wren ng thornton wrote: http://www.haskell.org/pipermail/haskell-cafe/2009-November/068728.html

...use matrices/arrays rather than lists...

...even just using an unboxed array for the matrices will make it much faster to traverse through...

Matrix multiplication is the sequential order inner or outer product of the columns/rows of one matrix and rows/columns of 2nd matrix: http://en.wikipedia.org/wiki/Matrix_multiplication#Relationship_with_the_inn... Afaics, optimize matrix multiplication with lists. Random arrays incurs a huge performance penality in Haskell, unless you revert to non-lazy implementation, in which case you have voided multi-core speed ups for very large arrays (aren't ANNs huge matrices?).