| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Data.Equality.Analysis
Description
E-class analysis, which allows the concise expression of a program analysis over the e-graph.
An e-class analysis resembles abstract interpretation lifted to the e-graph level, attaching analysis data from a semilattice to each e-class.
The e-graph maintains and propagates this data as e-classes get merged and new e-nodes are added.
Analysis data can be used directly to modify the e-graph, to inform how or if rewrites apply their right-hand sides, or to determine the cost of terms during the extraction process.
References: https://arxiv.org/pdf/2004.03082.pdf
Documentation
class Eq domain => Analysis domain (l :: Type -> Type) where Source #
An e-class analysis with domain domain defined for a language l.
The domain is the type of the domain of the e-class analysis, that is, the
type of the data stored in an e-class according to this e-class analysis
Methods
makeA :: l domain -> domain Source #
When a new e-node is added into a new, singleton e-class, construct a new value of the domain to be associated with the new e-class, by accessing the associated data of the node's children
The argument is the e-node term populated with its children data
Example
-- domain = Maybe Double
makeA :: Expr (Maybe Double) -> Maybe Double
makeA = case
BinOp Div e1 e2 -> liftA2 (/) e1 e2
BinOp Sub e1 e2 -> liftA2 (-) e1 e2
BinOp Mul e1 e2 -> liftA2 (*) e1 e2
BinOp Add e1 e2 -> liftA2 (+) e1 e2
Const x -> Just x
Sym _ -> Nothing
joinA :: domain -> domain -> domain Source #
When e-classes c1 c2 are being merged into c, join d_c1 and d_c2 into a new value d_c to be associated with the new e-class c
modifyA :: EClass domain l -> (EClass domain l, [Fix l]) Source #
Optionally modify the e-class c (based on d_c), typically by adding an e-node to c. Modify should be idempotent if no other changes occur to the e-class, i.e., modify(modify(c)) = modify(c)
The return value of the modify function is both the modified class and the expressions (in their fixed-point form) to add to this class. We can't manually add them because not only would it skip some of the internal steps of representing + merging, but also because it's impossible to add any expression with depth > 0 without access to the e-graph (since we must represent every sub-expression in the e-graph first).
That's why we must return the modified class and the expressions to add to this class.
Example
Pruning an e-class with a constant value of all its nodes except for the leaf values, and adding a constant value node
-- Prune all except leaf e-nodes
modifyA cl =
case cl^._data of
Nothing -> (cl, [])
Just d -> ((_nodes %~ S.filter (F.null .unNode)) cl, [Fix (Const d)])