peek-char
builtin-function
(peek-char &optional (peek-type null) (stream $stdin) (eof-error? true) (eof-value null))
Peeks at a character from a TextReader stream.
When peek-type equals null or false peek-char is equivalent to
read-char followed by unread-char. When peek-type is true, peek-char
ends up peeking at the first non-whitespace character (by really reading the
whitespace characters). When peek-type is a character, peek-char ends up
peeking at that character (by really reading the characters that are not equal).