diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/FunctionScope.java b/src/java/me/topchetoeu/jscript/compilation/scope/FunctionScope.java
new file mode 100644
index 0000000..3318f17
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/FunctionScope.java
@@ -0,0 +1,63 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+import java.util.HashMap;
+
+import me.topchetoeu.jscript.common.parsing.Location;
+
+public class FunctionScope extends Scope {
+    private final VariableList captures = new VariableList();
+    private final VariableList locals = new VariableList(captures);
+    private HashMap<VariableDescriptor, VariableDescriptor> childToParent = new HashMap<>();
+
+    private void removeCapture(String name) {
+        var res = captures.remove(name);
+        if (res != null) childToParent.remove(res);
+    }
+
+    @Override public VariableDescriptor define(String name, boolean readonly, Location loc) {
+        var old = locals.get(name);
+        if (old != null) return old;
+
+        removeCapture(name);
+        return locals.add(name, readonly);
+    }
+    @Override public VariableDescriptor defineStrict(String name, boolean readonly, Location loc) {
+        if (locals.has(name)) throw alreadyDefinedErr(loc, name);
+        else if (parent == null) throw new RuntimeException("Strict variables may be defined only in local scopes");
+        else return parent.defineStrict(name, readonly, loc);
+    }
+
+    @Override public VariableDescriptor get(String name, boolean capture) {
+        if (locals.has(name)) return locals.get(name);
+        if (captures.has(name)) return captures.get(name);
+
+        var parentVar = parent.get(name, true);
+        var childVar = captures.add(parentVar);
+
+        childToParent.put(childVar, parentVar);
+
+        return childVar;
+    }
+
+    public int localsCount() {
+        return locals.size();
+    }
+    public int offset() {
+        return captures.size() + locals.size();
+    }
+
+    public int[] getCaptureIndices() {
+        var res = new int[captures.size()];
+        var i = 0;
+
+        for (var el : captures) {
+            assert childToParent.containsKey(el);
+            res[i] = childToParent.get(el).index();
+        }
+
+        return res;
+    }
+
+    public FunctionScope() { super(); }
+    public FunctionScope(Scope parent) { super(parent); }
+}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/GlobalScope.java b/src/java/me/topchetoeu/jscript/compilation/scope/GlobalScope.java
new file mode 100644
index 0000000..75ba7d0
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/GlobalScope.java
@@ -0,0 +1,18 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+import me.topchetoeu.jscript.common.parsing.Location;
+
+public final class GlobalScope extends Scope {
+    @Override public VariableDescriptor define(String name, boolean readonly, Location loc) {
+        return null;
+    }
+    @Override public VariableDescriptor defineStrict(String name, boolean readonly, Location loc) {
+        return null;
+    }
+    @Override public VariableDescriptor get(String name, boolean capture) {
+        return null;
+    }
+    @Override public int offset() {
+        return 0;
+    }
+}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/LocalScope.java b/src/java/me/topchetoeu/jscript/compilation/scope/LocalScope.java
new file mode 100644
index 0000000..0ee6630
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/LocalScope.java
@@ -0,0 +1,46 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+import me.topchetoeu.jscript.common.parsing.Location;
+
+public class LocalScope extends Scope {
+    private final VariableList locals = new VariableList();
+
+    @Override public int offset() {
+        if (parent != null) return parent.offset() + locals.size();
+        else return locals.size();
+    }
+
+    @Override public VariableDescriptor define(String name, boolean readonly, Location loc) {
+        if (locals.has(name)) throw alreadyDefinedErr(loc, name);
+
+        return parent.define(name, readonly, loc);
+    }
+    @Override public VariableDescriptor defineStrict(String name, boolean readonly, Location loc) {
+        if (locals.has(name)) throw alreadyDefinedErr(loc, name);
+        return locals.add(name, readonly);
+    }
+
+    @Override public VariableDescriptor get(String name, boolean capture) {
+        var res = locals.get(name);
+
+        if (res != null) return res;
+        if (parent != null) return parent.get(name, capture);
+
+        return null;
+    }
+
+    @Override public boolean end() {
+        if (!super.end()) return false;
+
+        this.locals.freeze();
+        return true;
+    }
+
+    public Iterable<VariableDescriptor> all() {
+        return () -> locals.iterator();
+    }
+
+    public LocalScope(Scope parent) {
+        super(parent);
+    }
+}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/LocalScopeRecord.java b/src/java/me/topchetoeu/jscript/compilation/scope/LocalScopeRecord.java
deleted file mode 100644
index 070168d..0000000
--- a/src/java/me/topchetoeu/jscript/compilation/scope/LocalScopeRecord.java
+++ /dev/null
@@ -1,77 +0,0 @@
-package me.topchetoeu.jscript.compilation.scope;
-
-import java.util.ArrayList;
-
-public class LocalScopeRecord implements ScopeRecord {
-    public final LocalScopeRecord parent;
-
-    private final ArrayList<String> captures = new ArrayList<>();
-    private final ArrayList<String> locals = new ArrayList<>();
-
-    public String[] captures() {
-        return captures.toArray(String[]::new);
-    }
-    public String[] locals() {
-        return locals.toArray(String[]::new);
-    }
-
-    public LocalScopeRecord child() {
-        return new LocalScopeRecord(this);
-    }
-
-    public int localsCount() {
-        return locals.size();
-    }
-    public int capturesCount() {
-        return captures.size();
-    }
-
-    public int[] getCaptures() {
-        var buff = new int[captures.size()];
-        var i = 0;
-
-        for (var name : captures) {
-            var index = parent.getKey(name);
-            if (index instanceof Integer) buff[i++] = (int)index;
-        }
-
-        var res = new int[i];
-        System.arraycopy(buff, 0, res, 0, i);
-
-        return res;
-    }
-
-    public Object getKey(String name) {
-        var capI = captures.indexOf(name);
-        var locI = locals.lastIndexOf(name);
-        if (locI >= 0) return locI;
-        if (capI >= 0) return ~capI;
-        if (parent != null) {
-            var res = parent.getKey(name);
-            if (res != null && res instanceof Integer) {
-                captures.add(name);
-                return -captures.size();
-            }
-        }
-
-        return name;
-    }
-    public Object define(String name, boolean force) {
-        if (!force && locals.contains(name)) return locals.indexOf(name);
-        locals.add(name);
-        return locals.size() - 1;
-    }
-    public Object define(String name) {
-        return define(name, false);
-    }
-    public void undefine() {
-        locals.remove(locals.size() - 1);
-    }
-
-    public LocalScopeRecord() {
-        this.parent = null;
-    }
-    public LocalScopeRecord(LocalScopeRecord parent) {
-        this.parent = parent;
-    }
-}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/Scope.java b/src/java/me/topchetoeu/jscript/compilation/scope/Scope.java
new file mode 100644
index 0000000..6631abd
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/Scope.java
@@ -0,0 +1,68 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+import me.topchetoeu.jscript.common.parsing.Location;
+import me.topchetoeu.jscript.runtime.exceptions.SyntaxException;
+
+public abstract class Scope {
+    public final Scope parent;
+    private boolean active = true;
+    private Scope child;
+
+    protected final SyntaxException alreadyDefinedErr(Location loc, String name) {
+        return new SyntaxException(loc, String.format("Identifier '%s' has already been declared", name));
+    }
+
+    /**
+     * Defines an ES5-style variable
+     * @returns The index supplier of the variable if it is a local, or null if it is a global
+     * @throws SyntaxException If an ES2015-style variable with the same name exists anywhere from the current function to the current scope
+     * @throws RuntimeException If the scope is finalized or has an active child
+     */
+    public abstract VariableDescriptor define(String name, boolean readonly, Location loc);
+    /**
+     * Defines an ES2015-style variable
+     * @param readonly True if const, false if let
+     * @return The index supplier of the variable
+     * @throws SyntaxException If any variable with the same name exists in the current scope
+     * @throws RuntimeException If the scope is finalized or has an active child
+     */
+    public abstract VariableDescriptor defineStrict(String name, boolean readonly, Location loc);
+    /**
+     * Gets the index supplier of the given variable name, or null if it is a global
+     * 
+     * @param capture Used to signal to the scope that the variable is going to be captured.
+     * Not passing this could lead to a local variable being optimized out as an ES5-style variable,
+     * which could break the semantics of a capture
+     */
+    public abstract VariableDescriptor get(String name, boolean capture);
+    /**
+     * Gets the index offset from this scope to its children
+     */
+    public abstract int offset();
+
+    public boolean end() { 
+        if (!active) return false;
+
+        this.active = false;
+        if (this.parent != null) {
+            assert this.parent.child == this;
+            this.parent.child = this;
+        }
+
+        return true;
+    }
+
+    public final boolean active() { return active; }
+    public final Scope child() { return child; }
+
+    public Scope() {
+        this.parent = null;
+    }
+    public Scope(Scope parent) {
+        if (!parent.active) throw new RuntimeException("Parent is not active");
+        if (parent.child != null) throw new RuntimeException("Parent has an active child");
+
+        this.parent = parent;
+        this.parent.child = this;
+    }
+}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/ScopeRecord.java b/src/java/me/topchetoeu/jscript/compilation/scope/ScopeRecord.java
deleted file mode 100644
index fe08968..0000000
--- a/src/java/me/topchetoeu/jscript/compilation/scope/ScopeRecord.java
+++ /dev/null
@@ -1,7 +0,0 @@
-package me.topchetoeu.jscript.compilation.scope;
-
-public interface ScopeRecord {
-    public Object getKey(String name);
-    public Object define(String name);
-    public LocalScopeRecord child();
-}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/VariableDescriptor.java b/src/java/me/topchetoeu/jscript/compilation/scope/VariableDescriptor.java
new file mode 100644
index 0000000..29b3bb5
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/VariableDescriptor.java
@@ -0,0 +1,19 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+public abstract class VariableDescriptor {
+    public final boolean readonly;
+    public final String name;
+
+    public abstract int index();
+
+    public VariableDescriptor(String name, boolean readonly) {
+        this.name = name;
+        this.readonly = readonly;
+    }
+
+    public static VariableDescriptor of(String name, boolean readonly, int i) {
+        return new VariableDescriptor(name, readonly) {
+            @Override public int index() { return i; }
+        };
+    }
+}
diff --git a/src/java/me/topchetoeu/jscript/compilation/scope/VariableList.java b/src/java/me/topchetoeu/jscript/compilation/scope/VariableList.java
new file mode 100644
index 0000000..2fca3a8
--- /dev/null
+++ b/src/java/me/topchetoeu/jscript/compilation/scope/VariableList.java
@@ -0,0 +1,176 @@
+package me.topchetoeu.jscript.compilation.scope;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.function.IntSupplier;
+
+public class VariableList implements Iterable<VariableDescriptor> {
+    private class ListVar extends VariableDescriptor {
+        private ListVar next;
+        private ListVar prev;
+
+        @Override public int index() {
+            throw new RuntimeException("The index of a variable may not be retrieved until the scope has been finalized");
+            // var res = 0;
+            // if (offset != null) res = offset.getAsInt();
+
+            // for (var it = prev; it != null; it = it.prev) {
+            //     res++;
+            // }
+
+            // return res;
+        }
+
+        public ListVar(String name, boolean readonly, ListVar next, ListVar prev) {
+            super(name, readonly);
+
+            this.next = next;
+            this.prev = prev;
+        }
+    }
+
+    private ListVar first, last;
+
+    private HashMap<String, ListVar> map = new HashMap<>();
+
+    private HashMap<String, VariableDescriptor> frozenMap = null;
+    private ArrayList<VariableDescriptor> frozenList = null;
+
+    private final IntSupplier offset;
+
+    public boolean frozen() {
+        if (frozenMap != null) {
+            assert frozenList != null;
+            assert frozenMap != null;
+            assert map == null;
+            assert first == null;
+            assert last == null;
+
+            return true;
+        }
+        else {
+            assert frozenList == null;
+            assert frozenMap == null;
+            assert map != null;
+
+            return false;
+        }
+    }
+
+    public VariableDescriptor add(VariableDescriptor val) {
+        return add(val.name, val.readonly);
+    }
+    public VariableDescriptor add(String name, boolean readonly) {
+        if (frozen()) throw new RuntimeException("The scope has been frozen");
+        if (map.containsKey(name)) return map.get(name);
+
+        var res = new ListVar(name, readonly, null, last);
+        last.next = res;
+        last = res;
+        map.put(name, res);
+
+        return res;
+    }
+    public VariableDescriptor remove(String name) {
+        if (frozen()) throw new RuntimeException("The scope has been frozen");
+
+        var el = map.get(name);
+        if (el == null) return null;
+
+        el.prev.next = el.next;
+        el.next.prev = el.prev;
+
+        el.next = null;
+        el.prev = null;
+
+        return el;
+    }
+
+    public VariableDescriptor get(String name) {
+        return map.get(name);
+    }
+    public VariableDescriptor get(int i) {
+        if (frozen()) {
+            if (i < 0 || i >= frozenList.size()) return null;
+            return frozenList.get(i);
+        }
+        else {
+            if (i < 0 || i >= map.size()) return null;
+
+            if (i < map.size() / 2) {
+                var it = first;
+                for (var j = 0; j < i; it = it.next, j++);
+                return it;
+            }
+            else {
+                var it = last;
+                for (var j = map.size() - 1; j >= i; it = it.prev, j--);
+                return it;
+            }
+        }
+    }
+
+    public boolean has(String name) {
+        return this.get(name) != null;
+    }
+
+    public int size() {
+        if (frozen()) return frozenList.size();
+        else return map.size();
+    }
+
+    public void freeze() {
+        if (frozen()) return;
+
+        frozenMap = new HashMap<>();
+        frozenList = new ArrayList<>();
+
+        var i = 0;
+        if (offset != null) i = offset.getAsInt();
+
+        for (var it = first; it != null; it = it.next) {
+            frozenMap.put(it.name, VariableDescriptor.of(it.name, it.readonly, i++));
+        }
+    }
+
+    @Override public Iterator<VariableDescriptor> iterator() {
+        if (frozen()) return frozenList.iterator();
+        else return new Iterator<VariableDescriptor>() {
+            private ListVar curr = first;
+
+            @Override public boolean hasNext() {
+                return curr != null;
+            }
+            @Override public VariableDescriptor next() {
+                if (curr == null) return null;
+
+                var res = curr;
+                curr = curr.next;
+                return res;
+            }
+        };
+    }
+
+    public VariableDescriptor[] toArray() {
+        var res = new VariableDescriptor[size()];
+        var i = 0;
+
+        for (var el : this) res[i++] = el;
+
+        return res;
+    }
+
+    public VariableList(IntSupplier offset) {
+        this.offset = offset;
+    }
+    public VariableList(int offset) {
+        this.offset = () -> offset;
+    }
+    public VariableList(VariableList prev) {
+        this.offset = prev::size;
+    }
+    public VariableList() {
+        this.offset = null;
+    }
+}