[Mesorah] verb + its infinitive

[Michael Hamm]

Achare d'rishas sh'lom'chem hatov.

First of all, much mazal tov to list member R' Ben Kandel in his new marriage.

I know I frequently bug you all with grammar questions, so this time I
asked at mi.yodeya.com first, but, not receiving a satisfactory reply
there, I'm bugging you yet again.

Is there any Jewish source, preferably among the rishonim, that
explains the meaning (p'shat, not d'rasha) of the duplication of a
verb by its infinitive, which appears so often, first in B'reshis 2:16
("achol tochel")?  Of course, it's generally translated as providing
emphasis, but does anyone know of an early Jewish source for this?

Michael Hamm
Postdoctoral Research Scholar
Department of Psychiatry
Washington University in St. Louis
St. Louis, Mo. 63110
msh210 at gmail.com