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cl-lexer

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cl-lexerlanguageregex

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This project originally was written by Michael Parker more than 10 years ago and now seems abandoned.

This system provides a simple regexp-based lexer. With macro deflexer you can define a function which accepts a string and returns another function. This resulting function can be called to retrieve tokens.

Here is an example from the README:

POFTHEDAY> (deflexer test-lexer
             ("[0-9]+([.][0-9]+([Ee][0-9]+)?)"
              (return (values 'flt (num %0))))
             ("[0-9]+"
              (return (values 'int (int %0))))
             ("[:alpha:][:alnum:]*"
              (return (values 'name %0)))
             ("[:space:]+"))

POFTHEDAY> (defvar *func*
             (test-lexer "1.0 12 fred 10.23e3"))
*FUNC*
POFTHEDAY> (funcall *func*)
FLT
1.0 (100.0%)
POFTHEDAY> (funcall *func*)
INT
12 (4 bits, #xC, #o14, #b1100)
POFTHEDAY> (funcall *func*)
NAME
"fred"
POFTHEDAY> (funcall *func*)
FLT
10230.0

Lexing function consists of a number of patterns and a code to act on these patters. If code block calls return to return any value as a token.

Here is how we can make another lexer to parse natural text:

POFTHEDAY> (deflexer test-lexer
             ("[:punct:]"
              (return (list 'punctuation %0)))
             ("[:alpha:][:alnum:]*"
              (return (list 'word %0)))
             ("[:space:]+"))

POFTHEDAY> (loop with text = "Alice loves Bob, but Bob loves Lisp!"
                 with lexer = (test-lexer text)
                 for (type value) = (funcall lexer)
                   then (funcall lexer)
                 while type
                 do (format t "~A: ~A~%"
                            type
                            value))
WORD: Alice
WORD: loves
WORD: Bob
PUNCTUATION: ,
WORD: but
WORD: Bob
WORD: loves
WORD: Lisp
PUNCTUATION: !

Here is more useful example - a log parser:

POFTHEDAY> (defparameter *log-message*
             " <INFO> [2020-04-21 22:11:23] - Hello Lisp World!")

POFTHEDAY> (deflexer test-lexer
             ("^[:space:]*<(DEBUG|INFO|ERROR)>"
              (return (list 'level %1)))
             ("\\[(.*?)\\]"
              (return (list 'time
                            (chronicity:parse %1))))
             (" - (.*)"
              (return (list 'message
                            %1)))
             ("[:space:]+"))

POFTHEDAY> (loop with text = *log-message*
                 with lexer = (test-lexer text)
                 for (type value) = (funcall lexer)
                   then (funcall lexer)
                 while type
                 do (format t "~A: ~A~%"
                            type
                            value))
LEVEL: INFO
TIME: 2020-04-21T22:11:23.000000+03:00
MESSAGE: Hello Lisp World!

That is it for today!


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