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;;; Guile Emacs Lisp
;;; Copyright (C) 2009, 2010, 2013 Free Software Foundation, Inc.
;;;
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 3 of the License, or (at your option) any later version.
;;;
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free Software
;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Code:
(define-module (language elisp lexer)
#:use-module (ice-9 regex)
#:export (get-lexer get-lexer/1))
;;; This is the lexical analyzer for the elisp reader. It is
;;; hand-written instead of using some generator. I think this is the
;;; best solution because of all that fancy escape sequence handling and
;;; the like.
;;;
;;; Characters are handled internally as integers representing their
;;; code value. This is necessary because elisp allows a lot of fancy
;;; modifiers that set certain high-range bits and the resulting values
;;; would not fit into a real Scheme character range. Additionally,
;;; elisp wants characters as integers, so we just do the right thing...
;;;
;;; TODO: #@count comments
;;; Report an error from the lexer (that is, invalid input given).
(define (lexer-error port msg . args)
(apply error msg args))
;;; In a character, set a given bit. This is just some bit-wise or'ing
;;; on the characters integer code and converting back to character.
(define (set-char-bit chr bit)
(logior chr (ash 1 bit)))
;;; Check if a character equals some other. This is just like char=?
;;; except that the tested one could be EOF in which case it simply
;;; isn't equal.
(define (is-char? tested should-be)
(and (not (eof-object? tested))
(char=? tested should-be)))
;;; For a character (as integer code), find the real character it
;;; represents or #\nul if out of range. This is used to work with
;;; Scheme character functions like char-numeric?.
(define (real-character chr)
(if (< chr 256)
(integer->char chr)
#\nul))
;;; Return the control modified version of a character. This is not
;;; just setting a modifier bit, because ASCII conrol characters must be
;;; handled as such, and in elisp C-? is the delete character for
;;; historical reasons. Otherwise, we set bit 26.
(define (add-control chr)
(let ((real (real-character chr)))
(if (char-alphabetic? real)
(- (char->integer (char-upcase real)) (char->integer #\@))
(case real
((#\?) 127)
((#\@) 0)
(else (set-char-bit chr 26))))))
;;; Parse a charcode given in some base, basically octal or hexadecimal
;;; are needed. A requested number of digits can be given (#f means it
;;; does not matter and arbitrary many are allowed), and additionally
;;; early return allowed (if fewer valid digits are found). These
;;; options are all we need to handle the \u, \U, \x and \ddd (octal
;;; digits) escape sequences.
(define (charcode-escape port base digits early-return)
(let iterate ((result 0)
(procdigs 0))
(if (and digits (>= procdigs digits))
result
(let* ((cur (read-char port))
(value (cond
((char-numeric? cur)
(- (char->integer cur) (char->integer #\0)))
((char-alphabetic? cur)
(let ((code (- (char->integer (char-upcase cur))
(char->integer #\A))))
(if (< code 0)
#f
(+ code 10))))
(else #f)))
(valid (and value (< value base))))
(if (not valid)
(if (or (not digits) early-return)
(begin
(unread-char cur port)
result)
(lexer-error port
"invalid digit in escape-code"
base
cur))
(iterate (+ (* result base) value) (1+ procdigs)))))))
;;; Read a character and process escape-sequences when necessary. The
;;; special in-string argument defines if this character is part of a
;;; string literal or a single character literal, the difference being
;;; that in strings the meta modifier sets bit 7, while it is bit 27 for
;;; characters.
(define basic-escape-codes
'((#\a . 7)
(#\b . 8)
(#\t . 9)
(#\n . 10)
(#\v . 11)
(#\f . 12)
(#\r . 13)
(#\e . 27)
(#\s . 32)
(#\d . 127)))
(define (get-character port in-string)
(let ((meta-bits `((#\A . 22)
(#\s . 23)
(#\H . 24)
(#\S . 25)
(#\M . ,(if in-string 7 27))))
(cur (read-char port)))
(if (char=? cur #\\)
;; Handle an escape-sequence.
(let* ((escaped (read-char port))
(esc-code (assq-ref basic-escape-codes escaped))
(meta (assq-ref meta-bits escaped)))
(cond
;; Meta-check must be before esc-code check because \s- must
;; be recognized as the super-meta modifier if a - follows.
;; If not, it will be caught as \s -> space escape code.
((and meta (is-char? (peek-char port) #\-))
(if (not (char=? (read-char port) #\-))
(error "expected - after control sequence"))
(set-char-bit (get-character port in-string) meta))
;; One of the basic control character escape names?
(esc-code esc-code)
;; Handle \ddd octal code if it is one.
((and (char>=? escaped #\0) (char<? escaped #\8))
(begin
(unread-char escaped port)
(charcode-escape port 8 3 #t)))
;; Check for some escape-codes directly or otherwise use the
;; escaped character literally.
(else
(case escaped
((#\^) (add-control (get-character port in-string)))
((#\C)
(if (is-char? (peek-char port) #\-)
(begin
(if (not (char=? (read-char port) #\-))
(error "expected - after control sequence"))
(add-control (get-character port in-string)))
escaped))
((#\x) (charcode-escape port 16 #f #t))
((#\u) (charcode-escape port 16 4 #f))
((#\U) (charcode-escape port 16 8 #f))
(else (char->integer escaped))))))
;; No escape-sequence, just the literal character. But remember
;; to get the code instead!
(char->integer cur))))
;;; Read a symbol or number from a port until something follows that
;;; marks the start of a new token (like whitespace or parentheses).
;;; The data read is returned as a string for further conversion to the
;;; correct type, but we also return what this is
;;; (integer/float/symbol). If any escaped character is found, it must
;;; be a symbol. Otherwise we at the end check the result-string
;;; against regular expressions to determine if it is possibly an
;;; integer or a float.
(define integer-regex (make-regexp "^[+-]?[0-9]+\\.?$"))
(define float-regex
(make-regexp
"^[+-]?([0-9]+\\.?[0-9]*|[0-9]*\\.?[0-9]+)(e[+-]?[0-9]+)?$"))
;;; A dot is also allowed literally, only a single dort alone is parsed
;;; as the 'dot' terminal for dotted lists.
(define no-escape-punctuation (string->char-set "-+=*/_~!@$%^&:<>{}?."))
(define (get-symbol-or-number port)
(let iterate ((result-chars '())
(had-escape #f))
(let* ((c (read-char port))
(finish (lambda ()
(let ((result (list->string
(reverse result-chars))))
(values
(cond
((and (not had-escape)
(regexp-exec integer-regex result))
'integer)
((and (not had-escape)
(regexp-exec float-regex result))
'float)
(else 'symbol))
result))))
(need-no-escape? (lambda (c)
(or (char-numeric? c)
(char-alphabetic? c)
(char-set-contains?
no-escape-punctuation
c)))))
(cond
((eof-object? c) (finish))
((need-no-escape? c) (iterate (cons c result-chars) had-escape))
((char=? c #\\) (iterate (cons (read-char port) result-chars) #t))
(else
(unread-char c port)
(finish))))))
;;; Parse a circular structure marker without the leading # (which was
;;; already read and recognized), that is, a number as identifier and
;;; then either = or #.
(define (get-circular-marker port)
(call-with-values
(lambda ()
(let iterate ((result 0))
(let ((cur (read-char port)))
(if (char-numeric? cur)
(let ((val (- (char->integer cur) (char->integer #\0))))
(iterate (+ (* result 10) val)))
(values result cur)))))
(lambda (id type)
(case type
((#\#) `(circular-ref . ,id))
((#\=) `(circular-def . ,id))
(else (lexer-error port
"invalid circular marker character"
type))))))
;;; Main lexer routine, which is given a port and does look for the next
;;; token.
(define lexical-binding-regexp
(make-regexp
"-\\*-(|.*;)[ \t]*lexical-binding:[ \t]*([^;]*[^ \t;]).*-\\*-"))
(define (lex port)
(define (lexical-binding-value string)
(and=> (regexp-exec lexical-binding-regexp string)
(lambda (match)
(not (member (match:substring match 2) '("nil" "()"))))))
(let* ((return (let ((file (if (file-port? port)
(port-filename port)
#f))
(line (1+ (port-line port)))
(column (1+ (port-column port))))
(lambda (token value)
(let ((obj (cons token value)))
(set-source-property! obj 'filename file)
(set-source-property! obj 'line line)
(set-source-property! obj 'column column)
obj))))
;; Read afterwards so the source-properties are correct above
;; and actually point to the very character to be read.
(c (read-char port)))
(cond
;; End of input must be specially marked to the parser.
((eof-object? c) (return 'eof c))
;; Whitespace, just skip it.
((char-whitespace? c) (lex port))
;; The dot is only the one for dotted lists if followed by
;; whitespace. Otherwise it is considered part of a number of
;; symbol.
((and (char=? c #\.)
(char-whitespace? (peek-char port)))
(return 'dot #f))
;; Continue checking for literal character values.
(else
(case c
;; A line comment, skip until end-of-line is found.
((#\;)
(if (= (port-line port) 0)
(let iterate ((chars '()))
(let ((cur (read-char port)))
(if (or (eof-object? cur) (char=? cur #\newline))
(let ((string (list->string (reverse chars))))
(return 'set-lexical-binding-mode!
(lexical-binding-value string)))
(iterate (cons cur chars)))))
(let iterate ()
(let ((cur (read-char port)))
(if (or (eof-object? cur) (char=? cur #\newline))
(lex port)
(iterate))))))
;; A character literal.
((#\?)
(return 'character (get-character port #f)))
;; A literal string. This is mainly a sequence of characters
;; just as in the character literals, the only difference is
;; that escaped newline and space are to be completely ignored
;; and that meta-escapes set bit 7 rather than bit 27.
((#\")
(let iterate ((result-chars '()))
(let ((cur (read-char port)))
(case cur
((#\")
(return 'string (list->string (reverse result-chars))))
((#\\)
(let ((escaped (read-char port)))
(case escaped
((#\newline #\space)
(iterate result-chars))
(else
(unread-char escaped port)
(unread-char cur port)
(iterate
(cons (integer->char (get-character port #t))
result-chars))))))
(else (iterate (cons cur result-chars)))))))
((#\#)
(let ((c (read-char port)))
(case c
((#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9)
(unread-char c port)
(let ((mark (get-circular-marker port)))
(return (car mark) (cdr mark))))
((#\')
(return 'function #f))
((#\:)
(call-with-values
(lambda () (get-symbol-or-number port))
(lambda (type str)
(return 'symbol (make-symbol str))))))))
;; Parentheses and other special-meaning single characters.
((#\() (return 'paren-open #f))
((#\)) (return 'paren-close #f))
((#\[) (return 'square-open #f))
((#\]) (return 'square-close #f))
((#\') (return 'quote #f))
((#\`) (return 'backquote #f))
;; Unquote and unquote-splicing.
((#\,)
(if (is-char? (peek-char port) #\@)
(if (not (char=? (read-char port) #\@))
(error "expected @ in unquote-splicing")
(return 'unquote-splicing #f))
(return 'unquote #f)))
;; Remaining are numbers and symbols. Process input until next
;; whitespace is found, and see if it looks like a number
;; (float/integer) or symbol and return accordingly.
(else
(unread-char c port)
(call-with-values
(lambda () (get-symbol-or-number port))
(lambda (type str)
(case type
((symbol)
;; str could be empty if the first character is already
;; something not allowed in a symbol (and not escaped)!
;; Take care about that, it is an error because that
;; character should have been handled elsewhere or is
;; invalid in the input.
(if (zero? (string-length str))
(begin
;; Take it out so the REPL might not get into an
;; infinite loop with further reading attempts.
(read-char port)
(error "invalid character in input" c))
(return 'symbol (string->symbol str))))
((integer)
;; In elisp, something like "1." is an integer, while
;; string->number returns an inexact real. Thus we need
;; a conversion here, but it should always result in an
;; integer!
(return
'integer
(let ((num (inexact->exact (string->number str))))
(if (not (integer? num))
(error "expected integer" str num))
num)))
((float)
(return 'float (let ((num (string->number str)))
(if (exact? num)
(error "expected inexact float"
str
num))
num)))
(else (error "wrong number/symbol type" type)))))))))))
;;; Build a lexer thunk for a port. This is the exported routine which
;;; can be used to create a lexer for the parser to use.
(define (get-lexer port)
(lambda () (lex port)))
;;; Build a special lexer that will only read enough for one expression
;;; and then always return end-of-input. If we find one of the quotation
;;; stuff, one more expression is needed in any case.
(define (get-lexer/1 port)
(let ((lex (get-lexer port))
(finished #f)
(paren-level 0))
(lambda ()
(if finished
(cons 'eof ((@ (ice-9 binary-ports) eof-object)))
(let ((next (lex))
(quotation #f))
(case (car next)
((paren-open square-open)
(set! paren-level (1+ paren-level)))
((paren-close square-close)
(set! paren-level (1- paren-level)))
((quote backquote unquote unquote-splicing circular-def)
(set! quotation #t)))
(if (and (not quotation) (<= paren-level 0))
(set! finished #t))
next)))))
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