Intensional logic is a family of mathematical formal systems that allow expressions whose value depends on hidden context or indices.

Streams are considered an intensional mapping, in the sense that neither the source nor the destination need be aware of the "hidden" destination coordinates. Each merely produces/consumes a one dimensional stream of data to be mapped by whatever stream implementation using "hidden" state (coordinates) to direct the mapping.

One of the best introductions is Multidimensional Programming, by E. A. Ashcroft, A. A. Faustini, R. Jagannathan, and W. W. Wadge, Oxford Univ. Press, New York, 1995.

In it, they cite the following paper as being the first realization that the Lucid programming language was intensional:

A.A. Faustini, and W.W. Wadge, "Intensional Programming". In J.C. Boudreaux, B. W. Hamill, and R. Jernigan, eds., The Role of Languages in Problem Solving 2 , Elsevier Science Pubs. B.V. (North Holland), 1987.

The web site at http://www.csl.sri.com/ip.html is also a good starting point. It links information and some papers from ISLIP, an annual symposium on languages for intensional programming.