# obdd: Ordered Reduced Binary Decision Diagrams

[ library, logic ] [ Propose Tags ]

Construct, combine and query OBDDs; an efficient representation for formulas in propositional logic.

This is mostly educational. The BDDs do not share nodes (there is no persistent BDD base) and this might introduce inefficiencies.

An important (for me, in teaching) feature is that I can immediately draw the BDD to an X11 window (via graphviz). For example, to show the effect of different variable orderings, try this in ghci (type q to close the drawing windows).

import Prelude hiding (not,(&&),(||),and,or,any,all)
import OBDD
let f [] = false; f (x:y:zs) = x && y || f zs
display $f$ map variable [1,2,3,4,5,6]
display $f$ map variable [1,4,2,5,3,6]

OBDD implements Ersatz.Boolean which re-defines Boolean operations from the Prelude. The recommended way of using this is shown in the previous example.

If you want better performance, use a library with a persistent BDD base, e.g., CUDD Haskell bindings, see this example.

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