Input

If port is omitted from any input procedure, it defaults to the value returned by (current-input-port). It is an error to attempt an input operation on a closed port.

(read ) read library procedure
(read port ) read library procedure
The read procedure converts external representations of Scheme objects into the objects themselves. That is, it is a parser for the non-terminal {datum} (see section 6.4). It returns the next object parsable from the given textual input port, updating port to point to the first character past the end of the external representation of the object.

Implementations may support extended syntax to represent record types or other types that do not have datum representations.

If an end of file is encountered in the input before any characters are found that can begin an object, then an end-of-file object is returned. The port remains open, and further attempts to read will also return an end-of-file object. If an end of file is encountered after the beginning of an object's external representation, but the external representation is incomplete and therefore not parsable, an error that satisfies read-error? is signaled.

(read-char ) procedure
(read-char port ) procedure
Returns the next character available from the textual input port, updating the port to point to the following character. If no more characters are available, an end-of-file object is returned.

(peek-char ) procedure
(peek-char port ) procedure
Returns the next character available from the textual input port, but without updating the port to point to the following character. If no more characters are available, an end-of-file object is returned.

Note: The value returned by a call to peek-char is the same as the value that would have been returned by a call to read-char with the same port. The only diㄦence is that the very next call to read-char or peek-char on that port will return the value returned by the preceding call to peek-char. In particular, a call to peek-char on an interactive port will hang waiting for input whenever a call to read-char would have hung. (read-line) procedure

(read-line port ) procedure
Returns the next line of text available from the textual input port, updating the port to point to the following character. If an end of line is read, a string containing all of the text up to (but not including) the end of line is returned, and the port is updated to point just past the end of line. If an end of file is encountered before any end of line is read, but some characters have been read, a string containing those characters is returned. If an end of file is encountered before any characters are read, an end-of-file object is returned. For the purpose of this procedure, an end of line consists of either a linefeed character, a carriage 58 Revised7 Scheme followed by a linefeed character. Implementations may also recognize other end of line characters or sequences.

(eof-object? obj ) procedure
Returns #t if obj is an end-of-file object, otherwise returns #f. No end-of-file object will ever be an object that can be read in using read.

(eof-object ) procedure
Returns an end-of-file object, not necessarily unique.

(char-ready? ) procedure
(char-ready? port ) procedure
Returns #t if a character is ready on the textual input port and returns #f otherwise. If char-ready returns #t then the next read-char operation on the given port is guaranteed not to hang. If the port is at end of file then char-ready? returns #t.

Rationale: The char-ready? procedure exists to make it pos- sible for a program to accept characters from interactive ports without getting stuck waiting for input. Any input editors as- sociated with such ports must ensure that characters whose existence has been asserted by char-ready? cannot be removed from the input. If char-ready? were to return #f at end of file, a port at end of file would be indistinguishable from an interactive port that has no ready characters.

(read-string k ) procedure
(read-string k port ) procedure
Reads the next k characters, or as many as are available before the end of file, from the textual input port into a newly allocated string in left-to-right order and returns the string. If no characters are available before the end of file, an end-of-file object is returned.

(read-bytevector k port ) procedure
Reads the next k bytes, or as many as are available before the end of file, from the binary input port into a newly allocated bytevector in left-to-right order and returns the bytevector. If no bytes are available before the end of file, an end-of-file object is returned.

husk-scheme online documentation rev 3.19.3 (2016.07.10)