Add ScopeError stub

resolver/src/bundle.ts

@@ -3,10 +3,11 @@ import {Scope} from "./scope";
 import {Value, NoneValue} from "./value";
 import {Message} from "./message";
 import {hello, exclamation, select} from "./fixtures";
+import {ScopeError} from "./error";
 
 export interface Formatted {
     readonly value: string | null;
-    readonly errors: Array<string>;
+    readonly errors: Array<ScopeError>;
 }
 
 export class Bundle {

resolver/src/error.ts

@@ -0,0 +1,16 @@
+export enum ErrorKind {
+    UnknownVariable,
+    UnknownMessage,
+    MissingValue,
+}
+
+export class ScopeError extends Error {
+    public kind: ErrorKind;
+    public arg: string;
+
+    constructor(kind: ErrorKind, arg: string) {
+        super();
+        this.kind = kind;
+        this.arg = arg;
+    }
+}

resolver/src/message.ts

@@ -2,6 +2,7 @@ import * as ast from "./ast";
 import {Scope} from "./scope";
 import {Failure, Result} from "./result";
 import {Value, StringValue} from "./value";
+import {ScopeError, ErrorKind} from "./error";
 
 export class Message {
     private readonly id: string;
@@ -16,7 +17,7 @@ export class Message {
         if (this.value !== null) {
             return scope.resolvePattern(this.value);
         } else {
-            scope.errors.push(`Message ${this.id} has a null value.`);
+            scope.errors.push(new ScopeError(ErrorKind.MissingValue, this.id));
             return new Failure(new StringValue(this.id));
         }
     }

resolver/src/scope.ts

@@ -2,11 +2,12 @@ import * as ast from "./ast";
 import {Message} from "./message";
 import {Value, StringValue} from "./value";
 import {Result, Success, Failure} from "./result";
+import {ScopeError, ErrorKind} from "./error";
 
 export class Scope {
     private readonly messages: Map<string, Message>;
     private readonly variables: Map<string, Value>;
-    public errors: Array<string>;
+    public errors: Array<ScopeError>;
 
     constructor(messages: Map<string, Message>, variables: Map<string, Value>) {
         this.messages = messages;
@@ -32,7 +33,7 @@ export class Scope {
         if (value !== undefined) {
             return new Success(value);
         } else {
-            this.errors.push(`Unknown variable: $${node.id.name}.`);
+            this.errors.push(new ScopeError(ErrorKind.UnknownVariable, node.id.name));
             return new Failure(new StringValue(`$${node.id.name}`));
         }
     }
@@ -42,7 +43,7 @@ export class Scope {
         if (message !== undefined) {
             return message.resolveValue(this);
         } else {
-            this.errors.push(`Unknown message: ${node.id.name}.`);
+            this.errors.push(new ScopeError(ErrorKind.UnknownMessage, node.id.name));
             return new Failure(new StringValue(`${node.id.name}`));
         }
     }