kmath/kmath-ast/docs/README-TEMPLATE.md
2021-03-16 21:17:26 +03:00

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# Abstract Syntax Tree Expression Representation and Operations (`kmath-ast`)
This subproject implements the following features:
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## 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:
```kotlin
DoubleField.mstInField { symbol("x") + 2 }.compile()
```
leads to generation of bytecode, which can be decompiled to the following Java class:
```java
package space.kscience.kmath.asm.generated;
import java.util.Map;
import kotlin.jvm.functions.Function2;
import space.kscience.kmath.asm.internal.MapIntrinsics;
import space.kscience.kmath.expressions.Expression;
import space.kscience.kmath.expressions.Symbol;
public final class AsmCompiledExpression_45045_0 implements Expression<Double> {
private final Object[] constants;
public final Double invoke(Map<Symbol, ? extends 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:
```kotlin
DoubleField.mstInField { symbol("x") + 2 }.compile()
DoubleField.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.
### On JS
A similar feature is also available on JS.
```kotlin
DoubleField.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.