Re: [Phix Tutorial] Basic Sequence Actions
- Posted by _tom (admin) Jan 27, 2019
- 1553 views
_tom, can you explain the usage of a "gap?"
I've seen gaps like [2..1], but can there be other gaps, like [4..2]? And what does that do?
Gap | Item | Slice ( Caret | Cursor )
In a classic text based word processor a cursor "selects by highlighting a block on top of a character." In graphical word processors a caret "selects by a vertical line marker just before a character."
sequence s = "1234" -- a string with four digit characters
"1❷34" -- cursor "on 2"
"1|234" -- caret "before 2"
In a sequence|string we can use these ideas. In "1❷34" we say s[2] is the item 2 . In "1❷34" we say s[2..2] is the slice {2} . In "1|234" we say s[2..1] is the gap {} .
We can identify all gaps in a sequence as "|●|●|●|●|" ; there is a gap at the head and tail of a sequence; there is a gap between any two items. All gaps are an empty sequence {} or "" .
There is no item [0] or item [5] in the four item sequence "●●●●" , but there are lots of gaps.
| Gaps in a Sequence or String | ? | |
|---|---|---|
| s = "|◍○○○" | s = s[1..0] | "" |
| s = "○|◍○○" | s = s[2..1] | "" |
| s = "○○|◍○" | s = s[3..2] | "" |
| s = "○○○|◍" | s = s[4..3] | "" |
| s = "○○○○|" | s = s[5..4] | "" |
Each gap is an empty sequence.
To assign an atom to an empty gap is futile-- nothing happens.
An assignment will replace an empty gap with a new slice--the sequence grows by the length of the slice.
Reminder: This is a Phix tutorial. In oE you can not assign to a gap because the length of {} is zero and the length of anything interesting is >0 . In oE assignments must have equal lengths.
_tom
