Let $ABCD$ be a rhombus with angle $\angle A = 60^\circ$. Let $E$ be a point, different from $D$, on the line $AD$. The lines $CE$ and $AB$ intersect at $F$. The lines $DF$ and $BE$ intersect at $M$. Determine the angle $\angle BMD$ as a function of the position of $E$ on $AD.$
1. **Identify the given elements and properties:**
   - $ABCD$ is a rhombus with $\angle A = 60^\circ$.
   - $E$ is a point on the line $AD$ different from $D$.
   - $CE$ and $AB$ intersect at $F$.
   - $DF$ and $BE$ intersect at $M$.
   - We need to determine $\angle BMD$ as a function of the position of $E$ on $AD$.

2. **Use properties of the rhombus:**
   - Since $ABCD$ is a rhombus, all sides are equal, and opposite angles are equal.
   - $\angle A = 60^\circ$ implies $\angle C = 60^\circ$ because opposite angles in a rhombus are equal.
   - The other angles, $\angle B$ and $\angle D$, are $120^\circ$ each because the sum of angles in a quadrilateral is $360^\circ$.

3. **Consider the circumcircle of $\triangle BCD$:**
   - Let the circumcircle of $\triangle BCD$ intersect $EF$ again at $G$.
   - Since $\angle DCE = \angle DBC = 60^\circ = \angle DAB$, quadrilateral $DAFG$ is cyclic.

4. **Show that $EABG$ is cyclic:**
   - Similarly, $\angle EAB = \angle EGB = 60^\circ$, so quadrilateral $EABG$ is cyclic.

5. **Use the Radical Axis Theorem:**
   - The circumcircles of $DAB$, $BFG$, and $GED$ are concurrent at a point $N$.
   - By the Radical Axis Theorem, the radical axes of these circles are concurrent.
   - Therefore, $AD$, $BN$, and $FG$ are concurrent, implying $B$, $N$, and $E$ are collinear.
   - Similarly, $D$, $N$, and $F$ are collinear, so $N \equiv M$.

6. **Determine $\angle BMD$:**
   - Since $N \equiv M$, $\angle BMD = 180^\circ - \angle DAB$.
   - Given $\angle DAB = 60^\circ$, we have $\angle BMD = 180^\circ - 60^\circ = 120^\circ$.

Thus, $\angle BMD$ is independent of the position of $E$ on $AD$ and is always $120^\circ$.

The final answer is $\boxed{120^\circ}$.