kiama.example.lambda2.LazySubst.scala Maven / Gradle / Ivy
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/*
* This file is part of Kiama.
*
* Copyright (C) 2009 Anthony M Sloane, Macquarie University.
*
* Kiama is free software: you can redistribute it and/or modify it under
* the terms of the GNU Lesser General Public License as published by the
* Free Software Foundation, either version 3 of the License, or (at your
* option) any later version.
*
* Kiama is distributed in the hope that it will be useful, but WITHOUT ANY
* WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
* more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with Kiama. (See files COPYING and COPYING.LESSER.) If not, see
* .
*/
package kiama.example.lambda2
/**
* Evaluation of lambda calculus using lazy evaluation with
* term-level substitution and arithmetic operations.
*/
trait LazySubst extends EagerSubst {
import AST._
/**
* Recursively try to lazily evaluate expressions in applied functions,
* the bodies of substitutions and the arguments of operations.
*/
override lazy val traverse : Strategy =
rule {
// In an application we need to traverse to just the function
case App (e1, e2) => App (eval (e1), e2)
// In a substitution we need to traverse to the bound expression
// as well as the body expression.
case Let (x, t, e1, e2) => Let (x, t, e1, eval (e2))
// In an operation we need to traverse to both sub-expressions.
case Opn (op, e1, e2) => Opn (op, eval (e1), eval (e2))
}
}
class LazySubstEvaluator extends LazySubst