kmath/kmath-ast/README.md

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# 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](src/jvmMain/kotlin/kscience/kmath/ast/parser.kt) : Expression language and its parser
- [mst](src/commonMain/kotlin/kscience/kmath/ast/MST.kt) : MST (Mathematical Syntax Tree) as expression language's syntax intermediate representation
- [mst-building](src/commonMain/kotlin/kscience/kmath/ast/MstAlgebra.kt) : MST building algebraic structure
- [mst-interpreter](src/commonMain/kotlin/kscience/kmath/ast/MST.kt) : MST interpreter
- [mst-jvm-codegen](src/jvmMain/kotlin/kscience/kmath/asm/asm.kt) : Dynamic MST to JVM bytecode compiler
- [mst-js-codegen](src/jsMain/kotlin/kscience/kmath/estree/estree.kt) : Dynamic MST to JS compiler
> #### Artifact:
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>
> This module artifact: `kscience.kmath:kmath-ast:0.2.0-dev-4`.
>
> Bintray release version: [ ![Download](https://api.bintray.com/packages/mipt-npm/kscience/kmath-ast/images/download.svg) ](https://bintray.com/mipt-npm/kscience/kmath-ast/_latestVersion)
>
> Bintray development version: [ ![Download](https://api.bintray.com/packages/mipt-npm/dev/kmath-ast/images/download.svg) ](https://bintray.com/mipt-npm/dev/kmath-ast/_latestVersion)
>
> **Gradle:**
>
> ```gradle
> repositories {
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> maven { url "https://dl.bintray.com/kotlin/kotlin-eap" }
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> maven { url 'https://dl.bintray.com/mipt-npm/kscience' }
> maven { url 'https://dl.bintray.com/mipt-npm/dev' }
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> maven { url 'https://dl.bintray.com/hotkeytlt/maven' }
> }
>
> dependencies {
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> implementation 'kscience.kmath:kmath-ast:0.2.0-dev-4'
> }
> ```
> **Gradle Kotlin DSL:**
>
> ```kotlin
> repositories {
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> maven("https://dl.bintray.com/kotlin/kotlin-eap")
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> maven("https://dl.bintray.com/mipt-npm/kscience")
> maven("https://dl.bintray.com/mipt-npm/dev")
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> maven("https://dl.bintray.com/hotkeytlt/maven")
> }
>
> dependencies {
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> implementation("kscience.kmath:kmath-ast:0.2.0-dev-4")
> }
> ```
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## Dynamic expression code generation
### On JVM
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`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.
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For example, the following builder:
```kotlin
RealField.mstInField { symbol("x") + 2 }.compile()
```
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… leads to generation of bytecode, which can be decompiled to the following Java class:
```java
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package kscience.kmath.asm.generated;
import java.util.Map;
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import kotlin.jvm.functions.Function2;
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import kscience.kmath.asm.internal.MapIntrinsics;
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> {
private final Object[] constants;
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public final Double invoke(Map<Symbol, Double> arguments) {
return (Double)((Function2)this.constants[0]).invoke((Double)MapIntrinsics.getOrFail(arguments, "x"), 2);
}
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public AsmCompiledExpression_45045_0(Object[] constants) {
this.constants = constants;
}
}
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```
### Example Usage
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This API extends MST and MstExpression, so you may optimize as both of them:
```kotlin
RealField.mstInField { symbol("x") + 2 }.compile()
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RealField.expression("x+2".parseMath())
```
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#### Known issues
- 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.
- This API is not supported by non-dynamic JVM implementations (like TeaVM and GraalVM) because of using class loaders.
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### On JS
A similar feature is also available on JS.
```kotlin
RealField.mstInField { symbol("x") + 2 }.compile()
```
The code above returns expression implemented with such a JS function:
```js
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.