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:
- 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 `scientifik:kmath-ast:0.1.4-dev-8`.
>
> **Gradle:**
>
> ```gradle
> repositories {
> maven { url 'https://dl.bintray.com/mipt-npm/scientifik' }
> maven { url 'https://dl.bintray.com/mipt-npm/dev' }
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> maven { url https://dl.bintray.com/hotkeytlt/maven' }
> }
>
> dependencies {
> implementation 'scientifik:kmath-ast:0.1.4-dev-8'
> }
> ```
> **Gradle Kotlin DSL:**
>
> ```kotlin
> repositories {
> maven("https://dl.bintray.com/mipt-npm/scientifik")
> maven("https://dl.bintray.com/mipt-npm/dev")
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> maven("https://dl.bintray.com/hotkeytlt/maven")
> }
>
> dependencies {
> implementation("scientifik:kmath-ast:0.1.4-dev-8")
> }
> ```
>
## Dynamic Expression Code Generation with ObjectWeb ASM
`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:
```kotlin
RealField.mstInField { symbol("x") + 2 }.compile()
```
… leads to generation of bytecode, which can be decompiled to the following Java class:
```java
package scientifik.kmath.asm.generated;
import java.util.Map;
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import scientifik.kmath.asm.internal.MapIntrinsics;
import scientifik.kmath.expressions.Expression;
import scientifik.kmath.operations.RealField;
public final class AsmCompiledExpression_1073786867_0 implements Expression<Double> {
private final RealField algebra;
public final Double invoke(Map<String, ? extends Double> arguments) {
return (Double)this.algebra.add(((Double)MapIntrinsics.getOrFail(arguments, "x")).doubleValue(), 2.0D);
}
public AsmCompiledExpression_1073786867_0(RealField algebra) {
this.algebra = algebra;
}
}
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```
### Example Usage
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())
```
### 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](https://github.com/CommanderTvis).