[Haskell-cafe] Update2

Patrick M patrickm7860 at yahoo.co.uk
Sat Feb 19 18:58:31 CET 2011

Ok so I wrote and update function

           update :: Node -> [Node] 
It takes in a Node and returns a list of the Nodes
that result from assigning True to an unassigned atom in one case and False in the other (ie. a case
split). The list returned has two nodes as elements. One node  contains the formula
with an atom assigned True and the model updated with this assignment, and the other contains
the formula with the atom assigned False and the model updated to show this. The lists of unassigned
atoms of each node are also  updated accordingly. This function makes use  of an 
assign function to make the assignments. It also uses the chooseAtom function  to
select the literal to assign.
        update :: Node -> [Node]
        update (formula, (atoms, model)) = [(assign (chooseAtom atoms, True) formula, (remove (chooseAtom atoms) atoms, ((chooseAtom atoms,True)) `insert` model)) , (assign (chooseAtom atoms, False) formula, (remove (chooseAtom atoms) atoms, ((chooseAtom atoms, False) `insert` model)) )] 

Now I have to do the same thing but this time I must  implement a variable selection heuristic.this should replace the chooseAtom and I'm supposed to write a function update2 using it

        type Atom = String
        type Literal = (Bool,Atom)
        type Clause = [Literal]  
        type Formula = [Clause]
        type Model = [(Atom, Bool)]
        type Node = (Formula, ([Atom], Model))
       update2 :: Node -> [Node]
       update2 = undefined
So my question is how can I create a heurestic and to implement it into the update2 function ,that shoud behave identical to the update function ?

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