[Haskell-cafe] Type-level Programming

Vincenz Syntactically syntactically.vincenz at gmail.com
Fri Jun 22 12:32:39 EDT 2007

Dear all,

Recently I was playing around with encoding matrices in the type-level
system.  Thereby one can enable the multiplication of matrices.  The general
idea (which can be read about at (
is that there is more than one way to multiplly a matrix.

Given two matrices A and B, with M and N dimensions:

a_1*...*a_m and b_1*...*b_n  then whenever the last L dimensions of A match
the first L dimensions of B, they can be multiplied to have a matrix of


What one does is a dot-product on those middle L dimensions.  This is what I
tried to do in the code in the blogpost.  However, I was unable to formulate
the constraints for the final multiplication class that does the actual
proper cross-multiplication.

Is this at all possible, or was I chasing ghosts?

Best regards,
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