115 lines
3.1 KiB
Markdown
115 lines
3.1 KiB
Markdown
# Abstract Syntax Tree Expression Representation and Operations (`kmath-ast`)
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This subproject implements the following features:
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- Expression Language and its parser.
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- MST (Mathematical Syntax Tree) as expression language's syntax intermediate representation.
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- Type-safe builder for MST.
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- Evaluating expressions by traversing MST.
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> #### Artifact:
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> This module is distributed in the artifact `kscience.kmath:kmath-ast:0.1.4-dev-8`.
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>
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> **Gradle:**
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>
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> ```gradle
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> repositories {
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> maven { url 'https://dl.bintray.com/mipt-npm/kscience' }
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> maven { url 'https://dl.bintray.com/mipt-npm/dev' }
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> maven { url https://dl.bintray.com/hotkeytlt/maven' }
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> }
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>
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> dependencies {
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> implementation 'kscience.kmath:kmath-ast:0.1.4-dev-8'
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> }
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> ```
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> **Gradle Kotlin DSL:**
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>
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> ```kotlin
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> repositories {
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> maven("https://dl.bintray.com/mipt-npm/kscience")
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> maven("https://dl.bintray.com/mipt-npm/dev")
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> maven("https://dl.bintray.com/hotkeytlt/maven")
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> }
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>
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> dependencies {
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> implementation("kscience.kmath:kmath-ast:0.1.4-dev-8")
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> }
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> ```
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>
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## Dynamic expression code generation
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### On JVM
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`kmath-ast` JVM module supports runtime code generation to eliminate overhead of tree traversal. Code generator builds
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a special implementation of `Expression<T>` with implemented `invoke` function.
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For example, the following builder:
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```kotlin
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RealField.mstInField { symbol("x") + 2 }.compile()
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```
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… leads to generation of bytecode, which can be decompiled to the following Java class:
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```java
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package kscience.kmath.asm.generated;
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import java.util.Map;
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import kotlin.jvm.functions.Function2;
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import kscience.kmath.asm.internal.MapIntrinsics;
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import kscience.kmath.expressions.Expression;
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import kscience.kmath.expressions.Symbol;
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public final class AsmCompiledExpression_45045_0 implements Expression<Double> {
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private final Object[] constants;
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public final Double invoke(Map<Symbol, Double> arguments) {
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return (Double)((Function2)this.constants[0]).invoke((Double)MapIntrinsics.getOrFail(arguments, "x"), 2);
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}
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public AsmCompiledExpression_45045_0(Object[] constants) {
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this.constants = constants;
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}
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}
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```
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### Example Usage
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This API extends MST and MstExpression, so you may optimize as both of them:
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```kotlin
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RealField.mstInField { symbol("x") + 2 }.compile()
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RealField.expression("x+2".parseMath())
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```
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#### Known issues
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- The same classes may be generated and loaded twice, so it is recommended to cache compiled expressions to avoid
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class loading overhead.
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- This API is not supported by non-dynamic JVM implementations (like TeaVM and GraalVM) because of using class loaders.
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Contributed by [Iaroslav Postovalov](https://github.com/CommanderTvis).
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### On JS
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A similar feature is also available on JS.
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```kotlin
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RealField.mstInField { symbol("x") + 2 }.compile()
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```
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The code above returns expression implemented with such a JS function:
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```js
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var executable = function (constants, arguments) {
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return constants[1](constants[0](arguments, "x"), 2);
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};
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```
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#### Known issues
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- This feature uses `eval` which can be unavailable in several environments.
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