds of reader procedures:

READ-CHAR is the most fundamental reader, and must always be present. It is a thunk which is called when the next character is to be read and it should return a character or #!eof.
CHAR-READY? is a thunk which is called when char-ready? is called on this port and should return #t or #f.
CLOSE is a thunk which is called when the port is closed.
PEEK-CHAR is a thunk which is called when peek-char is called on this port and should return a character or #!eof. If it is not provided or #f, READ-CHAR will be used instead and the created port object handles peeking automatically (by calling READ and buffering the character).
READ-STRING! is called when read-string! is called (or the higher-level non-mutating read-string). It will be invoked with 4 arguments: the port created by make-input-port, the number of bytes to read, a string (or sometimes a blob) to read into (which may be assumed to be big enough to hold the data) and the offset into the buffer at which to put the data to read. It should return the number of bytes that have successfully been read, which should always be equal to the requested bytes unless EOF was hit, in which case it can be less. If this procedure is not provided or #f, the buffer will be filled by repeated reads to READ-CHAR.
READ-LINE is called when read-line is called. It will be invoked with two arguments: the port created by make-input-port and the maximum number of characters to read (or #f). If this procedure is not provided or #f, the buffer will be filled by repeated reads to READ-CHAR.

All the optional procedures except for PEEK-CHAR are responsible for updating the port's position, which currently can only be done via low-level slot accessors like ##sys#setslot; slot 4 is the row number (ie, the line) and slot 5 is the column number (ie, the character on the line). If the port's positions are not updated, port-position won't work.

make-output-port

(make-output-port WRITE CLOSE [FLUSH]) procedure: Returns a custom output port. Common operations on this port are handled by the given parameters, which should be procedures. WRITE is called when output is sent to the port and receives a single argument, a string. CLOSE is called when the port is closed and should be a procedure of no arguments. FLUSH (if provided) is called for flushing the output port.

with-error-output-to-port

(with-error-output-to-port PORT THUNK) procedure: Call procedure THUNK with the current error output-port temporarily bound to PORT.

with-input-from-port

(with-input-from-port PORT THUNK) procedure: Call procedure THUNK with the current input-port temporarily bound to PORT.

String-port extensions

call-with-input-string

(call-with-input-string STRING PROC) procedure: Calls the procedure PROC with a single argument that is a string-input-port with the contents of STRING.

call-with-output-string

(call-with-output-string PROC) procedure: Calls the procedure PROC with a single argument that is a string-output-port. Returns the accumulated output-string.

with-input-from-string

(with-input-from-string STRING THUNK) procedure: Call procedure THUNK with the current input-port temporarily bound to an input-string-port with the contents of STRING.

with-output-to-string

(with-output-to-string THUNK) procedure: Call procedure THUNK with the current output-port temporarily bound to a string-output-port and return the accumulated output string.

Port iterators

port-for-each

(port-for-each FN THUNK) procedure: Apply FN to successive results of calling the zero argument procedure THUNK (typically read) until it returns #!eof, discarding the results.

port-map

(port-map FN THUNK) procedure: Apply FN to successive results of calling the zero argument procedure THUNK (typically read) until it returns #!eof, returning a list of the collected results.

port-fold

(port-fold FN ACC THUNK) procedure: Apply FN to successive results of calling the zero argument procedure THUNK, (typically read) passing the ACC value as the second argument. The FN result becomes the new ACC value. When THUNK returns #!eof, the last FN result is returned.

copy-port

(copy-port FROM TO [READ [WRITE]]) procedure

Reads all remaining data from port FROM using the reader procedure READ and writes it to port TO using the writer procedure WRITE. READ defaults to read-char and WRITE to write-char. Note that this procedure does not check FROM and TO for being ports, so the reader and writer procedures may perform arbitrary operations as long as they can be invoked as (READ FROM) and (WRITE X TO), respectively. copy-port returns an undefined value.

copy-port was introduced in CHICKEN 4.6.0.

Funky ports

make-broadcast-port

(make-broadcast-port PORT ...) procedure: Returns a custom output port that emits everything written into it to the ports given as PORT .... Closing the broadcast port does not close any of the argument ports.

make-concatenated-port

(make-concatenated-port PORT1 PORT2 ...) procedure: Returns a custom input port that reads its input from PORT1, until it is empty, then from PORT2 and so on. Closing the concatenated port does not close any of the argument ports.

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