Improved the SyntaxError exeptions thrown by the Parser

examples/input-after-end-error.egg

@@ -0,0 +1,4 @@
+do(
+  define(x, 3),
+  print(x)
+) moreinput

lib/parse.js

@@ -25,7 +25,7 @@ class Parser {
     const result = this.parseExpression();
 
     if(this.lookahead !== null) {
-      throw new SyntaxError(`Unexpected input after the end of parsing`);
+      throw this._parserSyntaxError("Unexpected input after the end of file.");
     }
 
     return result;
@@ -49,6 +49,9 @@ class Parser {
       let expr = {type: 'word', name: this.lookahead.value };
 
       return this.parseApply(expr);
+
+    } else {
+      throw this._parserSyntaxError("Unrecognized token while parsing the expression.");
     }
   }
 
@@ -76,9 +79,10 @@ class Parser {
 
       if(!this.lookahead || (this.lookahead.type !== 'COMMA' &&
         this.lookahead.type !== 'RP')) {
-        throw new SyntaxError(`Missing , or )`);
+        throw this._parserSyntaxError(`Missing , or ) after the expression`);
       }
 
+      // Don't consume RPs as argument tokens
       if(this.lookahead && this.lookahead.type !== 'RP') {
         this.lookahead = this.getToken();
       }
@@ -128,6 +132,13 @@ class Parser {
     tokenRegex.WHITES.lastIndex = this.lastIndex;
     tokenRegex.NEWLINE.lastIndex = this.lastIndex;
   }
+
+  _parserSyntaxError(message) {
+    let start = (this.lookahead) ? this.lookahead.start : this.lastIndex;
+
+    return new SyntaxError(`Parser::Line ${this.line}::Col ${start}\n${message}\n${this.program.slice(start-1, start + 10)}`);
+  }
+
 }
 
 Parser.TOKENS = [tokenRegex.NUMBER, tokenRegex.STRING, tokenRegex.WORD,