char-ready? -- r7rs Definition

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Kind

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predicate;

Implemented by

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• char-ready? (from vonuvoli);

Procedure signature

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Procedure variants:

• (() -> (boolean))
  • inputs: none;
  • output: a value of type boolean;
• ((textual-input-port-eof) -> (true))
  • input: a value of type textual-input-port-eof;
  • output: a value of type true;
• ((textual-input-port-open) -> (boolean))
  • input: a value of type textual-input-port-open;
  • output: a value of type boolean;

Exports

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• scheme:base -- (scheme base);

Exports recursive

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• scheme -- (scheme);

Description

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(char-ready?)
(char-ready? port)

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 possible for a program to accept characters from interactive ports without getting stuck waiting for input. Any input editors associated 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.

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The text herein was sourced and adapted as described in the "R7RS attribution of various text snippets" appendix.

Referenced-types

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• boolean;
• textual-input-port-eof;
• true;
• textual-input-port-open;