Add C API functions for working with lists:

- wrenEnsureSlots()
  Lets you go the foreign slot stack to make room for a temporary work
  area.

- wrenSetSlotNewList()
  Creates a new empty list and stores it in a slot.

- wrenInsertInList()
  Takes a value from one slot and inserts it into the list in another.

Still need more functions like getting elements from a list, removing,
etc. but this at least lets you create, populate, and return lists from
foreign methods.

test/api/lists.c

@@ -0,0 +1,46 @@
+#include <string.h>
+
+#include "lists.h"
+
+static void newList(WrenVM* vm)
+{
+  wrenSetSlotNewList(vm, 0);
+}
+
+// Helper function to store a double in a slot then insert it into the list at
+// slot zero.
+static void insertNumber(WrenVM* vm, int index, double value)
+{
+  wrenSetSlotDouble(vm, 1, value);
+  wrenInsertInList(vm, 0, index, 1);
+}
+
+static void insert(WrenVM* vm)
+{
+  wrenSetSlotNewList(vm, 0);
+  
+  wrenEnsureSlots(vm, 2);
+  
+  // Appending.
+  insertNumber(vm, 0, 1.0);
+  insertNumber(vm, 1, 2.0);
+  insertNumber(vm, 2, 3.0);
+  
+  // Inserting.
+  insertNumber(vm, 0, 4.0);
+  insertNumber(vm, 1, 5.0);
+  insertNumber(vm, 2, 6.0);
+  
+  // Negative indexes.
+  insertNumber(vm, -1, 7.0);
+  insertNumber(vm, -2, 8.0);
+  insertNumber(vm, -3, 9.0);
+}
+
+WrenForeignMethodFn listsBindMethod(const char* signature)
+{
+  if (strcmp(signature, "static Lists.newList()") == 0) return newList;
+  if (strcmp(signature, "static Lists.insert()") == 0) return insert;
+
+  return NULL;
+}

test/api/lists.h

@@ -0,0 +1,3 @@
+#include "wren.h"
+
+WrenForeignMethodFn listsBindMethod(const char* signature);

test/api/lists.wren

@@ -0,0 +1,10 @@
+class Lists {
+  foreign static newList()
+  foreign static insert()
+}
+
+var list = Lists.newList()
+System.print(list is List) // expect: true
+System.print(list.count) // expect: 0
+
+System.print(Lists.insert()) // expect: [4, 5, 6, 1, 2, 3, 9, 8, 7]

test/api/main.c

@@ -7,6 +7,7 @@
 #include "benchmark.h"
 #include "call.h"
 #include "foreign_class.h"
+#include "lists.h"
 #include "slots.h"
 #include "value.h"
 
@@ -36,6 +37,9 @@ static WrenForeignMethodFn bindForeignMethod(
   method = foreignClassBindMethod(fullName);
   if (method != NULL) return method;
   
+  method = listsBindMethod(fullName);
+  if (method != NULL) return method;
+  
   method = slotsBindMethod(fullName);
   if (method != NULL) return method;
   

test/api/slots.c

@@ -1,3 +1,4 @@
+#include <stdio.h>
 #include <string.h>
 
 #include "slots.h"
@@ -73,11 +74,38 @@ static void setSlots(WrenVM* vm)
   }
 }
 
+static void ensure(WrenVM* vm)
+{
+  int before = wrenGetSlotCount(vm);
+  
+  wrenEnsureSlots(vm, 20);
+  
+  int after = wrenGetSlotCount(vm);
+  
+  // Use the slots to make sure they're available.
+  for (int i = 0; i < 20; i++)
+  {
+    wrenSetSlotDouble(vm, i, i);
+  }
+  
+  int sum = 0;
+
+  for (int i = 0; i < 20; i++)
+  {
+    sum += (int)wrenGetSlotDouble(vm, i);
+  }
+  
+  char result[100];
+  sprintf(result, "%d -> %d (%d)", before, after, sum);
+  wrenSetSlotString(vm, 0, result);
+}
+
 WrenForeignMethodFn slotsBindMethod(const char* signature)
 {
   if (strcmp(signature, "static Slots.noSet") == 0) return noSet;
   if (strcmp(signature, "static Slots.getSlots(_,_,_,_,_)") == 0) return getSlots;
   if (strcmp(signature, "static Slots.setSlots(_,_,_,_)") == 0) return setSlots;
+  if (strcmp(signature, "static Slots.ensure()") == 0) return ensure;
 
   return NULL;
 }

test/api/slots.wren

@@ -1,9 +1,8 @@
 class Slots {
   foreign static noSet
-
   foreign static getSlots(bool, num, string, bytes, value)
-
   foreign static setSlots(a, b, c, d)
+  foreign static ensure()
 }
 
 // If nothing is set in the return slot, it retains its previous value, the
@@ -14,3 +13,5 @@ var value = ["value"]
 System.print(Slots.getSlots(true, "by\0te", 12.34, "str", value) == value) // expect: true
 
 System.print(Slots.setSlots(value, 0, 0, 0) == value) // expect: true
+
+System.print(Slots.ensure()) // expect: 1 -> 20 (190)