diff --git a/lib/compiler/session.js b/lib/compiler/session.js
index 7a1a0da..222b355 100644
--- a/lib/compiler/session.js
+++ b/lib/compiler/session.js
@@ -3,9 +3,20 @@
 "use strict";
 
 const ast = require( "../ast" );
+const GrammarError = require( "../grammar-error" );
 const opcodes = require( "./opcodes" );
 const parser = require( "../parser" );
 
+function fatal( message, location ) {
+
+    if ( typeof location !== "undefined" )
+
+        throw new GrammarError( message, location );
+
+    throw new Error( message );
+
+}
+
 class Session {
 
     constructor( options ) {
@@ -19,6 +30,9 @@ class Session {
         this.visitor = options.visitor || ast.visitor;
 
         if ( typeof options.warn === "function" ) this.warn = options.warn;
+        if ( typeof options.error === "function" ) this.error = options.error;
+
+        Object.defineProperty( this, "fatal", { value: fatal } );
 
     }
 
@@ -34,7 +48,13 @@ class Session {
 
     }
 
-    warn( message, details ) {}
+    warn( message, location ) {}
+
+    error( message, location ) {
+
+        fatal( message, location );
+
+    }
 
 }