Problem calling erf from lisp



Suppose I have defined the following functions in 'file.lisp'

(defun $g (x) (mfuncall '$exp (* x x)))
(defun $h (x) (mfuncall '$sin (* x x)))
(defun $f (x) (mfuncall '$erf (* x x)))

Now,

(%i2) load("file.lisp")$
(%i3) g(0.1);
(%o3)                          1.010050167084168
(%i4) h(0.1);
(%o4)                          .0099998333341667
(%i5) f(0.1);
(%o5)                              erf(0.01)
(%i6) %,numer;
(%o6)                              erf(0.01)

but what I expect is

(%i7) erf(0.01);
(%o7)                          .0112834155558496

how can I circumvent this (at least for me) strange behaviour and get the 
desired result when calling f ?

I need to make gaussian approximations in the new version of a probability 
distributions package I wrote some months ago and I need to call erf with the 
argument depending on the user input.

-- 
--------------------------
Mario Rodriguez Riotorto
www.biomates.net