Futhark.IR.Traversals

Functions for generic traversals across Futhark syntax trees. The motivation for this module came from dissatisfaction with rewriting the same trivial tree recursions for every module. A possible alternative would be to use normal "Scrap your boilerplate"-techniques, but these are rejected for two reasons:

• They are too slow.
• More importantly, they do not tell you whether you have missed some cases.

Instead, this module defines various traversals of the Futhark syntax tree. The implementation is rather tedious, but the interface is easy to use.

A traversal of the Futhark syntax tree is expressed as a record of functions expressing the operations to be performed on the various types of nodes.

The Futhark.Transform.Rename module is a simple example of how to use this facility.

Mapping

data Mapper frep trep m

Express a monad mapping operation on a syntax node. Each element of this structure expresses the operation to be performed on a given child.

Constructors

Mapper

Fields

• mapOnSubExp :: SubExp -> m SubExp
• mapOnBody :: Scope trep -> Body frep -> m (Body trep)

  Most bodies are enclosed in a scope, which is passed along for convenience.

• mapOnVName :: VName -> m VName
• mapOnRetType :: RetType frep -> m (RetType trep)
• mapOnBranchType :: BranchType frep -> m (BranchType trep)
• mapOnFParam :: FParam frep -> m (FParam trep)
• mapOnLParam :: LParam frep -> m (LParam trep)
• mapOnOp :: Op frep -> m (Op trep)

identityMapper :: Monad m => Mapper rep rep m

A mapper that simply returns the tree verbatim.

mapExpM :: (Applicative m, Monad m) => Mapper frep trep m -> Exp frep -> m (Exp trep)

Map a monadic action across the immediate children of an expression. Importantly, the mapping does not descend recursively into subexpressions. The mapping is done left-to-right.

mapExp :: Mapper frep trep Identity -> Exp frep -> Exp trep

Like mapExpM, but in the Identity monad.

Walking

data Walker rep m

Express a monad expression on a syntax node. Each element of this structure expresses the action to be performed on a given child.

Constructors

Walker

Fields

• walkOnSubExp :: SubExp -> m ()
• walkOnBody :: Scope rep -> Body rep -> m ()
• walkOnVName :: VName -> m ()
• walkOnRetType :: RetType rep -> m ()
• walkOnBranchType :: BranchType rep -> m ()
• walkOnFParam :: FParam rep -> m ()
• walkOnLParam :: LParam rep -> m ()
• walkOnOp :: Op rep -> m ()

identityWalker :: Monad m => Walker rep m

A no-op traversal.

walkExpM :: Monad m => Walker rep m -> Exp rep -> m ()

As mapExpM, but do not construct a result AST.