diff --git a/develop.lola b/develop.lola
index ef5060d..9206653 100644
--- a/develop.lola
+++ b/develop.lola
@@ -1,99 +1,3 @@
 
-// Without optimizations:
-//     Number of runs:     100
-//     Mean time:          74276.98325 µs
-//     Mean #instructions: 1122
-//     Mean #stalls:       0
-//     Mean instruction/s: 15105.621565480044
-
-// With string-copy-removal:
-//     Number of runs:     100
-//     Mean time:          19746.62485 µs
-//     Mean #instructions: 1122
-//     Mean #stalls:       0
-//     Mean instruction/s: 56819.83673275689
-
-// Make clone() return a refcounted string instead of a flat clone:
-//     Number of runs:     100
-//     Mean time:          17273.46292 µs
-//     Mean #instructions: 1122
-//     Mean #stalls:       0
-//     Mean instruction/s: 64955.128291090805
-
-function dump(str) { }
-
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-dump("hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello");
-
-var deep_copy = [
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ],
-  [ "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello", "hello" ]
-];
-
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
-dump(deep_copy, deep_copy, deep_copy, deep_copy, deep_copy, deep_copy);
\ No newline at end of file
+var x = "a";
+x[0] = true;
\ No newline at end of file
diff --git a/documentation/README.md b/documentation/README.md
index 760431f..a44b498 100644
--- a/documentation/README.md
+++ b/documentation/README.md
@@ -144,7 +144,7 @@ LoLa provides several operators that execute arithmetic, logic or comparison ope
 | `a <= b` | `number` |Less-or-equal test|`(3 <= 2) == false`|
 | `a > b` | `number` |Greater-than test|`(3 > 2) == true`|
 | `a < b` | `number` |Less-than test|`(3 < 2) == false`|
-| `a[i]` | `array` | Array index | `([1,2,3])[1] == 2` |
+| `a[i]` | `array`, `string` | Array index, string index | `([1,2,3])[1] == 2` |
 
 ### Operator Precedence 
 
diff --git a/src/frontend/main.zig b/src/frontend/main.zig
index f8afa7e..d216f8c 100644
--- a/src/frontend/main.zig
+++ b/src/frontend/main.zig
@@ -337,7 +337,16 @@ fn run(options: RunCLI, files: []const []const u8) !u8 {
         while (true) {
             var result = vm.execute(options.limit) catch |err| {
                 var stderr = std.io.getStdErr().writer();
-                try stderr.print("Panic during execution: {}\n", .{@errorName(err)});
+
+                if (std.builtin.mode == .Debug) {
+                    if (@errorReturnTrace()) |err_trace| {
+                        std.debug.dumpStackTrace(err_trace.*);
+                    } else {
+                        try stderr.print("Panic during execution: {}\n", .{@errorName(err)});
+                    }
+                } else {
+                    try stderr.print("Panic during execution: {}\n", .{@errorName(err)});
+                }
                 try stderr.print("Call stack:\n", .{});
 
                 try vm.printStackTrace(stderr);
diff --git a/src/library/compiler/analysis.zig b/src/library/compiler/analysis.zig
index e07013c..7227713 100644
--- a/src/library/compiler/analysis.zig
+++ b/src/library/compiler/analysis.zig
@@ -21,6 +21,8 @@ const AnalysisState = struct {
 
 const ValidationError = error{OutOfMemory};
 
+const array_or_string = TypeSet.init(.{ .array, .string });
+
 fn expressionTypeToString(src: ast.Expression.Type) []const u8 {
     return switch (src) {
         .array_indexer => "array indexer",
@@ -56,10 +58,20 @@ fn validateExpression(state: *AnalysisState, diagnostics: *Diagnostics, scope: *
             const array_type = try validateExpression(state, diagnostics, scope, indexer.value.*);
             const index_type = try validateExpression(state, diagnostics, scope, indexer.index.*);
 
-            try performTypeCheck(diagnostics, indexer.value.location, TypeSet.from(.array), array_type);
+            try performTypeCheck(diagnostics, indexer.value.location, array_or_string, array_type);
             try performTypeCheck(diagnostics, indexer.index.location, TypeSet.from(.number), index_type);
 
-            return TypeSet.any;
+            if (array_type.contains(.array)) {
+                // when we're possibly indexing an array,
+                // we return a value of type `any`
+                return TypeSet.any;
+            } else if (array_type.contains(.string)) {
+                // when we are not an array, but a string,
+                // we can only return a number.
+                return TypeSet.from(.number);
+            } else {
+                return TypeSet.empty;
+            }
         },
 
         .variable_expr => |variable_name| {
@@ -178,17 +190,24 @@ fn validateStore(state: *AnalysisState, diagnostics: *Diagnostics, scope: *Scope
         });
         return;
     }
+
     switch (expression.type) {
         .array_indexer => |indexer| {
             const array_val = try validateExpression(state, diagnostics, scope, indexer.value.*);
             const index_val = try validateExpression(state, diagnostics, scope, indexer.index.*);
 
-            try performTypeCheck(diagnostics, indexer.value.location, TypeSet.from(.array), array_val);
+            try performTypeCheck(diagnostics, indexer.value.location, array_or_string, array_val);
             try performTypeCheck(diagnostics, indexer.index.location, TypeSet.from(.number), index_val);
 
+            if (array_val.contains(.string) and !array_val.contains(.array)) {
+                // when we are sure we write into a string, but definitly not an array
+                // check if we're writing a number.
+                try performTypeCheck(diagnostics, expression.location, TypeSet.from(.number), type_hint);
+            }
+
             // now propagate the store validation back to the lvalue.
             // Note that we can assume that the lvalue _is_ a array, as it would be a type mismatch otherwise.
-            try validateStore(state, diagnostics, scope, indexer.value.*, TypeSet.from(.array));
+            try validateStore(state, diagnostics, scope, indexer.value.*, array_or_string.intersection(array_val));
         },
 
         .variable_expr => |variable_name| {
diff --git a/src/library/runtime/value.zig b/src/library/runtime/value.zig
index c1dcb09..bff9820 100644
--- a/src/library/runtime/value.zig
+++ b/src/library/runtime/value.zig
@@ -435,23 +435,13 @@ pub const String = struct {
     /// Clones `text` with the given parameter and stores the
     /// duplicated value.
     pub fn init(allocator: *std.mem.Allocator, text: []const u8) !Self {
-        const alignment = @alignOf(usize);
-
-        const ptr_offset = std.mem.alignForward(text.len, alignment);
-        const buffer = try allocator.allocAdvanced(
+        var string = try initUninitialized(allocator, text.len);
+        std.mem.copy(
             u8,
-            alignment,
-            ptr_offset + @sizeOf(usize),
-            .exact,
+            string.obtainMutableStorage() catch unreachable,
+            text,
         );
-        std.mem.copy(u8, buffer, text);
-        std.mem.writeIntNative(usize, buffer[ptr_offset..][0..@sizeOf(usize)], 1);
-
-        return Self{
-            .allocator = allocator,
-            .contents = buffer[0..text.len],
-            .refcount = @ptrCast(*usize, @alignCast(alignment, buffer.ptr + ptr_offset)),
-        };
+        return string;
     }
 
     /// Returns a string that will take ownership of the passed `text` and
diff --git a/src/library/runtime/vm.zig b/src/library/runtime/vm.zig
index 463fbad..6fee8c5 100644
--- a/src/library/runtime/vm.zig
+++ b/src/library/runtime/vm.zig
@@ -302,40 +302,81 @@ pub const VM = struct {
             },
 
             .array_load => {
-                var array_val = try self.pop();
-                defer array_val.deinit();
+                var indexed_val = try self.pop();
+                defer indexed_val.deinit();
 
                 var index_val = try self.pop();
                 defer index_val.deinit();
 
-                const item = try getArrayItem(&array_val, index_val);
+                const index = try index_val.toInteger(usize);
+
+                var dupe: Value = switch (indexed_val) {
+                    .array => |arr| blk: {
+                        if (index >= arr.contents.len)
+                            return error.IndexOutOfRange;
+
+                        break :blk try arr.contents[index].clone();
+                    },
+                    .string => |str| blk: {
+                        if (index >= str.contents.len)
+                            return error.IndexOutOfRange;
+
+                        break :blk Value.initInteger(u8, str.contents[index]);
+                    },
+                    else => return error.TypeMismatch,
+                };
 
-                var dupe = try item.clone();
                 errdefer dupe.deinit();
 
                 try self.push(dupe);
             },
 
             .array_store => {
-                var array_val = try self.pop();
-                errdefer array_val.deinit();
+                var indexed_val = try self.pop();
+                errdefer indexed_val.deinit();
 
                 var index_val = try self.pop();
                 defer index_val.deinit();
 
-                var value = try self.pop();
-                {
+                if (indexed_val == .array) {
+                    var value = try self.pop();
                     // only destroy value when we fail to get the array item,
                     // otherwise the value is stored in the array and must not
                     // be deinitialized after that
                     errdefer value.deinit();
 
-                    const item = try getArrayItem(&array_val, index_val);
+                    const index = try index_val.toInteger(usize);
+                    if (index >= indexed_val.array.contents.len)
+                        return error.IndexOutOfRange;
 
-                    item.replaceWith(value);
+                    indexed_val.array.contents[index].replaceWith(value);
+                } else if (indexed_val == .string) {
+                    var value = try self.pop();
+                    defer value.deinit();
+
+                    const string = &indexed_val.string;
+
+                    const byte = try value.toInteger(u8);
+
+                    const index = try index_val.toInteger(usize);
+                    if (index >= string.contents.len)
+                        return error.IndexOutOfRange;
+
+                    if (string.refcount != null and string.refcount.?.* > 1) {
+                        var new_string = try String.init(self.allocator, string.contents);
+
+                        string.deinit();
+                        string.* = new_string;
+                    }
+                    std.debug.assert(string.refcount == null or string.refcount.?.* == 1);
+
+                    const contents = try string.obtainMutableStorage();
+                    contents[index] = byte;
+                } else {
+                    return error.TypeMismatch;
                 }
 
-                try self.push(array_val);
+                try self.push(indexed_val);
             },
 
             // Iterator Section:
@@ -713,33 +754,6 @@ pub const VM = struct {
         ));
     }
 
-    fn getArrayItem(array_val: *Value, index_val: Value) !*Value {
-        const array = try array_val.getArray();
-        const flt_index = try index_val.toNumber();
-
-        if (flt_index < 0)
-            return error.IndexOutOfRange;
-
-        const index = try floatToInt(usize, std.math.trunc(flt_index));
-        std.debug.assert(index >= 0);
-        if (index >= array.contents.len)
-            return error.IndexOutOfRange;
-
-        return &array.contents[index];
-    }
-
-    fn floatToInt(comptime T: type, flt: anytype) error{Overflow}!T {
-        comptime std.debug.assert(@typeInfo(T) == .Int); // must pass an integer
-        comptime std.debug.assert(@typeInfo(@TypeOf(flt)) == .Float); // must pass a float
-        if (flt > std.math.maxInt(T)) {
-            return error.Overflow;
-        } else if (flt < std.math.minInt(T)) {
-            return error.Overflow;
-        } else {
-            return @floatToInt(T, flt);
-        }
-    }
-
     const SingleResult = enum {
         /// The program has encountered an asynchronous function
         completed,
diff --git a/src/test/behaviour.lola b/src/test/behaviour.lola
index a8571e4..59f5094 100644
--- a/src/test/behaviour.lola
+++ b/src/test/behaviour.lola
@@ -259,4 +259,19 @@ ExpectEqual('💩', 0x1F4A9);
 ExpectEqual('\xF3', 0xF3);
 ExpectEqual('\xf0\x9f\x92\xa9', 0x1F4A9); // handcrafted utf8 escape sequence
 
-Print("Behaviour test suite passed.");
+// String indexing
+ExpectEqual("a"[0], 'a');
+ExpectEqual("ab"[0], 'a');
+ExpectEqual("ab"[1], 'b');
+{
+  var mut = "abc";
+  ExpectEqual(mut, "abc");
+  mut[0] = '1';
+  ExpectEqual(mut, "1bc");
+  mut[1] = '2';
+  ExpectEqual(mut, "12c");
+  mut[2] = '3';
+  ExpectEqual(mut, "123");
+}
+
+Print("Behaviour test suite passed.");
\ No newline at end of file