Line Oriented and Delimited Text

The delimited-I/O module can be accessed with:

(use-modules (ice-9 rdelim))

It can be used to read or write lines of text, or read text delimited by a specified set of characters.

Scheme Procedure: read-line [port] [handle-delim]

Return a line of text from port if specified, otherwise from the value returned by (current-input-port). Under Unix, a line of text is terminated by the first end-of-line character or by end-of-file.

If handle-delim is specified, it should be one of the following symbols:

trim

Discard the terminating delimiter. This is the default, but it will be impossible to tell whether the read terminated with a delimiter or end-of-file.

concat

Append the terminating delimiter (if any) to the returned string.

peek

Push the terminating delimiter (if any) back on to the port.

split

Return a pair containing the string read from the port and the terminating delimiter or end-of-file object.

Scheme Procedure: read-line! buf [port]

Read a line of text into the supplied string buf and return the number of characters added to buf. If buf is filled, then #f is returned. Read from port if specified, otherwise from the value returned by (current-input-port).

Scheme Procedure: read-delimited delims [port] [handle-delim]

Read text until one of the characters in the string delims is found or end-of-file is reached. Read from port if supplied, otherwise from the value returned by (current-input-port). handle-delim takes the same values as described for read-line.

Scheme Procedure: read-delimited! delims buf [port] [handle-delim] [start] [end]

Read text into the supplied string buf.

If a delimiter was found, return the number of characters written, except if handle-delim is split, in which case the return value is a pair, as noted above.

As a special case, if port was already at end-of-stream, the EOF object is returned. Also, if no characters were written because the buffer was full, #f is returned.

It’s something of a wacky interface, to be honest.

Scheme Procedure: %read-delimited! delims str gobble [port [start [end]]]

C Function: scm_read_delimited_x (delims, str, gobble, port, start, end)

Read characters from port into str until one of the characters in the delims string is encountered. If gobble is true, discard the delimiter character; otherwise, leave it in the input stream for the next read. If port is not specified, use the value of (current-input-port). If start or end are specified, store data only into the substring of str bounded by start and end (which default to the beginning and end of the string, respectively).

Return a pair consisting of the delimiter that terminated the string and the number of characters read. If reading stopped at the end of file, the delimiter returned is the eof-object; if the string was filled without encountering a delimiter, this value is #f.

Scheme Procedure: %read-line [port]

C Function: scm_read_line (port)

Read a newline-terminated line from port, allocating storage as necessary. The newline terminator (if any) is removed from the string, and a pair consisting of the line and its delimiter is returned. The delimiter may be either a newline or the eof-object; if %read-line is called at the end of file, it returns the pair (#<eof> . #<eof>).

Scheme Procedure: write-line obj [port]

C Function: scm_write_line (obj, port)

Display obj and a newline character to port. If port is not specified, (current-output-port) is used. This procedure is equivalent to:

(display obj [port])
(newline [port])

Scheme Procedure: for-rdelim-from-port port proc rdelim-proc [#:stop-pred=eof-object?]

For every unit provided by (rdelim-proc port), provide this unit(rdelim) to proc to be processed. This will continue throughout port until stop-pred returns #t. stop-pred is eof-object? by default. rdelim-proc has to advance through port with every call made to it.

Scheme Procedure: for-delimited-from-port port proc [#:delims=”\n”] [#:handle-delim=’trim]

Call proc for every line delimited by delims from port.

Scheme Procedure: for-line-in-file file proc [#:encoding=#f] [#:guess-encoding=#f]

Call proc for every line in file. file must be a filename string.

The line provided to proc is guaranteed to be a string.