Implement SAVE-INPUT and RESTORE-INPUT

[pforth] / fth / save-input.fth

\ 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