145 lines
6.2 KiB
Standard ML
145 lines
6.2 KiB
Standard ML
structure Cursor =
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struct
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(* Prerequisite: lineGap is moved to requested idx first
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* todo: check if we are in a \r\n pair, but this is not a priority *)
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fun viL (lineGap: LineGap.t, cursorIdx) =
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let
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val {rightStrings, idx = bufferIdx, ...} = lineGap
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in
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case rightStrings of
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hd :: tl =>
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let
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(* convert absolute cursorIdx to idx relative to hd string *)
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val strIdx = cursorIdx - bufferIdx
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in
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if strIdx + 1 < String.size hd then
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(* if there is at least one character after this idx *)
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let
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val nextChr = String.sub (hd, strIdx + 1)
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in
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(case nextChr of
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#"\n" =>
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if strIdx + 2 < String.size hd then
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(* if there are at least two chars after strIdx *)
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cursorIdx + 2
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else
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(* only one char after strIdx which is \n
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* if there is a string at the tl, can increment by 2 *)
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(case tl of
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_ :: _ => cursorIdx + 2
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| [] => cursorIdx + 1)
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| _ => cursorIdx + 1)
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end
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else
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(* no chars after this idx; have to check tl *)
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(case tl of
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tlhd :: tltl =>
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(* if there is another string after current head, we can increment cursorIdx
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* however, first we need to check if next char is \n. *)
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let
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val nextChr = String.sub (tlhd, 0)
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in
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(case nextChr of
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#"\n" =>
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if String.size tlhd > 2 then
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(* if there is at least one character after \n
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* then increment cursorIdx by 2 *)
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cursorIdx + 2
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else
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(* this string only contains \n
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* but there is a small possibility tltl
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* contains another string.
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* If it does, we can increment cursorIdx by 2,
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* moving past newline.
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* If not, increment cursorIdx by 1,
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* landing on newline. *)
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(case tltl of
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_ :: _ => cursorIdx + 2
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| [] => cursorIdx + 1)
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| _ =>
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(* next char is not newline,
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* so we can just increment by 1 *)
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cursorIdx + 1)
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end
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| [] =>
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(* if there is no string after current head, return original cursorIdx *)
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cursorIdx)
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end
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| [] =>
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(* return original cursorIdx if there is nothing to the right *)
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cursorIdx
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end
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(* Prerequisite: lineGap is moved to requested idx first
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* Implementation is mostly the same as the viL function,
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* except we focus on decrementing instead,
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* and we examing leftStrings list instead of tail of rightStrings
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* if head of rightStrings is empty or does not have the idx we want.
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* todo: check if we are in a \r\n pair, but this is not a priority *)
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fun viH (lineGap: LineGap.t, cursorIdx) =
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let
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val {rightStrings, leftStrings, idx = bufferIdx, ...} = lineGap
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in
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case rightStrings of
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hd :: _ =>
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let
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(* convert absolute cursorIdx to idx relative to hd string *)
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val strIdx = cursorIdx - bufferIdx
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in
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if strIdx > 0 then
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(* if there is at least one char before this index *)
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let
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val prevChr = String.sub (hd, strIdx - 1)
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in
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(case prevChr of
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#"\n" =>
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if strIdx > 1 then
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(* if there are at least two chars before strIdx *)
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cursorIdx - 2
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else
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(* only one char before strIdx which is \n
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* if there is a string at the leftStrings, can decrement by 2 *)
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(case leftStrings of
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_ :: _ => cursorIdx - 2
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| [] => cursorIdx - 1)
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| _ => cursorIdx - 1)
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end
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else
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(* no chars before this idx; have to check leftStrings *)
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(case leftStrings of
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lHd :: lTl =>
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(* if there is another string after current head, we can increment cursorIdx
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* however, first we need to check if next char is \n. *)
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let
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val lastChr = String.sub (lHd, String.size lHd - 1)
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in
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(case lastChr of
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#"\n" =>
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if String.size lHd > 2 then
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(* if there is at least one character before \n
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* then decrement cursorIdx by 2 *)
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cursorIdx - 2
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else
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(* this string only contains \n
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* but there is a small possibility tltl
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* contains another string.
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* If it does, we can increment cursorIdx by 2,
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* moving past newline.
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* If not, increment cursorIdx by 1,
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* landing on newline. *)
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(case lTl of
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_ :: _ => cursorIdx - 2
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| [] => cursorIdx - 1)
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| _ =>
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(* next char is not newline,
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* so we can just decrement by 1 *)
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cursorIdx - 1)
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end
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| [] =>
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(* if there is no string after current head, return original cursorIdx *)
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cursorIdx)
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end
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| [] => cursorIdx
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end
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end
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