kmath/kmath-ast

Abstract Syntax Tree Expression Representation and Operations (kmath-ast)

This subproject implements the following features:

• Expression Language and its parser.
• MST (Mathematical Syntax Tree) as expression language's syntax intermediate representation.
• Type-safe builder for MST.
• Evaluating expressions by traversing MST.

Artifact:

This module is distributed in the artifact kscience.kmath:kmath-ast:0.1.4-dev-8.

Gradle:

repositories {
    maven { url 'https://dl.bintray.com/mipt-npm/kscience' }
    maven { url 'https://dl.bintray.com/mipt-npm/dev' }
    maven { url https://dl.bintray.com/hotkeytlt/maven' }
}

dependencies {
    implementation 'kscience.kmath:kmath-ast:0.1.4-dev-8'
}

Gradle Kotlin DSL:

repositories {
    maven("https://dl.bintray.com/mipt-npm/kscience")
    maven("https://dl.bintray.com/mipt-npm/dev")
    maven("https://dl.bintray.com/hotkeytlt/maven")
}

dependencies {
    implementation("kscience.kmath:kmath-ast:0.1.4-dev-8")
}

Dynamic expression code generation

On JVM

kmath-ast JVM module supports runtime code generation to eliminate overhead of tree traversal. Code generator builds a special implementation of Expression<T> with implemented invoke function.

For example, the following builder:

RealField.mstInField { symbol("x") + 2 }.compile()

… leads to generation of bytecode, which can be decompiled to the following Java class:

package kscience.kmath.asm.generated;

import java.util.Map;
import kotlin.jvm.functions.Function2;
import kscience.kmath.asm.internal.MapIntrinsics;
import kscience.kmath.expressions.Expression;
import kscience.kmath.expressions.Symbol;

public final class AsmCompiledExpression_45045_0 implements Expression<Double> {
    private final Object[] constants;

    public final Double invoke(Map<Symbol, Double> arguments) {
        return (Double)((Function2)this.constants[0]).invoke((Double)MapIntrinsics.getOrFail(arguments, "x"), 2);
    }

    public AsmCompiledExpression_45045_0(Object[] constants) {
        this.constants = constants;
    }
}

Example Usage

This API extends MST and MstExpression, so you may optimize as both of them:

RealField.mstInField { symbol("x") + 2 }.compile()
RealField.expression("x+2".parseMath())

Known issues

• The same classes may be generated and loaded twice, so it is recommended to cache compiled expressions to avoid class loading overhead.
• This API is not supported by non-dynamic JVM implementations (like TeaVM and GraalVM) because of using class loaders.

Contributed by Iaroslav Postovalov.

On JS

A similar feature is also available on JS.

RealField.mstInField { symbol("x") + 2 }.compile()

The code above returns expression implemented with such a JS function:

var executable = function (constants, arguments) {
  return constants[1](constants[0](arguments, "x"), 2);
};

Known issues

• This feature uses eval which can be unavailable in several environments.