Tidy up error reporting

src/parser2.ts

@@ -35,6 +35,12 @@ export function parse(
 
 // Parser for evaluating Notcl scripts
 
+export class ParseError extends Error {
+  constructor(message: string, public pos: number) {
+    super(message);
+  }
+}
+
 type TokenType =
   | "newline"
   | "whitespace"
@@ -47,8 +53,7 @@ type TokenType =
   | "backslash"
   | "comment"
   | "text"
-  | "EOF"
+  | "EOF";
-  | "ERROR";
 
 type Token = [TokenType, string, number];
 
@@ -81,9 +86,9 @@ class WipScript {
     return this.wipWord.length == 0 && this.wipCommand.length == 0;
   }
 
-  addWordPiece(piece: InterpolatedPiece, pos?: number) {
+  addWordPiece(piece: InterpolatedPiece, pos: number) {
     if (this.endOfWordError) {
-      throw new Error(this.endOfWordError);
+      throw new ParseError(this.endOfWordError, pos);
     }
     if (this.startOfWord()) {
       this.wordPos = pos;
@@ -137,13 +142,14 @@ class Parser {
       }
     }
 
-    return (this.next = ["ERROR", "Token not matched", startPos]);
+    throw new ParseError("Token not matched", startPos);
   }
 
   expect(type: TokenType) {
     if (this.next[0] != type) {
-      throw new Error(
+      throw new ParseError(
-        `Expected ${type}, found ${this.next[0]} (${this.next[1]})`
+        `Expected ${type}, found ${this.next[0]} (${this.next[1]})`,
+        this.next[2]
       );
     }
   }
@@ -175,7 +181,7 @@ class Parser {
         case "[": {
           this.advance();
           const script = this.parseScript();
-          wip.addWordPiece({ script });
+          wip.addWordPiece({ script }, pos);
           this.expect("]");
           break;
         }
@@ -200,8 +206,6 @@ class Parser {
                 case "backslash":
                   this.advance();
                   continue;
-                case "ERROR":
-                  throw new Error(chars);
                 default:
                   continue;
               }
@@ -223,10 +227,11 @@ class Parser {
 
         case "quote":
           throw new Error(`Unhandled case: ${type} (${chars})`);
-        case "ERROR":
-          throw new Error(chars);
         default:
-          throw new Error(`Unhandled case: ${type satisfies never} (${chars})`);
+          throw new ParseError(
+            `Unhandled case: ${type satisfies never} (${chars})`,
+            pos
+          );
       }
 
       this.advance();
@@ -261,17 +266,19 @@ class Parser {
             wip.addWordPiece({ text: "\n" }, pos);
             break;
           default:
-            throw new Error(`Unknown backslash escape: ${chars}`);
+            throw new ParseError(`Unknown backslash escape: ${chars}`, pos);
         }
         break;
       case "EOF":
-        throw new Error(
+        throw new ParseError(
-          "Reached end of input while parsing a backslash escape"
+          "Reached end of input while parsing a backslash escape",
+          pos
         );
-      case "ERROR":
-        throw new Error(chars);
       default:
-        throw new Error(`Unhandled case: ${type satisfies never} (${chars})`);
+        throw new ParseError(
+          `Unhandled case: ${type satisfies never} (${chars})`,
+          pos
+        );
     }
   }
 
@@ -297,9 +304,10 @@ class Parser {
         case "}":
           return wip;
         case "EOF":
-          throw new Error("Reached end of input while parsing a brace word");
+          throw new ParseError(
-        case "ERROR":
+            "Reached end of input while parsing a brace word",
-          throw new Error(chars);
+            pos
+          );
         default:
           wip += chars;
       }