Refactored Expression tree API

kmath-commons/src/main/kotlin/scientifik/kmath/commons/expressions/DiffExpression.kt

@@ -2,9 +2,8 @@ package scientifik.kmath.commons.expressions
 
 import org.apache.commons.math3.analysis.differentiation.DerivativeStructure
 import scientifik.kmath.expressions.Expression
-import scientifik.kmath.expressions.ExpressionContext
+import scientifik.kmath.expressions.ExpressionField
 import scientifik.kmath.operations.ExtendedField
-import scientifik.kmath.operations.Field
 import kotlin.properties.ReadOnlyProperty
 import kotlin.reflect.KProperty
 
@@ -113,7 +112,7 @@ fun DiffExpression.derivative(name: String) = derivative(name to 1)
 /**
  * A context for [DiffExpression] (not to be confused with [DerivativeStructure])
  */
-object DiffExpressionContext : ExpressionContext<Double>, Field<DiffExpression> {
+object DiffExpressionContext : ExpressionField<Double, DiffExpression> {
     override fun variable(name: String, default: Double?) =
         DiffExpression { variable(name, default?.const()) }
 

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/Expression.kt

@@ -1,5 +1,8 @@
 package scientifik.kmath.expressions
 
+import scientifik.kmath.operations.Field
+import scientifik.kmath.operations.Space
+
 /**
  * An elementary function that could be invoked on a map of arguments
  */
@@ -12,16 +15,97 @@ operator fun <T> Expression<T>.invoke(vararg pairs: Pair<String, T>): T = invoke
 /**
  * A context for expression construction
  */
-interface ExpressionContext<T> {
+interface ExpressionContext<T, E : Expression<T>> {
     /**
      * Introduce a variable into expression context
      */
-    fun variable(name: String, default: T? = null): Expression<T>
+    fun variable(name: String, default: T? = null): E
 
     /**
      * A constant expression which does not depend on arguments
      */
-    fun const(value: T): Expression<T>
+    fun const(value: T): E
+
+    fun produce(node: SyntaxTreeNode): E
+}
+
+interface ExpressionSpace<T, E : Expression<T>> : Space<E>, ExpressionContext<T, E> {
+
+    open fun produceSingular(value: String): E = variable(value)
+
+    open fun produceUnary(operation: String, value: E): E {
+        return when (operation) {
+            UnaryNode.PLUS_OPERATION -> value
+            UnaryNode.MINUS_OPERATION -> -value
+            else -> error("Unary operation $operation is not supported by $this")
+        }
+    }
+
+    open fun produceBinary(operation: String, left: E, right: E): E {
+        return when (operation) {
+            BinaryNode.PLUS_OPERATION -> left + right
+            BinaryNode.MINUS_OPERATION -> left - right
+            else -> error("Binary operation $operation is not supported by $this")
+        }
+    }
+
+    override fun produce(node: SyntaxTreeNode): E {
+        return when (node) {
+            is NumberNode -> error("Single number nodes are not supported")
+            is SingularNode -> produceSingular(node.value)
+            is UnaryNode -> produceUnary(node.operation, produce(node.value))
+            is BinaryNode -> {
+                when (node.operation) {
+                    BinaryNode.TIMES_OPERATION -> {
+                        if (node.left is NumberNode) {
+                            return produce(node.right) * node.left.value
+                        } else if (node.right is NumberNode) {
+                            return produce(node.left) * node.right.value
+                        }
+                    }
+                    BinaryNode.DIV_OPERATION -> {
+                        if (node.right is NumberNode) {
+                            return produce(node.left) / node.right.value
+                        }
+                    }
+                }
+                produceBinary(node.operation, produce(node.left), produce(node.right))
+            }
+        }
+    }
+}
+
+interface ExpressionField<T, E : Expression<T>> : Field<E>, ExpressionSpace<T, E> {
+    fun const(value: Double): E = one.times(value)
+
+    override fun produce(node: SyntaxTreeNode): E {
+        if (node is BinaryNode) {
+            when (node.operation) {
+                BinaryNode.PLUS_OPERATION -> {
+                    if (node.left is NumberNode) {
+                        return produce(node.right) + one * node.left.value
+                    } else if (node.right is NumberNode) {
+                        return produce(node.left) + one * node.right.value
+                    }
+                }
+                BinaryNode.MINUS_OPERATION -> {
+                    if (node.left is NumberNode) {
+                        return one * node.left.value - produce(node.right)
+                    } else if (node.right is NumberNode) {
+                        return produce(node.left) - one * node.right.value
+                    }
+                }
+            }
+        }
+        return super.produce(node)
+    }
+
+    override fun produceBinary(operation: String, left: E, right: E): E {
+        return when (operation) {
+            BinaryNode.TIMES_OPERATION -> left * right
+            BinaryNode.DIV_OPERATION -> left / right
+            else -> super.produceBinary(operation, left, right)
+        }
+    }
 
-    fun produce(node: SyntaxTreeNode): Expression<T>
 }

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/SyntaxTreeNode.kt

@@ -4,20 +4,24 @@ sealed class SyntaxTreeNode
 
 data class SingularNode(val value: String) : SyntaxTreeNode()
 
-data class UnaryNode(val operation: String, val value: SyntaxTreeNode): SyntaxTreeNode(){
+data class NumberNode(val value: Number) : SyntaxTreeNode()
-    companion object{
+
+data class UnaryNode(val operation: String, val value: SyntaxTreeNode) : SyntaxTreeNode() {
+    companion object {
         const val PLUS_OPERATION = "+"
         const val MINUS_OPERATION = "-"
         const val NOT_OPERATION = "!"
         const val ABS_OPERATION = "abs"
         const val SIN_OPERATION = "sin"
-        const val cos_OPERATION = "cos"
+        const val COS_OPERATION = "cos"
+        const val EXP_OPERATION = "exp"
+        const val LN_OPERATION = "ln"
         //TODO add operations
     }
 }
 
-data class BinaryNode(val operation: String, val left: SyntaxTreeNode, val right: SyntaxTreeNode): SyntaxTreeNode(){
+data class BinaryNode(val operation: String, val left: SyntaxTreeNode, val right: SyntaxTreeNode) : SyntaxTreeNode() {
-    companion object{
+    companion object {
         const val PLUS_OPERATION = "+"
         const val MINUS_OPERATION = "-"
         const val TIMES_OPERATION = "*"

kmath-core/src/commonMain/kotlin/scientifik/kmath/expressions/functionalExpressions.kt

@@ -40,12 +40,10 @@ internal class DivExpession<T>(val context: Field<T>, val expr: Expression<T>, v
 open class FunctionalExpressionSpace<T>(
     val space: Space<T>,
     one: T
-) : Space<Expression<T>>, ExpressionContext<T> {
+) : Space<Expression<T>>, ExpressionSpace<T,Expression<T>> {
 
     override val zero: Expression<T> = ConstantExpression(space.zero)
 
-    val one: Expression<T> = ConstantExpression(one)
-
     override fun const(value: T): Expression<T> = ConstantExpression(value)
 
     override fun variable(name: String, default: T?): Expression<T> = VariableExpression(name, default)
@@ -60,46 +58,17 @@ open class FunctionalExpressionSpace<T>(
 
     operator fun T.plus(arg: Expression<T>) = arg + this
     operator fun T.minus(arg: Expression<T>) = arg - this
-
-    fun const(value: Double): Expression<T> = one.times(value)
-
-    open fun produceSingular(value: String): Expression<T> {
-        val numberValue = value.toDoubleOrNull()
-        return if (numberValue == null) {
-            variable(value)
-        } else {
-            const(numberValue)
-        }
-    }
-
-    open fun produceUnary(operation: String, value: Expression<T>): Expression<T> {
-        return when (operation) {
-            UnaryNode.PLUS_OPERATION -> value
-            UnaryNode.MINUS_OPERATION -> -value
-            else -> error("Unary operation $operation is not supported by $this")
-        }
-    }
-
-    open fun produceBinary(operation: String, left: Expression<T>, right: Expression<T>): Expression<T> {
-        return when (operation) {
-            BinaryNode.PLUS_OPERATION -> left + right
-            BinaryNode.MINUS_OPERATION -> left - right
-            else -> error("Binary operation $operation is not supported by $this")
-        }
-    }
-
-    override fun produce(node: SyntaxTreeNode): Expression<T> {
-        return when (node) {
-            is SingularNode -> produceSingular(node.value)
-            is UnaryNode -> produceUnary(node.operation, produce(node.value))
-            is BinaryNode -> produceBinary(node.operation, produce(node.left), produce(node.right))
-        }
-    }
 }
 
 open class FunctionalExpressionField<T>(
     val field: Field<T>
-) : Field<Expression<T>>, FunctionalExpressionSpace<T>(field, field.one) {
+) : ExpressionField<T,Expression<T>>, FunctionalExpressionSpace<T>(field, field.one) {
+
+    override val one: Expression<T>
+        get() = const(this.field.one)
+
+    override fun const(value: Double): Expression<T> = const(field.run { one*value})
+
     override fun multiply(a: Expression<T>, b: Expression<T>): Expression<T> = ProductExpression(field, a, b)
 
     override fun divide(a: Expression<T>, b: Expression<T>): Expression<T> = DivExpession(field, a, b)
@@ -109,17 +78,4 @@ open class FunctionalExpressionField<T>(
 
     operator fun T.times(arg: Expression<T>) = arg * this
     operator fun T.div(arg: Expression<T>) = arg / this
-
-    override fun produce(node: SyntaxTreeNode): Expression<T> {
-        //TODO bring together numeric and typed expressions
-        return super.produce(node)
-    }
-
-    override fun produceBinary(operation: String, left: Expression<T>, right: Expression<T>): Expression<T> {
-        return when (operation) {
-            BinaryNode.TIMES_OPERATION -> left * right
-            BinaryNode.DIV_OPERATION -> left / right
-            else -> super.produceBinary(operation, left, right)
-        }
-    }
 }