# AST-based expression representation and operations (`kmath-ast`) 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` 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 { // Plain constructor public AsmCompiledExpression_45045_0(Algebra algebra, Object[] constants) { super(algebra, constants); } // The actual dynamic code: public final Double invoke(Map 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).