forked from kscience/kmath
62 lines
2.1 KiB
Markdown
62 lines
2.1 KiB
Markdown
# AST-based 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 as expression language's syntax intermediate representation.
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- Type-safe builder of MST.
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- Evaluating expressions by traversing MST.
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## Dynamic expression code generation with OW2 ASM
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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 scientifik.kmath.asm.generated;
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import java.util.Map;
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import scientifik.kmath.asm.internal.AsmCompiledExpression;
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import scientifik.kmath.operations.Algebra;
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import scientifik.kmath.operations.RealField;
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// The class's name is build with MST's hash-code and collision fixing number.
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public final class AsmCompiledExpression_45045_0 extends AsmCompiledExpression<Double> {
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// Plain constructor
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public AsmCompiledExpression_45045_0(Algebra algebra, Object[] constants) {
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super(algebra, constants);
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}
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// The actual dynamic code:
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public final Double invoke(Map<String, ? extends Double> arguments) {
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return (Double)((RealField)super.algebra).add((Double)arguments.get("x"), (Double)2.0D);
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}
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}
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```
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### Example Usage
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This API is an extension to MST and MSTExpression APIs. You may optimize both MST and MSTExpression:
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```kotlin
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RealField.mstInField { symbol("x") + 2 }.compile()
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RealField.expression("2+2".parseMath())
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```
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### Known issues
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- Using numeric algebras causes boxing and calling bridge methods.
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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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