6.12.8 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.