Create function definition tools

src/main/kotlin/io/smnp/api/callable/Function.kt

@@ -0,0 +1,25 @@
+package io.smnp.api.callable
+
+import io.smnp.api.environment.Environment
+import io.smnp.api.model.Value
+
+abstract class Function(val name: String) {
+    private var definitions: List<FunctionDefinition> = mutableListOf()
+
+    abstract fun define(new: FunctionDefinitionTool)
+
+    init {
+        definitions = FunctionDefinitionTool().apply { define(this) }.definitions
+    }
+
+    fun call(environment: Environment, vararg arguments: Value): Value {
+        val (definition, args) = definitions
+            .map { Pair(it, it.signature.parse(arguments.toList())) }
+            .first { (_, args) -> args.signatureMatched }
+            // TODO: Throw exception if signature is not matched
+        return definition.body(environment, args.arguments)
+    }
+
+    val signature: String
+        get() = definitions.joinToString("\nor\n") { "$name${it.signature}" }
+}

src/main/kotlin/io/smnp/api/callable/FunctionDefinition.kt

@@ -0,0 +1,7 @@
+package io.smnp.api.callable
+
+import io.smnp.api.environment.Environment
+import io.smnp.api.model.Value
+import io.smnp.api.signature.Signature
+
+class FunctionDefinition(val signature: Signature, val body: (Environment, List<Value>) -> Value)

src/main/kotlin/io/smnp/api/callable/FunctionDefinitionTool.kt

@@ -0,0 +1,20 @@
+package io.smnp.api.callable
+
+import io.smnp.api.environment.Environment
+import io.smnp.api.model.Value
+import io.smnp.api.signature.Signature
+
+class FunctionDefinitionTool {
+    val definitions: MutableList<FunctionDefinition> = mutableListOf()
+
+    infix fun function(signature: Signature): FunctionDefinitionToolStage2 {
+        return FunctionDefinitionToolStage2(signature)
+    }
+
+    inner class FunctionDefinitionToolStage2(private val signature: Signature) {
+        infix fun define(body: (Environment, List<Value>) -> Value) {
+            definitions.add(FunctionDefinition(signature, body))
+        }
+    }
+
+}

src/main/kotlin/io/smnp/api/model/ArgumentsList.kt

@@ -1,11 +1,11 @@
 package io.smnp.api.model
 
-class ArgumentsList(val isValid: Boolean, val arguments: List<Value>) {
+class ArgumentsList(val signatureMatched: Boolean, val arguments: List<Value>) {
     operator fun get(index: Int) = arguments[index]
 
     fun toArray() = arguments.toTypedArray()
 
-    override fun toString() = if(isValid) "valid($arguments)" else "invalid"
+    override fun toString() = if(signatureMatched) "valid($arguments)" else "invalid"
 
     companion object {
         fun valid(arguments: List<Value>): ArgumentsList {