I'm learning F# and I've decided to solve Project Euler's problem #81 with Dijkstra's algorithm, in F#.

This is the problem.

Is there any obvious mistake, inefficiency, any obvious possible improvement, any non-idiomatic use of the F# language?

I'm learning F# and I've decided to solve Project Euler's Problem #81 with Dijkstra's algorithm.

In the 5 by 5 matrix below, the minimal path sum from the top left to the bottom right, by only moving to the right and down, is indicated in bold red and is equal to 2427.

131   673 234 103 18
201   96  342 965 150
630   803 746 422 111
537   699 497 121 956
805   732 524 37  331

Find the minimal path sum, in matrix.txt (right click and 'Save Link/Target As...'), a 31K text file containing a 80 by 80 matrix, from the top left to the bottom right by only moving right and down.

Are there any obvious mistakes, inefficiency, any obvious possible improvements, any non-idiomatic use of the F# language?

This is the problem:

http://projecteuler.net/problem=81

This is the problem.