Backwards motions and deletions

src/cg/06-textEditor.cg

@@ -53,10 +53,46 @@ textEditor = name \
     pos = skipWhile (ch \ charKind ch == kind) lines row col;
     skipWhile (ch \ ch == " ") lines pos.row pos.col;
 
+  skipBack = pred line row col lines \
+    col < 0
+    | True \ (row > 0
+      | True \ (
+        prevLine = nth (row - 1) lines ~ unwrapOr "";
+        skipBack pred prevLine (row - 1) (len prevLine - 1) lines)
+      | False \ { row = 0, col = 0 - 1 })
+    | False \ (pred (nth col line ~ unwrapOr "")
+      | True \ skipBack pred line row (col - 1) lines
+      | False \ { row = row, col = col });
+
+  prevWordStart = lines row col \
+    # step back 1
+    c = col - 1;
+    r = row;
+    r2 = c < 0
+      | True \ r - 1
+      | False \ r;
+    c2 = c < 0
+      | True \ (max 0 (len (nth (r - 1) lines ~ unwrapOr "") - 1))
+      | False \ c;
+    # no prev line
+    r2 < 0
+      | True \ { row = 0, col = 0 }
+      | False \ (
+        line = nth r2 lines ~ unwrapOr "";
+        # skip spaces backward
+        pos = skipBack (ch \ ch == " ") line r2 c2 lines;
+        # skip same kind backward
+        kind = charKind (nth pos.col (nth pos.row lines ~ unwrapOr "") ~ unwrapOr " ");
+        pos2 = skipBack (ch \ charKind ch == kind) (nth pos.row lines ~ unwrapOr "") pos.row (pos.col - 1) lines;
+        # go 1 ahead
+        { row = pos2.row, col = pos2.col + 1 }
+      );
+
   resolveMotion = motion state \
     from = { row = state.cursorRow, col = state.cursorCol };
     to = motion
       | Word \ nextWordStart state.lines from.row from.col
+      | BackWord \ prevWordStart state.lines from.row from.col
       | WholeLine \ from;
     { from = from, to = to };
 
@@ -66,11 +102,10 @@ textEditor = name \
 
   deleteRange = state from to \
     line = nth from.row state.lines ~ unwrapOr "";
-    toCol = to.row > from.row
+    startCol = min from.col to.col;
-      | True \ len line
+    endCol = max from.col to.col;
-      | False \ to.col;
+    newLine = (slice line 0 startCol) & (slice line endCol (len line));
-    newLine = (slice line 0 from.col) & (slice line toCol (len line));
+    state.{ lines = updateAt from.row (_ \ newLine) state.lines, cursorCol = startCol };
-    state.{ lines = updateAt from.row (_ \ newLine) state.lines, cursorCol = from.col };
 
   applyOperator = operator motion state \
     target = resolveMotion motion state;
@@ -277,6 +312,9 @@ textEditor = name \
             | Key { key = "d" } \ (state.pending
               | Some Delete \ applyOperator Delete WholeLine state
               | _ \ { state = state.{ pending = Some Delete }, emit = [] })
+            | Key { key = "b" } \ (state.pending
+              | None \ withScroll { state = moveCursor (resolveMotion BackWord state) state, emit = [] }
+              | Some Delete \ withScroll (applyOperator Delete BackWord state))
             | Key { key = "w" } \ (state.pending
               | None \ withScroll { state = moveCursor (resolveMotion Word state) state, emit = [] }
               | Some Delete \ withScroll (applyOperator Delete Word state))