+\ SAVE-INPUT and RESTORE-INPUT
+
+anew task-save-input.fth
+
+private{
+
+: save-buffer ( -- column source-id 2 ) >in @ source-id 2 ;
+
+: restore-column ( column -- flag )
+ source nip over < if drop true exit then
+ >in ! false
+;
+
+\ Return the file-position of the beginning of the current line in
+\ file SOURCE-ID. Assume that the current line is stored in SOURCE
+\ and that the current file-position is at an end-of-line (or
+\ end-of-file).
+: line-start-position ( -- ud )
+ source-id file-position throw
+ \ unless at end-of-file, subtract newline
+ source-id file-size throw 2over d= 0= if 1 s>d d- then
+ \ subtract line length
+ source nip s>d d-
+;
+
+: save-file ( column line filepos:ud source-id 5 -- )
+ >in @
+ source-line-number@
+ line-start-position
+ source-id
+ 5
+;
+
+: restore-file ( column line filepos:ud -- flag )
+ source-id reposition-file if 2drop true exit then
+ source-line-number!
+ refill 0= if drop true exit then
+ restore-column
+;
+
+: ndrop ( n*x n -- ) 0 ?do drop loop ;
+
+}private
+
+\ Source Stack
+\ EVALUATE >IN SourceID=(-1) 2
+\ keyboard >IN SourceID=(0) 2
+\ file >IN lineNumber filePos SourceID=(fileID) 5
+: SAVE-INPUT ( -- column {line filepos}? source-id n )
+ source-id case
+ -1 of save-buffer endof
+ 0 of save-buffer endof
+ drop save-file exit
+ endcase
+;
+
+: RESTORE-INPUT ( column {line filepos}? source-id n -- flag )
+ over source-id <> if ndrop true exit then
+ drop
+ case
+ -1 of restore-column endof
+ 0 of restore-column endof
+ drop restore-file exit
+ endcase
+;
+
+privatize