; This is a syntactically correct but silly file.

partial     hel
complete    {partial}lo            ; Backward macro ref. only
digit       [0-9]
letter      [a-zA-Z]

%%

-?{digit}+    (cons 'integer yytext)   ; yytext contains
                                       ; the lexeme
-?{digit}+\.{digit}+[eE][-+]?{digit}+
              (cons                ; An action
               'float              ; spanning multiple
               yytext)             ; lines

;             (list 'semicolon)    ; Probably a mistake

begin         )list 'begin(        ; No error detected here
end                                ; The action is optional

\73           (list 'bell-3)       ; It does not match the
                                   ; char. # 7 followed by ‘3’
\0073         (list 'bell-3)       ; Neither does it
(\7)3         (list 'bell-3)       ; This does it

"*()+|{}[].? are ordinary but \" and \\ are special"

[^\n]         (list 'char)         ; Same thing as ‘.’
({letter}|_)({letter}|_|{digit})*  ; A C identifier
[][]                               ; One of the square brackets

Repe(ti){2}on   (list 'repetition)

^{letter}+:   (cons 'label yytext) ; A label placed at the
                                   ; beginning of the line
$^                                 ; No special meaning
<<EOF>>       (list 'eof)          ; Detection of the end of file
<<ERROR>>     (my-error)           ; Error handling