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#### 10.2.4 Character input stream methods

These generic functions are used to implement subclasses of fundamental-input-stream:

— Generic Function: sb-gray:stream-peek-char stream

> This is used to implement `peek-char`; this corresponds to `peek-type` of `nil`. It returns either a character or `:eof`. The default method calls `stream-read-char` and `stream-unread-char`.

— Generic Function: sb-gray:stream-read-char-no-hang stream

> This is used to implement `read-char-no-hang`. It returns either a character, or `nil` if no input is currently available, or `:eof` if end-of-file is reached. The default method provided by `fundamental-character-input-stream` simply calls `stream-read-char`; this is sufficient for file streams, but interactive streams should define their own method.

— Generic Function: sb-gray:stream-read-char stream

> Read one character from the stream. Return either a character object, or the symbol `:eof` if the stream is at end-of-file. Every subclass of `fundamental-character-input-stream` must define a method for this function.

— Generic Function: sb-gray:stream-read-line stream

> This is used by `read-line`. A string is returned as the first value. The second value is true if the string was terminated by end-of-file instead of the end of a line. The default method uses repeated calls to `stream-read-char`.

— Generic Function: sb-gray:stream-listen stream

> This is used by `listen`. It returns true or false. The default method uses `stream-read-char-no-hang` and `stream-unread-char`. Most streams should define their own method since it will usually be trivial and will always be more efficient than the default method.

— Generic Function: sb-gray:stream-unread-char stream character

> Un-do the last call to `stream-read-char`, as in `unread-char`. Return `nil`. Every subclass of `fundamental-character-input-stream` must define a method for this function.