sketch out backslash escape handling

src/parser2.ts

@@ -189,11 +189,53 @@ class Parser {
         case "]":
           return wip.finishScript();
 
+        case "backslash": {
+          this.advance();
+          const [type, chars, pos] = this.next;
+          switch (type) {
+            case "newline":
+              wip.finishWord();
+              break;
+
+            case "whitespace":
+            case "semicolon":
+            case "{":
+            case "}":
+            case "[":
+            case "]":
+            case "quote":
+            case "backslash":
+            case "comment":
+              wip.addWordPiece({ text: chars });
+              break;
+            case "text":
+              switch (chars) {
+                case "n":
+                  wip.addWordPiece({ text: "\n" });
+                  break;
+                default:
+                  throw new Error(`Unknown backslash escape: ${chars}`);
+              }
+              break;
+            case "EOF":
+              throw new Error(
+                "Reached end of input while parsing a backslash escape"
+              );
+            case "ERROR":
+              throw new Error(chars);
+            default:
+              throw new Error(
+                `Unhandled case: ${type satisfies never} (${chars})`
+              );
+          }
+          break;
+        }
+
         case "quote":
-        case "backslash":
         case "comment":
-        case "ERROR":
           throw new Error(`Unhandled case: ${type} (${chars})`);
+        case "ERROR":
+          throw new Error(chars);
         default:
           throw new Error(`Unhandled case: ${type satisfies never} (${chars})`);
       }