kiama.example.lambda2.ParLazySubst.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

/**
 * Lazy evaluation of lambda calculus with parallel term-level substitution
 * and arithmetic operations.
 */
trait ParLazySubst extends ParEagerSubst {

    import AST._

    /**
     * Lazily evaluate within the expression then try to reduce the
     * expression itself, repeating until no change.
     */
    override lazy val evals : Strategy =
        attempt (traverse) <* attempt (lambda <* evals)

    /**
     * Recursively try to lazily evaluate expressions in applications
     * and operations, but not within lambdas or substitutions.
     */
    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 an operation we need to traverse to both sub-expressions.
            case Opn (op, e1, e2)   => Opn (op, eval (e1), eval (e2))

        }

}

class ParLazySubstEvaluator extends ParLazySubst