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read: block comments

This commit is contained in:
Peter McGoron 2024-09-22 00:46:41 -04:00
parent e109c255ad
commit 2e43f36471
1 changed files with 76 additions and 2 deletions
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78
read.scm
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@ -120,6 +120,18 @@
;;; ;;;;;;;;;;;;;;;;;;;;;;
;;; Readtable constructors
;;;
;;; Readtables are composed of a CHARMAP, which is a map from characters
;;; to actions, and a DEFAULT-ACTION, which is taken when there is no
;;; match in CHARMAP.
;;;
;;; An "action" is a procedure that takes four arguments:
;;;
;;; TABLE: The current table.
;;; CHAR: The character that was matched against the CHARMAP in TABLE.
;;; ACC: An arbitrary "accumulator" value that is different depending
;;; on the readtable in question.
;;; PORT: A port reader object.
;;; ;;;;;;;;;;;;;;;;;;;;;;
;;; (READTABLE:NEW DEFAULT-ACTION CHARMAP)
@ -167,7 +179,7 @@
functions)))
;;; ;;;;;;;;;;;;;;;;;;
;;; Default readtables
;;; Default actions
;;; ;;;;;;;;;;;;;;;;;;
;;; Return an error.
@ -208,6 +220,12 @@
(lambda (oldtable __ _ port)
(readtable:next newtable oldtable port))))
;;; Jump to a new readtable, reading the new character.
(define readtable:jump/next
(lambda (newtable)
(lambda (oldtable _ acc port)
(readtable:next newtable acc port))))
;;; ;;;;;;;;;;;;;;;;;
;;; Identifier reader
;;; ;;;;;;;;;;;;;;;;;
@ -359,16 +377,69 @@
port)))
;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Reader for datum that start with "#"
;;; Reader for stuff that start with "#"
;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(define readtable:vector
(lambda (_ __ toplevel port)
(list 'vector (readtable:read-proper-list toplevel port))))
;;; Block comment reader.
;;;
;;; The outermost block comment reader is passed the toplevel reader as
;;; ACC. When the outermost block is finished, it will tail-call ACC.
;;; (It is basically the continuation of the reader.)
;;;
;;; When a nested block comment is found, it is passed #F as ACC, which
;;; it will not call. It will return an unspecified value.
;;;
;;; Since the read tables are not procedures, references to other tables
;;; in the same LETREC declaration must be protected with explicit LAMBDAs.
;;; Macros could make this much easier to read.
(define readtable:block-comment
(letrec ((potential-end
(readtable:process
(readtable:empty/default
(lambda (this char acc port) (readtable:act
loop
char
acc
port)))
(list readtable:update #\#
(lambda (this char acc port)
(if acc
(readtable:next acc #f port))))))
(potential-start
(readtable:process
(readtable:empty/default
(lambda (this char acc port) (readtable:act
loop
char
acc
port)))
(list readtable:update #\|
(lambda (this char acc port)
(readtable:next loop #f port)
(readtable:next loop acc port)))))
(loop
(readtable:process
(readtable:empty/default readtable:skip)
(list readtable:update #\#
(lambda (this char acc port)
(readtable:next potential-start
acc
port)))
(list readtable:update #\|
(lambda (this char acc port)
(readtable:next potential-end
acc
port))))))
loop))
(define readtable:hash
(readtable:process
(readtable:empty/default (readtable:error "unimplemented"))
(list readtable:update #\| (readtable:jump/next readtable:block-comment))
(list readtable:update %bol readtable:vector)))
;;; ;;;;;;;;;;;;;;;;
@ -424,3 +495,6 @@
(read-all "( a . b )")
(read-all "( a .b . c)")
(read-all "#( a b y)")
(read-all "(x y #| this is a block\n comment\n |# z w)")
(read-all "#( a b #| this is a #| nested block |# comment|# z w)")
(read-all "#(a b #(c #|close#|comment|#|#y))")