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/*
* File: fscan.r
* Contents: move, pos, tab.
*/
"move(i) - move &pos by i, return substring of &subject spanned."
" Reverses effects if resumed."
function{0,1+} move(i)
if !cnv:C_integer(i) then
runerr(101,i)
abstract {
return string
}
body {
register C_integer j;
C_integer oldpos;
/*
* Save old &pos. Local variable j holds &pos before the move.
*/
oldpos = j = k_pos;
/*
* If attempted move is past either end of the string, fail.
*/
if (i + j <= 0 || i + j > StrLen(k_subject) + 1)
fail;
/*
* Set new &pos.
*/
k_pos += i;
/*
* Make sure i >= 0.
*/
if (i < 0) {
j += i;
i = -i;
}
/*
* Suspend substring of &subject that was moved over.
*/
suspend string(i, StrLoc(k_subject) + j - 1);
/*
* If move is resumed, restore the old position and fail.
*/
if (oldpos > StrLen(k_subject) + 1)
runerr(205, kywd_pos);
else {
k_pos = oldpos;
}
fail;
}
end
"pos(i) - test if &pos is at position i in &subject."
function{0,1} pos(i)
if !cnv:C_integer(i) then
runerr(101, i)
abstract {
return integer
}
body {
/*
* Fail if &pos is not equivalent to i, return i otherwise.
*/
if ((i = cvpos(i, StrLen(k_subject))) != k_pos)
fail;
return C_integer i;
}
end
"tab(i) - set &pos to i, return substring of &subject spanned."
"Reverses effects if resumed."
function{0,1+} tab(i)
if !cnv:C_integer(i) then
runerr(101, i);
abstract {
return string
}
body {
C_integer j, t, oldpos;
/*
* Convert i to an absolute position.
*/
i = cvpos(i, StrLen(k_subject));
if (i == CvtFail)
fail;
/*
* Save old &pos. Local variable j holds &pos before the tab.
*/
oldpos = j = k_pos;
/*
* Set new &pos.
*/
k_pos = i;
/*
* Make i the length of the substring &subject[i:j]
*/
if (j > i) {
t = j;
j = i;
i = t - j;
}
else
i = i - j;
/*
* Suspend the portion of &subject that was tabbed over.
*/
suspend string(i, StrLoc(k_subject) + j - 1);
/*
* If tab is resumed, restore the old position and fail.
*/
if (oldpos > StrLen(k_subject) + 1)
runerr(205, kywd_pos);
else {
k_pos = oldpos;
}
fail;
}
end
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