scsh-0.6/scsh/fr.scm

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;;; Field and record parsing utilities for scsh.
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;;; Copyright (c) 1994 by Olin Shivers. See file COPYING.
;;; Notes:
;;; - Comment on the dependencies here...
;;; - Awk should deal with case-insensitivity.
;;; - Should I change the field-splitters to return lists? It's the
;;; right thing, and costs nothing in terms of efficiency.
;;; Looping primitives:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; It is nicer for loops that loop over a bunch of different things
;;; if you can encapsulate the idea of iterating over a data structure
;;; with a
;;; (next-element state) -> elt next-state
;;; (more-elements? state) -? #t/#f
;;; generator/termination-test pair. You can use the generator with REDUCE
;;; to make a list; you can stick it into a loop macro to loop over the
;;; elements. For example, if we had an extensible Yale-loop style loop macro,
;;; we could have a loop clause like
;;;
;;; (loop (for field in-infix-delimited-string ":" path)
;;; (do (display field) (newline)))
;;;
;;; and it would be simple to expand this into code using the generator.
;;; With procedural inlining, you can get pretty optimal loops over data
;;; structures this way.
;;;
;;; As of now, you are forced to parse fields into a buffer, and loop
;;; over that. This is inefficient of time and space. If I ever manage to do
;;; an extensible loop macro for Scheme 48, I'll have to come back to this
;;; package and rethink how to provide this functionality.
;;; Forward-progress guarantees and empty string matches.
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; A loop that pulls text off a string by matching a regexp against
;;; that string can conceivably get stuck in an infinite loop if the
;;; regexp matches the empty string. For example, the regexps
;;; ^, $, .*, foo|[^f]* can all match the empty string.
;;;
;;; The regexp-loop routines in this code are careful to handle this case.
;;; If a regexp matches the empty string, the next search starts, not from
;;; the end of the match (which in the empty string case is also the
;;; beginning -- there's the rub), but from the next character over.
;;; This is the correct behaviour. Regexps match the longest possible
;;; string at a given location, so if the regexp matched the empty string
;;; at location i, then it is guaranteed they could not have matched
;;; a longer pattern starting with character #i. So we can safely begin
;;; our search for the next match at char i+1.
;;;
;;; So every iteration through the loop makes some forward progress,
;;; and the loop is guaranteed to terminate.
;;;
;;; This has the effect you want with field parsing. For example, if you split
;;; a string with the empty pattern, you will explode the string into its
;;; individual characters:
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;;; ((suffix-splitter (rx "")) "foo") -> #("" "f" "o" "o")
;;; However, even though this boundary case is handled correctly, we don't
;;; recommend using it. Say what you mean -- just use a field splitter:
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;;; ((field-splitter (rx any)) "foo") -> #("f" "o" "o")
;;; FIELD PARSERS
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This section defines routines to split a string into fields.
;;; You can parse by specifying a pattern that *separates* fields,
;;; a pattern that *terminates* fields, or a pattern that *matches*
;;; fields.
(define (->delim-matcher x)
(if (procedure? x) x ; matcher proc
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(let ((re (cond ((string? x) (re-string x))
((char-set? x) (re-char-set x))
((char? x) (re-string (string x)))
((regexp? x) x)
(else (error "Illegal field-reader delimiter value" x)))))
(lambda (s i)
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(cond ((regexp-search re s i) =>
(lambda (m) (values (match:start m 0) (match:end m 0))))
(else (values #f #f)))))))
;;; (infix-splitter [re num-fields handle-delim]) -> parser
;;; (suffix-splitter [re num-fields handle-delim]) -> parser
;;; (sloppy-suffix-splitter [re num-fields handle-delim]) -> parser
;;; (field-splitter [re num-fields]) -> parser
;;;
;;; (parser string [start]) -> string-list
(define (make-field-parser-generator default-delim-matcher loop-proc)
;; This is the parser-generator
(lambda args
(let-optionals args ((delim-spec default-delim-matcher)
(num-fields #f)
(handle-delim 'trim))
;; Process and error-check the args
(let ((match-delim (->delim-matcher delim-spec))
(cons-field (case handle-delim ; Field is s[i,j).
((trim) ; Delimiter is s[j,k).
(lambda (s i j k fields)
(cons (substring s i j) fields)))
((split)
(lambda (s i j k fields)
(cons (substring s j k)
(cons (substring s i j) fields))))
((concat)
(lambda (s i j k fields)
(cons (substring s i k)
fields)))
(else
(error "Illegal handle-delim spec"
handle-delim)))))
(receive (num-fields nfields-exact?)
(cond ((not num-fields) (values #f #f))
((not (integer? num-fields))
(error "Illegal NUM-FIELDS value" num-fields))
((<= num-fields 0) (values (- num-fields) #f))
(else (values num-fields #t)))
;; This is the parser.
(lambda (s . maybe-start)
(reverse (loop-proc s (:optional maybe-start 0)
match-delim cons-field
num-fields nfields-exact?))))))))
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;;; Default field spec is runs of non-whitespace chars.
(define default-field-matcher (->delim-matcher (rx (+ (~ white)))))
;;; (field-splitter [field-spec num-fields])
(define (field-splitter . args)
(let-optionals args ((field-spec default-field-matcher)
(num-fields #f))
;; Process and error-check the args
(let ((match-field (->delim-matcher field-spec)))
(receive (num-fields nfields-exact?)
(cond ((not num-fields) (values #f #f))
((not (integer? num-fields))
(error "Illegal NUM-FIELDS value"
field-splitter num-fields))
((<= num-fields 0) (values (- num-fields) #f))
(else (values num-fields #t)))
;; This is the parser procedure.
(lambda (s . maybe-start)
(reverse (fieldspec-field-loop s (:optional maybe-start 0)
match-field num-fields nfields-exact?)))))))
;;; These four procedures implement the guts of each parser
;;; (field, infix, suffix, and sloppy-suffix).
;;;
;;; The CONS-FIELD argument is a procedure that parameterises the
;;; HANDLE-DELIM action for the field parser.
;;;
;;; The MATCH-DELIM argument is used to match a delimiter.
;;; (MATCH-DELIM S I) returns two integers [start, end] marking
;;; the next delimiter after index I in string S. If no delimiter is
;;; found, it returns [#f #f].
;;; In the main loop of each parser, the loop variable LAST-NULL? tells if the
;;; previous delimiter-match matched the empty string. If it did, we start our
;;; next delimiter search one character to the right of the match, so we won't
;;; loop forever. This means that an empty delimiter regexp "" simply splits
;;; the string at each character, which is the correct thing to do.
;;;
;;; These routines return the answer as a reversed list.
(define (fieldspec-field-loop s start match-field num-fields nfields-exact?)
(let ((end (string-length s)))
(let lp ((i start) (nfields 0) (fields '()) (last-null? #f))
(let ((j (if last-null? (+ i 1) i)) ; Where to start next delim search.
;; Check to see if we made our quota before returning answer.
(finish-up (lambda ()
(if (and num-fields (< nfields num-fields))
(error "Too few fields in record." num-fields s)
fields))))
(cond ((> j end) (finish-up)) ; We are done. Finish up.
;; Read too many fields. Bomb out.
((and nfields-exact? (> nfields num-fields))
(error "Too many fields in record." num-fields s))
;; Made our lower-bound quota. Quit early.
((and num-fields (= nfields num-fields) (not nfields-exact?))
(if (= i end) fields ; Special case hackery.
(cons (substring s i end) fields)))
;; Match off another field & loop.
(else (receive (m0 m1) (match-field s j)
(if m0 (lp m1 (+ nfields 1)
(cons (substring s m0 m1) fields)
(= m0 m1))
(finish-up))))))))) ; No more matches. Finish up.
(define (infix-field-loop s start match-delim cons-field
num-fields nfields-exact?)
(let ((end (string-length s)))
(if (= start end) '() ; Specially hack empty string.
(let lp ((i start) (nfields 0) (fields '()) (last-null? #f))
(let ((finish-up (lambda ()
;; s[i,end) is the last field. Terminate the loop.
(cond ((and num-fields (< (+ nfields 1) num-fields))
(error "Too few fields in record."
num-fields s))
((and nfields-exact?
(>= nfields num-fields))
(error "Too many fields in record."
num-fields s))
(else
(cons (substring s i end) fields)))))
(j (if last-null? (+ i 1) i))) ; Where to start next search.
(cond
;; If we've read NUM-FIELDS fields, quit early .
((and num-fields (= nfields num-fields))
(if nfields-exact?
(error "Too many fields in record." num-fields s)
(cons (substring s i end) fields)))
((<= j end) ; Match off another field.
(receive (m0 m1) (match-delim s j)
(if m0
(lp m1 (+ nfields 1)
(cons-field s i m0 m1 fields)
(= m0 m1))
(finish-up)))) ; No more delimiters - finish up.
;; We've run off the end of the string. This is a weird
;; boundary case occuring with empty-string delimiters.
(else (finish-up))))))))
;;; Match off an optional initial delimiter,
;;; then jump off to the suffix parser.
(define (sloppy-suffix-field-loop s start match-delim cons-field
num-fields nfields-exact?)
;; If sloppy-suffix, skip an initial delimiter if it's there.
(let ((start (receive (i j) (match-delim s start)
(if (and i (zero? i)) j start))))
(suffix-field-loop s start match-delim cons-field
num-fields nfields-exact?)))
(define (suffix-field-loop s start match-delim cons-field
num-fields nfields-exact?)
(let ((end (string-length s)))
(let lp ((i start) (nfields 0) (fields '()) (last-null? #f))
(let ((j (if last-null? (+ i 1) i))) ; Where to start next delim search.
(cond ((= i end) ; We are done.
(if (and num-fields (< nfields num-fields)) ; Didn't make quota.
(error "Too few fields in record." num-fields s)
fields))
;; Read too many fields. Bomb out.
((and nfields-exact? (= nfields num-fields))
(error "Too many fields in record." num-fields s))
;; Made our lower-bound quota. Quit early.
((and num-fields (= nfields num-fields) (not nfields-exact?))
(cons (substring s i end) fields))
(else ; Match off another field.
(receive (m0 m1) (match-delim s j)
(if m0 (lp m1 (+ nfields 1)
(cons-field s i m0 m1 fields)
(= m0 m1))
(error "Missing field terminator" s)))))))))
;;; Now, build the exported procedures: {infix,suffix,sloppy-suffix}-splitter.
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(define default-suffix-matcher (->delim-matcher (rx (| (+ white) eos))))
(define default-infix-matcher (->delim-matcher (rx (+ white))))
(define infix-splitter
(make-field-parser-generator default-infix-matcher infix-field-loop))
(define suffix-splitter
(make-field-parser-generator default-suffix-matcher suffix-field-loop))
(define sloppy-suffix-splitter
(make-field-parser-generator default-suffix-matcher sloppy-suffix-field-loop))
;;; Reading records
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define default-record-delims (char-set #\newline))
;;; (record-reader [delims elide? handle-delim]) -> reader
;;; (reader [port]) -> string or eof
(define (record-reader . args)
(let-optionals args ((delims default-record-delims)
(elide? #f)
(handle-delim 'trim))
(let ((delims (x->char-set delims)))
(case handle-delim
((trim) ; TRIM-delimiter reader.
(lambda maybe-port
(let ((s (apply read-delimited delims maybe-port)))
(if (and (not (eof-object? s)) elide?)
(apply skip-char-set delims maybe-port)) ; Snarf extra delims.
s)))
((concat) ; CONCAT-delimiter reader.
(let ((not-delims (char-set-complement delims)))
(lambda maybe-port
(let* ((p (:optional maybe-port (current-input-port)))
(s (read-delimited delims p 'concat)))
(if (or (not elide?) (eof-object? s)) s
(let ((extra-delims (read-delimited not-delims p 'peek)))
(if (eof-object? extra-delims) s
(string-append s extra-delims))))))))
((split) ; SPLIT-delimiter reader.
(let ((not-delims (char-set-complement delims)))
(lambda maybe-port
(let ((p (:optional maybe-port (current-input-port))))
(receive (s delim) (read-delimited delims p 'split)
(if (eof-object? s) (values s s)
(values s
(if (or (not elide?) (eof-object? delim))
delim
;; Elide: slurp in extra delims.
(let ((delim (string delim))
(extras (read-delimited not-delims
p 'peek)))
(if (eof-object? extras) delim
(string-append delim extras)))))))))))
(else
(error "Illegal delimiter-action" handle-delim))))))
;;; Reading and parsing records
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; (field-reader [field-parser rec-reader]) -> reader
;;; (reader [port]) -> [raw-record parsed-record] or [eof #()]
;;;
;;; This is the field reader, which is basically just a composition of
;;; RECORD-READER and FIELD-PARSER.
(define default-field-parser (field-splitter))
(define (field-reader . args)
(let-optionals args ((parser default-field-parser)
(rec-reader read-line))
(lambda maybe-port
(let ((record (apply rec-reader maybe-port)))
(if (eof-object? record)
(values record '#())
(values record (parser record)))))))
;;; Parse fields by regexp
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; This code parses up a record into fields by matching a regexp specifying
;;; the field against the record. The regexp describes the *field*. In the
;;; other routines, the regexp describes the *delimiters*. They are
;;; complimentary.
;;; Repeatedly do (APPLY PROC M STATE) to generate new state values,
;;; where M is a regexp match structure made from matching against STRING.
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;(define (regexp-fold string start regexp proc . state)
; (let ((end (string-length string)))
; (let lp ((i start) (state state) (last-null? #f))
; (let ((j (if last-null? (+ i 1) i)))
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; (cond ((and (<= j end) (regexp-search regexp string j)) =>
; (lambda (m)
; (receive state (apply proc m state)
; (lp (match:end m) state (= (match:start m) (match:end m))))))
; (else (apply values state)))))))
;
;(define (all-regexp-matches regexp string)
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; (reverse (regexp-fold string 0 regexp
; (lambda (m ans) (cons (match:substring m 0) ans))
; '())))