##Dijsktra's SSSP Algorithm
Graphs are being read from an adjacency list into a cyclic linked list of nodes.
The dijkstra function serves as a wrapper around linking the data structure and the actual graph traversal.
The traverse function poses the only significant difference between the versions:
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fold folds the list of nodes with the candidate and visited set as the aggegator.
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ioref uses mutable IORefs for the candidate and visited set.
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rec uses a non-monadic, recursive function to traverse the graph.
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state traverses the graph recursively using the State Monad.
##Todo