Adds macro evaluator implementation (#924)

src/main/java/com/amazon/ion/impl/macro/Environment.kt

@@ -0,0 +1,30 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+package com.amazon.ion.impl.macro
+
+/**
+ * An `Environment` contains variable bindings for a given macro evaluation.
+ *
+ * The [arguments] is a list of expressions for the arguments that were passed to the current macro.
+ * It may also contain other expressions if the current macro invocation is part of a larger evaluation.
+ *
+ * The [argumentIndices] is a mapping from parameter index to the start of the corresponding expression in [arguments].
+ *
+ * The [parentEnvironment] is an environment to use if any of the expressions in this environment
+ * contains a variable that references something from an outer macro invocation.
+ */
+data class Environment private constructor(
+    // Any variables found here have to be looked up in [parentEnvironment]
+    val arguments: List<Expression>,
+    // TODO: Replace with IntArray
+    val argumentIndices: List<Int>,
+    val parentEnvironment: Environment?,
+) {
+    fun createChild(arguments: List<Expression>, argumentIndices: List<Int>) = Environment(arguments, argumentIndices, this)
+    companion object {
+        @JvmStatic
+        val EMPTY = Environment(emptyList(), emptyList(), null)
+        @JvmStatic
+        fun create(arguments: List<Expression>, argumentIndices: List<Int>) = Environment(arguments, argumentIndices, null)
+    }
+}

src/main/java/com/amazon/ion/impl/macro/Macro.kt

@@ -3,6 +3,7 @@
 package com.amazon.ion.impl.macro
 
 import com.amazon.ion.impl.*
+import com.amazon.ion.impl.macro.Macro.Parameter.Companion.zeroToManyTagged
 
 /**
  * A [Macro] is either a [SystemMacro] or a [TemplateMacro].
@@ -12,6 +13,11 @@ sealed interface Macro {
 
     data class Parameter(val variableName: String, val type: ParameterEncoding, val cardinality: ParameterCardinality) {
         override fun toString() = "$type::$variableName${cardinality.sigil}"
+
+        companion object {
+            @JvmStatic
+            fun zeroToManyTagged(name: String) = Parameter(name, Macro.ParameterEncoding.Tagged, Macro.ParameterCardinality.ZeroOrMore)
+        }
     }
 
     // TODO: See if we can DRY up ParameterEncoding and PrimitiveType
@@ -101,8 +107,8 @@ data class TemplateMacro(override val signature: List<Macro.Parameter>, val body
  * Macros that are built in, rather than being defined by a template.
  */
 enum class SystemMacro(override val signature: List<Macro.Parameter>) : Macro {
-    Values(listOf(Macro.Parameter("values", Macro.ParameterEncoding.Tagged, Macro.ParameterCardinality.ZeroOrMore))),
-    MakeString(listOf(Macro.Parameter("text", Macro.ParameterEncoding.Tagged, Macro.ParameterCardinality.ZeroOrMore))),
+    Values(listOf(zeroToManyTagged("values"))),
+    MakeString(listOf(zeroToManyTagged("text"))),
     // TODO: Other system macros
     ;
 }