Safe Haskell	Safe-Inferred
Language	Haskell2010

Data.Equality.Matching.Pattern

Description

Definition of Pattern for use in equality matching (Matching), where patterns are matched against the e-graph

Synopsis

data Pattern lang
- = NonVariablePattern (lang (Pattern lang))
- | VariablePattern Var
pat :: lang (Pattern lang) -> Pattern lang

Documentation

data Pattern lang Source #

A pattern can be either a variable or an non-variable expression of patterns.

A NonVariablePattern will only match an expression if the lang constructor matches an expression and all child patterns match the expression children. A VariablePattern matches any expression.

Example

The expression

expr :: Fix Sym
expr = BinOp Add (Sym "x") (Const 2.0) -- i.e. x + 2

Would be matched against the following patterns

pat1 :: Pattern Sym
pat1 = VariablePattern 1

pat2 :: Pattern Sym
pat2 = NonVariablePattern (BinOp Add (VariablePattern 1) (VariablePattern 2))

pat3 :: Pattern Sym
pat3 = NonVariablePattern (BinOp Add (VariablePattern 1) (NonVariablePattern (Const 2)))

But would not be matched against the following patterns

pat4 :: Pattern Sym
pat4 = NonVariablePattern (Const 5)

pat5 :: Pattern Sym
pat5 = NonVariablePattern (BinOp Add (NonVariablePattern (Sym "y")) (NonVariablePattern (Const 2)))

pat6 :: Pattern Sym
pat6 = NonVariablePattern (BinOp Add (NonVariablePattern (Sym "x")) (NonVariablePattern (Const 3)))

IsString

Pattern instances IsString, which means one can write a variable pattern simply as a string.

It works by using hashString to create a unique integer for a VariablePattern

For example, we could write the following pattern that would match a+a and b+b but not a+b

pat7 :: Pattern Sym
pat7 = pat (BinOp Add "x" "x")

Constructors

NonVariablePattern (lang (Pattern lang))
VariablePattern Var	Should be a >0 positive number

Instances

Instances details

IsString (Pattern lang) Source #
Instance details Defined in Data.Equality.Matching.Pattern Methods fromString :: String -> Pattern lang #
(forall a. Show a => Show (lang a)) => Show (Pattern lang) Source #
Instance details Defined in Data.Equality.Matching.Pattern Methods showsPrec :: Int -> Pattern lang -> ShowS # show :: Pattern lang -> String # showList :: [Pattern lang] -> ShowS #
(forall a. Eq a => Eq (l a)) => Eq (Pattern l) Source #
Instance details Defined in Data.Equality.Matching.Pattern Methods (==) :: Pattern l -> Pattern l -> Bool # (/=) :: Pattern l -> Pattern l -> Bool #
(forall a. Eq a => Eq (l a), forall a. Ord a => Ord (l a)) => Ord (Pattern l) Source #
Instance details Defined in Data.Equality.Matching.Pattern Methods compare :: Pattern l -> Pattern l -> Ordering # (<) :: Pattern l -> Pattern l -> Bool # (<=) :: Pattern l -> Pattern l -> Bool # (>) :: Pattern l -> Pattern l -> Bool # (>=) :: Pattern l -> Pattern l -> Bool # max :: Pattern l -> Pattern l -> Pattern l # min :: Pattern l -> Pattern l -> Pattern l #

pat :: lang (Pattern lang) -> Pattern lang Source #

Synonym for NonVariablePattern.

Example

pat8 :: Pattern Sym
pat8 = pat (BinOp Mul "y" (pat (Const 2))) -- matches any product of an expression by 2