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212 lines
7.6 KiB
Scheme
212 lines
7.6 KiB
Scheme
(module lex mzscheme
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;; Provides the syntax used to create lexers and the functions needed to
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;; create and use the buffer that the lexer reads from. See doc.txt.
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(require-for-syntax "private-lex/generate-code.ss"
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"private-lex/structs.ss")
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(require (lib "readerr.ss" "syntax")
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"private-lex/token.ss")
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(provide lexer lexer-src-pos define-lex-abbrev define-lex-abbrevs
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make-lex-buf
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get-position position-offset position-line position-col position?
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define-tokens define-empty-tokens)
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(define-syntaxes (lexer lexer-src-pos)
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(let ((build-lexer
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(lambda (wrap)
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(lambda (stx)
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(syntax-case stx ()
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((_)
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(raise-syntax-error #f "empty lexer is not allowed" stx))
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((_ re-act ...)
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(begin
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(for-each
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(lambda (x)
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(syntax-case x ()
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((re act) (void))
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(_ (raise-syntax-error 'lexer
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"expects regular expression / action pairs"
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x))))
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(syntax->list (syntax (re-act ...))))
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(let ((table (generate-table (syntax (re-act ...)) stx)))
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(with-syntax ((start-state `,(table-start table))
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(trans-table `,(table-trans table))
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(eof-table `,(table-eof table))
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(no-lookahead `,(table-no-lookahead table))
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(actions `(vector ,@(vector->list (table-actions table)))))
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(syntax (lambda (lb)
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(lexer-body lb start-state trans-table eof-table actions no-lookahead wrap))))))))))))
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(values
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(build-lexer (lambda (x) x))
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(build-lexer (lambda (x fp ep) (list x fp ep))))))
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(define-syntax (define-lex-abbrev stx)
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(syntax-case stx ()
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((_ name re)
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(syntax
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(define-syntax name
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(make-lex-abbrev (quote-syntax re)))))
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(_
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(raise-syntax-error
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#f
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"Form should be (define-lex-abbrev name re)"
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stx))))
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(define-syntax (define-lex-abbrevs stx)
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(syntax-case stx ()
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((_ x ...)
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(let* ((abbrev (syntax->list (syntax (x ...))))
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(r (map (lambda (a)
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(syntax-case a ()
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((name re)
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(identifier? (syntax name))
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(syntax (define-lex-abbrev name re)))
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(_ (raise-syntax-error
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'Lexer-abbreviation
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"Form should be (identifier value)"
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a))))
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abbrev)))
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(datum->syntax-object
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#'here
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(cons 'begin r)
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stx)))
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(_
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(raise-syntax-error
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#f
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"Form should be (define-lex-abbrevs (name re) ...)"
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stx))))
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(define (lexer-body lb start-state trans-table eof-table actions no-lookahead wrap)
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(unless (lex-buffer? lb)
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(raise-type-error
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'lexer
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"lex-buf"
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0
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lb))
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(let ((first-pos (get-position lb)))
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(let lexer-loop (
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;; current-state
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(state start-state)
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;; the character to transition on
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(char (next-char lb))
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;; action for the longest match seen thus far
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;; including a match at the current state
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(longest-match-action
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(vector-ref actions start-state))
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;; how many characters have been read
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;; including the one just read
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(length 1)
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;; how many characters are in the longest match
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(longest-match-length 0))
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(let ((next-state
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(cond
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((eof-object? char)
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(vector-ref eof-table state))
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(else
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(vector-ref
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trans-table
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(bitwise-ior (char->integer char)
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(arithmetic-shift state 8)))))))
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(cond
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((not next-state)
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(do-match lb first-pos longest-match-length longest-match-action wrap))
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((vector-ref no-lookahead next-state)
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(let ((act (vector-ref actions next-state)))
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(do-match lb
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first-pos
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(if act length longest-match-length)
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(if act act longest-match-action)
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wrap)))
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(else
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(let ((act (vector-ref actions next-state)))
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(lexer-loop next-state
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(next-char lb)
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(if act
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act
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longest-match-action)
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(add1 length)
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(if act
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length
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longest-match-length)))))))))
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(define (do-match lb first-pos longest-match-length longest-match-action wrap)
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(let* ((match (get-match lb longest-match-length))
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(end-pos (get-position lb)))
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(if (not longest-match-action)
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(raise-read-error
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(format "lexer: No match found in input starting with: ~a" match)
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#f
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(position-line first-pos)
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(position-col first-pos)
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(position-offset first-pos)
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(- (position-offset end-pos) (position-offset first-pos))))
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(let/ec ret
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(wrap
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(longest-match-action
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(lambda () first-pos)
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(lambda () end-pos)
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(lambda () match)
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ret
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lb)))))
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;; Lex buffer is NOT thread safe
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;; c = char | eof
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;; lex-buf =
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;; (make-lex-buffer input-port int int int int)
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(define-struct lex-buffer (ip peek-amt line-start col-start offset-start))
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;; make-lex-buf: input-port -> lex-buf
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(define make-lex-buf
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(case-lambda
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((ip)
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(cond
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((not (input-port? ip))
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(raise-type-error 'make-lex-buf "input-port" 0 ip))
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(else
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(make-lex-buffer ip 0 0 0 0))))
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((ip offsets)
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(cond
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((not (input-port? ip))
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(raise-type-error 'make-lex-buf "input-port" 0 ip offsets))
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((or (not (= 3 (length offsets)))
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(not (andmap integer? offsets))
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(not (andmap exact? offsets))
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(not (andmap (lambda (x) (>= x 0)) offsets)))
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(raise-type-error 'make-lex-buf "list of 3 non-negative exact integers" 1 ip offsets))
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(else
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(make-lex-buffer ip 0 (car offsets) (cadr offsets) (caddr offsets)))))))
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(define (next-char lb)
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(let ((str (peek-string 1 (lex-buffer-peek-amt lb) (lex-buffer-ip lb))))
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(cond
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((string? str)
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(set-lex-buffer-peek-amt! lb (add1 (lex-buffer-peek-amt lb)))
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(string-ref str 0))
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(else eof))))
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;; get-match: lex-buf * int -> string
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;; reads the next i characters.
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(define (get-match lb i)
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(set-lex-buffer-peek-amt! lb 0)
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(read-string i (lex-buffer-ip lb)))
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(define-struct position (offset line col))
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(define (get-position lb)
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(let-values (((line col off) (port-next-location (lex-buffer-ip lb))))
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(if (and line col)
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(make-position (+ (lex-buffer-offset-start lb) off)
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(+ (lex-buffer-line-start lb) line)
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(if (= line 1)
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(+ (lex-buffer-col-start lb) col)
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col))
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(make-position (+ (lex-buffer-offset-start lb) off) #f #f))))
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)
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