Parser throws error when defining a function in a multiline expression

The following works fine:

``` js
var scope = {};
math.eval('f(x) = x^2', scope);
scope.f(3); // 9
```

but when having a multiline expression containing a function definition, we get an error:

``` js
var scope = {};
math.eval('a=2; f(x) = x^a', scope);  
    // Uncaught SyntaxError: missing ) after argument list
```
