Add support for erase left and erase line in term.ANSI

.release-notes/rfc75.md

@@ -0,0 +1,24 @@
+## Add support for erase left and erase line in term.ANSI
+
+We've implemented [RFC #75](https://github.com/ponylang/rfcs/blob/main/text/0075-ansi-erase.md) that set out a means of updating `ANSI` in the `term` package to support not just ANSI erase right, but also erase left, and erase line.
+
+Existing functionality continues to work as is. All existing erase right functionality will continue to work without breakage. The `erase` method has been augmented to take an option parameter for the direction to erase. `EraseRight` is the default, thus keeping existing behavior. `EraseLeft` and `EraseLine` options have been added as well.
+
+To erase left, one would do:
+
+```pony
+ANSI.erase(EraseLeft)
+```
+
+To erase right, you could do either of the following:
+
+```pony
+ANSI.erase()
+ANSI.erase(EraseRight)
+```
+
+And finally, to erase an entire line:
+
+```pony
+ANSI.erase(EraseLine)
+```

packages/term/ansi.pony

@@ -60,11 +60,19 @@ primitive ANSI
     """
     "\x1B[H\x1B[2J"
 
-  fun erase(): String =>
-    """
-    Erases everything to the right of the cursor on the line the cursor is on.
-    """
-    "\x1B[0K"
+  fun erase(direction: _EraseDirection = EraseRight): String =>
+    """
+    Erases content. The direction to erase is dictated by the `direction`
+    parameter. Use `EraseLeft` to erase everything from the cursor to the
+    beginning of the line. Use `EraseLine` to erase the entire line. Use
+    `EraseRight` to erase everything from the cursor to the end of the line.
+    The default direction is `EraseRight`.
+    """
+    match direction
+    | EraseRight => "\x1B[0K"
+    | EraseLeft => "\x1B[1K"
+    | EraseLine => "\x1B[2K"
+    end
 
   fun reset(): String =>
     """
@@ -287,3 +295,9 @@ primitive ANSI
     Bright grey background.
     """
     "\x1B[47m"
+
+primitive EraseLeft
+primitive EraseLine
+primitive EraseRight
+
+type _EraseDirection is (EraseLeft | EraseLine | EraseRight)