peek-char -- r7rs Definition

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Kind

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procedure;

Implemented by

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• peek-char (from vonuvoli);

Procedure signature

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Procedure variants:

• (() -> (character-or-eof))
  • inputs: none;
  • output: a value of type character-or-eof;
• ((textual-input-port-eof) -> (eof-object))
  • input: a value of type textual-input-port-eof;
  • output: a value of type eof-object;
• ((textual-input-port-open) -> (character-or-eof))
  • input: a value of type textual-input-port-open;
  • output: a value of type character-or-eof;

Exports

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• scheme:base -- (scheme base);

Exports recursive

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• scheme -- (scheme);

Description

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(peek-char)
(peek-char port)

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 difference 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.

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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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• character-or-eof;
• textual-input-port-eof;
• eof-object;
• textual-input-port-open;