kmath/kmath-ast/README.md

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# AST-based expression representation and operations (`kmath-ast`)
2020-06-15 11:02:13 +03:00
This subproject implements the following features:
- Expression Language and its parser.
- MST as expression language's syntax intermediate representation.
- Type-safe builder of MST.
- Evaluating expressions by traversing MST.
## Dynamic expression code generation with OW2 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;
import scientifik.kmath.asm.internal.AsmCompiledExpression;
import scientifik.kmath.operations.Algebra;
import scientifik.kmath.operations.RealField;
// The class's name is build with MST's hash-code and collision fixing number.
public final class AsmCompiledExpression_45045_0 extends AsmCompiledExpression<Double> {
// Plain constructor
public AsmCompiledExpression_45045_0(Algebra algebra, Object[] constants) {
super(algebra, constants);
}
// The actual dynamic code:
public final Double invoke(Map<String, ? extends Double> arguments) {
return (Double)((RealField)super.algebra).add((Double)arguments.get("x"), (Double)2.0D);
}
}
```
### Example Usage
This API is an extension to MST and MSTExpression APIs. You may optimize both MST and MSTExpression:
```kotlin
RealField.mstInField { symbol("x") + 2 }.compile()
RealField.expression("2+2".parseMath())
```
### Known issues
- Using numeric algebras causes boxing and calling bridge methods.
- 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).