From: Olivier Georg <firstname.lastname@example.org> Subject: [mg5345] Argument types
> I recently discovered that you could specify the type of the > arguments of a function being defined. For example, f[x_Integer] > if you want x to be an integer. There's also List, Real, Complex > and Symbol. But there's also ?MatrixQ which is not in the > Mathematica book, to specify a matrix. Are there other types?
_h is matched by anything with head h; this can be explicit for example h, h,h[1,2,3]. Unfortunately, you can't see 3 in the form Integer, but you can find its head formally: