Added modifiers head and tail (#159)

* Added modifiers head and tail

* Include selection

src/Types.ts

@@ -101,13 +101,21 @@ export interface MatchingPairSymbolModifier {
 export interface IdentityModifier {
   type: "identity";
 }
+export interface HeadModifier {
+  type: "head";
+}
+export interface TailModifier {
+  type: "tail";
+}
 
 export type Modifier =
   | SurroundingPairModifier
   | ContainingScopeModifier
   | SubpieceModifier
   | MatchingPairSymbolModifier
-  | IdentityModifier;
+  | IdentityModifier
+  | HeadModifier
+  | TailModifier;
 
 export type SelectionType =
   | "character"

src/processTargets.ts

@@ -348,6 +348,28 @@ function transformSelection(
           },
         },
       ];
+
+    case "head":
+    case "tail": {
+      let anchor: Position, active: Position;
+      if (modifier.type === "head") {
+        anchor = selection.selection.end;
+        active = new Position(selection.selection.start.line, 0);
+      } else {
+        anchor = selection.selection.start;
+        active = selection.editor.document.lineAt(selection.selection.end).range
+          .end;
+      }
+      return [
+        {
+          selection: update(selection, {
+            selection: () => new Selection(anchor, active),
+          }),
+          context: {},
+        },
+      ];
+    }
+
     case "matchingPairSymbol":
     case "surroundingPair":
       throw new Error("Not implemented");