diff --git a/src/core/fmt.zig b/src/core/fmt.zig
deleted file mode 100644
index 43a0cba..0000000
--- a/src/core/fmt.zig
+++ /dev/null
@@ -1,70 +0,0 @@
-const io = @import("io.zig");
-
-///
-/// Number formatting modes supported by [writeInt].
-///
-pub const Radix = enum {
-    binary,
-    tinary,
-    quaternary,
-    quinary,
-    senary,
-    septenary,
-    octal,
-    nonary,
-    decimal,
-    undecimal,
-    duodecimal,
-    tridecimal,
-    tetradecimal,
-    pentadecimal,
-    hexadecimal,
-};
-
-///
-/// Writes `value` as a ASCII / UTF-8 encoded integer to `writer`, returning `true` if the full
-/// sequence was successfully written, otherwise `false`.
-///
-/// The `radix` argument identifies which base system to format `value` as.
-///
-pub fn printInt(writer: io.Writer, radix: Radix, value: anytype) bool {
-    const Int = @TypeOf(value);
-    const type_info = @typeInfo(Int);
-
-    switch (type_info) {
-        .Int => {
-            if (value == 0) return writer.writeByte('0');
-
-            // TODO: Unhardcode this as it will break with large ints.
-            var buffer = std.mem.zeroes([28]u8);
-            var buffer_count = @as(usize, 0);
-            var n1 = value;
-
-            if ((type_info.Int.signedness == .signed) and (value < 0)) {
-                // Negative value.
-                n1 = -value;
-                buffer[0] = '-';
-                buffer_count += 1;
-            }
-
-            while (n1 != 0) {
-                const base = @enumToInt(radix);
-
-                buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
-                n1 = (n1 / base);
-                buffer_count += 1;
-            }
-
-            for (buffer[0 .. (buffer_count / 2)]) |_, i|
-                std.mem.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
-
-            return (writer.call(.{buffer[0 .. buffer_count]}) == buffer_count);
-        },
-
-        // Cast comptime int into known-size integer and try again.
-        .ComptimeInt => return writer.
-            writeInt(radix, @intCast(std.math.IntFittingRange(value, value), value)),
-
-        else => @compileError("value must be of type int"),
-    }
-}
diff --git a/src/core/io.zig b/src/core/io.zig
index 11c3fa1..495fd7d 100644
--- a/src/core/io.zig
+++ b/src/core/io.zig
@@ -1,11 +1,12 @@
+const math = @import("./math.zig");
 const meta = @import("./meta.zig");
 const stack = @import("./stack.zig");
-const std = @import("std");
+const testing = @import("./testing.zig");
 
 ///
 ///
 ///
-pub const Allocator = std.mem.Allocator;
+pub const Allocator = @import("std").mem.Allocator;
 
 ///
 /// Closure that captures a reference to readable resources like block devices, memory buffers,
@@ -31,6 +32,26 @@ pub fn Spliterator(comptime Element: type) type {
             return (self.source.len != 0);
         }
 
+        test "Check has data" {
+            var empty_spliterator = Spliterator(u8){
+                .source = "",
+                .delimiter = "/",
+            };
+
+            try testing.expect(!empty_spliterator.hasNext());
+
+            var stateful_spliterator = Spliterator(u8){
+                .source = "data",
+                .delimiter = "/",
+            };
+
+            try testing.expect(stateful_spliterator.hasNext());
+
+            _ = try stateful_spliterator.next();
+
+            try testing.expect(!stateful_spliterator.hasNext());
+        }
+
         ///
         /// Iterates on `self` and returns the next view of [Spliterator.source] that matches
         /// [Spliterator.delimiter], or `null` if there is no more data to be processed.
@@ -38,7 +59,11 @@ pub fn Spliterator(comptime Element: type) type {
         pub fn next(self: *Self) ?[]const Element {
             if (!self.hasNext()) return null;
 
-            if (std.mem.indexOfPos(Element, self.source, 0, self.delimiter)) |index| {
+            if (findFirstOf(Element, self.source, self.delimiter, struct {
+                fn testEquality(this: Element, that: Element) bool {
+                    return this == that;
+                }
+            }.testEquality)) |index| {
                 defer self.source = self.source[(index + self.delimiter.len) .. self.source.len];
 
                 return self.source[0 .. index];
@@ -48,43 +73,43 @@ pub fn Spliterator(comptime Element: type) type {
 
             return self.source;
         }
+
+        test "Iterate through data" {
+            // Single-character delimiter.
+            {
+                var spliterator = Spliterator(u8){
+                    .source = "single.character.separated.hello.world",
+                    .delimiter = ".",
+                };
+
+                const components = [_][]const u8{"single",
+                    "character", "separated", "hello", "world"};
+
+                var index = @as(usize, 0);
+
+                while (spliterator.next()) |split| : (index += 1) {
+                    try testing.expect(equals(u8, split, components[index]));
+                }
+            }
+
+            // Multi-character delimiter.
+            {
+                var spliterator = Spliterator(u8){
+                    .source = "finding a needle in a needle stack",
+                    .delimiter = "needle",
+                };
+
+                const components = [_][]const u8{"finding a ", " in a ", " stack"};
+                var index = @as(usize, 0);
+
+                while (spliterator.next()) |split| : (index += 1) {
+                    try testing.expect(equals(u8, split, components[index]));
+                }
+            }
+        }
     };
 }
 
-test "Spliterating text" {
-    const testing = std.testing;
-
-    // Single-character delimiter.
-    {
-        var spliterator = Spliterator(u8){
-            .source = "single.character.separated.hello.world",
-            .delimiter = ".",
-        };
-
-        const components = [_][]const u8{"single", "character", "separated", "hello", "world"};
-        var index = @as(usize, 0);
-
-        while (spliterator.next()) |split| : (index += 1) {
-            try testing.expect(equals(u8, split, components[index]));
-        }
-    }
-
-    // Multi-character delimiter.
-    {
-        var spliterator = Spliterator(u8){
-            .source = "finding a needle in a needle stack",
-            .delimiter = "needle",
-        };
-
-        const components = [_][]const u8{"finding a ", " in a ", " stack"};
-        var index = @as(usize, 0);
-
-        while (spliterator.next()) |split| : (index += 1) {
-            try testing.expect(equals(u8, split, components[index]));
-        }
-    }
-}
-
 ///
 /// Closure that captures a reference to writable resources like block devices, memory buffers,
 /// network sockets, and more.
@@ -102,7 +127,6 @@ pub fn begins(comptime Element: type, elements: []const Element, with: []const E
 
 test "Check memory begins with" {
     const bytes_sequence = &.{69, 42};
-    const testing = std.testing;
 
     try testing.expect(begins(u8, &.{69, 42, 0, 89}, bytes_sequence));
     try testing.expect(!begins(u8, &.{69, 89, 42, 0}, bytes_sequence));
@@ -133,11 +157,9 @@ pub fn bytesOf(pointer: anytype) switch (@typeInfo(@TypeOf(pointer))) {
 }
 
 test "Bytes of types" {
-    const testing = std.testing;
-
     var foo: u32 = 10;
 
-    testing.expectEqual(bytesOf(&foo), 0x0a);
+    try testing.expect(bytesOf(&foo)[0] == 0x0a);
 }
 
 ///
@@ -145,27 +167,38 @@ test "Bytes of types" {
 /// sequences, otherwise `0` if they are identical.
 ///
 pub fn compareBytes(this: []const u8, that: []const u8) isize {
-    var cursor: usize = 0;
+    const range = math.min(usize, this.len, that.len);
+    var index: usize = 0;
 
-    while (cursor != this.len) : (cursor += 1) {
-        const this_byte = this[cursor];
+    while (index < range) : (index += 1) {
+        const difference = (this[index] - that[index]);
 
-        if (cursor != that.len) return this_byte;
-
-        const that_byte = that[cursor];
-
-        if (this_byte != that_byte) return (this_byte - that_byte);
+        if (difference != 0) return difference;
     }
 
-    return 0;
+    return (@intCast(isize, this.len) - @intCast(isize, that.len));
 }
 
 test "Compare bytes" {
-    const testing = std.testing;
+    try testing.expect(compareBytes(&.{69, 42, 0}, &.{69, 42, 0}) == 0);
+    try testing.expect(compareBytes(&.{69, 42, 11}, &.{69, 42}) == 1);
+    try testing.expect(compareBytes(&.{69, 42}, &.{69, 42, 11}) == -1);
+}
 
-    try testing.expectEquals(compareBytes(&.{69, 42, 0}, &.{69, 42, 0}), 0);
-    try testing.expectEquals(compareBytes(&.{69, 42, 0}, &.{69, 42}), 42);
-    try testing.expectEquals(compareBytes(&.{69, 42}, &.{69, 42, 0}), -42);
+///
+/// Copies the contents of `source` into `target`
+///
+pub fn copy(comptime Element: type, target: []Element, source: []const Element) void {
+    for (source) |element, index| target[index] = element;
+}
+
+test "Copy data" {
+    var buffer = [_]u32{0} ** 20;
+    const data = [_]u32{3, 20, 8000};
+
+    copy(u32, &buffer, &data);
+
+    for (data) |datum, index| try testing.expect(buffer[index] == datum);
 }
 
 ///
@@ -175,21 +208,72 @@ test "Compare bytes" {
 pub fn equals(comptime Element: type, this: []const Element, that: []const Element) bool {
     if (this.len != that.len) return false;
 
-    var i = std.mem.zeroes(usize);
+    var index: usize = 0;
 
-    while (i < this.len) : (i += 1) if (this[i] != that[i]) return false;
+    while (index < this.len) : (index += 1) if (this[index] != that[index]) return false;
 
     return true;
 }
 
-test "Check memory is equals" {
+test "Check memory is equal" {
     const bytes_sequence = &.{69, 42, 0};
-    const testing = std.testing;
 
     try testing.expect(equals(u8, bytes_sequence, bytes_sequence));
     try testing.expect(!equals(u8, bytes_sequence, &.{69, 42}));
 }
 
+///
+/// Searches for the first instance of an `Element` equal to `needle` in `haystack`, returning its
+/// index or `null` if nothing was found.
+///
+pub fn findFirst(comptime Element: type, haystack: []const Element,
+    needle: Element, comptime testEquality: fn (Element, Element) bool) ?usize {
+
+    for (haystack) |element, index| if (testEquality(element, needle)) return index;
+
+    return null;
+}
+
+test "Find first of element" {
+    const haystack = &.{"", "", "foo"};
+
+    const testEquality = struct {
+        fn testEquality(this: []const u8, that: []const u8) bool {
+            return equals(u8, this, that);
+        }
+    }.testEquality;
+
+    try testing.expect(findFirst([]const u8, haystack, "foo", testEquality).? == 2);
+    try testing.expect(findFirst([]const u8, haystack, "bar", testEquality) == null);
+}
+
+///
+/// Searches for the first instance of an `Element` sequence equal to the contents of `needle` in
+/// `haystack`, returning the starting index or `null` if nothing was found.
+///
+pub fn findFirstOf(comptime Element: type, haystack: []const Element,
+    needle: []const Element, comptime testEquality: fn (Element, Element) bool) ?usize {
+
+    var cursor: usize = 0;
+    const end = (haystack.len - needle.len);
+
+    walk_haystack: while (cursor <= end) : (cursor += 1) {
+        const range = (cursor + needle.len);
+        var index = cursor;
+
+        while (index < range) : (index += 1)
+            if (testEquality(haystack[index], needle[index])) continue: walk_haystack;
+
+        return cursor;
+    }
+
+    return null;
+}
+
+test "Find first of sequence" {
+
+}
+
 ///
 /// Returns a deterministic hash code compiled from each byte in `bytes`.
 ///
@@ -205,12 +289,30 @@ pub fn hashBytes(bytes: []const u8) usize {
 
 test "Hashing bytes" {
     const bytes_sequence = &.{69, 42, 0};
-    const testing = std.testing;
 
     try testing.expect(hashBytes(bytes_sequence) == hashBytes(bytes_sequence));
     try testing.expect(hashBytes(bytes_sequence) != hashBytes(&.{69, 42}));
 }
 
+///
+/// Swaps the `Data` in `this` with `that`.
+///
+pub fn swap(comptime Data: type, this: *Data, that: *Data) void {
+    const temp = this.*;
+    this.* = that.*;
+    that.* = temp;
+}
+
+test "Data swapping" {
+    var a: u64 = 0;
+    var b: u64 = 1;
+
+    swap(u64, &a, &b);
+
+    try testing.expect(a == 1);
+    try testing.expect(b == 0);
+}
+
 ///
 /// Returns a [Writer] that silently consumes all given data without failure and throws it away.
 ///
@@ -218,7 +320,7 @@ test "Hashing bytes" {
 /// sent somewhere for whatever reason.
 ///
 pub fn nullWriter() Writer {
-    return Writer.capture(std.mem.zeroes(usize), struct {
+    return Writer.capture(@as(usize, 0), struct {
         fn write(_: usize, buffer: []const u8) usize {
             return buffer.len;
         }
@@ -226,11 +328,7 @@ pub fn nullWriter() Writer {
 }
 
 test "Null writing" {
-    const testing = std.testing;
+    const sequence = "foo";
 
-    {
-        const sequence = "foo";
-
-        try testing.expectEqual(nullWriter().apply(sequence), sequence.len);
-    }
+    try testing.expect(nullWriter().call(sequence) == sequence.len);
 }
diff --git a/src/core/main.zig b/src/core/main.zig
index 602ea7b..785b8e5 100644
--- a/src/core/main.zig
+++ b/src/core/main.zig
@@ -5,12 +5,17 @@
 pub const io = @import("./io.zig");
 
 ///
-/// Metaprogramming introspection and generation utilities.
+/// Math types and functions with a focus on graphics-specific linear algebra.
+///
+pub const math = @import("./math.zig");
+
+///
+/// Metaprogramming introspection and generation.
 ///
 pub const meta = @import("./meta.zig");
 
 ///
-/// Sequential last-in first-out data structures.
+/// Sequential, last-in first-out data structures.
 ///
 pub const stack = @import("./stack.zig");
 
@@ -19,9 +24,22 @@ pub const stack = @import("./stack.zig");
 ///
 pub const table = @import("./table.zig");
 
+///
+/// Unit testing suite utilities.
+///
+pub const testing = @import("./testing.zig");
+
+///
+/// Unicode-encoded string analysis and processing with a focus on UTF-8 encoded text.
+///
+pub const unicode = @import("./unicode.zig");
+
 test {
     _ = io;
+    _ = math;
     _ = meta;
     _ = stack;
     _ = table;
+    _ = testing;
+    _ = unicode;
 }
diff --git a/src/core/math.zig b/src/core/math.zig
new file mode 100644
index 0000000..e6f9959
--- /dev/null
+++ b/src/core/math.zig
@@ -0,0 +1,26 @@
+
+pub const IntFittingRange = @import("std").math.IntFittingRange;
+
+///
+/// Returns the maximum value of `Integer`.
+///
+pub fn maxInt(comptime Integer: type) Integer {
+    return switch (@typeInfo(Integer)) {
+        .Int => |info| if (info.bits == 0) 0 else
+            ((1 << (info.bits - @boolToInt(info.signedness == .signed))) - 1),
+
+        else => @compileError("`" ++ @typeName(Integer) ++ "` must be an int"),
+    };
+}
+
+///
+/// Returns the lowest `Number` value between `this` and `that`.
+///
+pub fn min(comptime Number: type, this: Number, that: Number) Number {
+    return switch (@typeInfo(Number)) {
+        .Int, .Float, .ComptimeInt, .ComptimeFloat => if (this < that) this else that,
+
+        else => @compileError("`" ++ @typeName(Number) ++
+            "` must be an int, float, comptime_int, or comptime_float"),
+    };
+}
diff --git a/src/core/meta.zig b/src/core/meta.zig
index f76f362..e7be22d 100644
--- a/src/core/meta.zig
+++ b/src/core/meta.zig
@@ -1,5 +1,3 @@
-const std = @import("std");
-
 ///
 /// Returns the return type of the function type `Fn`.
 ///
@@ -11,70 +9,13 @@ pub fn FnReturn(comptime Fn: type) type {
     return type_info.Fn.return_type orelse void;
 }
 
-///
-/// Returns a double-input single-output closure type where `A` represents the first input type, `B`
-/// represents the second, and `Out` represents the output type, and `captures_size` represents the
-/// size of the closure context.
-///
-pub fn BiFunction(comptime captures_size: usize, comptime A: type,
-    comptime B: type, comptime Out: type) type {
-
-    return struct {
-        applyErased: fn (*anyopaque, A, B) Out,
-        context: [captures_size]u8,
-
-        ///
-        /// Function type.
-        ///
-        const Self = @This();
-
-        ///
-        /// Applies `a` and `b` to `self`, producing a result according to the current context data.
-        ///
-        pub fn apply(self: *Self, a: A, b: B) Out {
-            return self.applyErased(&self.context, a, b);
-        }
-
-        ///
-        /// Creates a new [Self] by capturing the `captures` value as the context and `call` as the
-        /// as the behavior executed when [apply] or [applyErased] is called.
-        ///
-        /// The newly created [Self] is returned.
-        ///
-        pub fn capture(captures: anytype, comptime call: fn (@TypeOf(captures), A, B) Out) Self {
-            const Captures = @TypeOf(captures);
-
-            if (@sizeOf(Captures) > captures_size)
-                @compileError("`captures` must be smaller than or equal to " ++
-                    std.fmt.comptimePrint("{d}", .{captures_size}) ++ " bytes");
-
-            var function = Self{
-                .context = undefined,
-
-                .applyErased = struct {
-                    fn applyErased(erased: *anyopaque, a: A, b: B) Out {
-                        return call(if (Captures == void) {} else @ptrCast(*Captures,
-                            @alignCast(@alignOf(Captures), erased)).*, a, b);
-                    }
-                }.applyErased,
-            };
-
-            if (captures != {}) {
-                @ptrCast(*Captures, @alignCast(@alignOf(Captures), &function.context)).* = captures;
-            }
-
-            return function;
-        }
-    };
-}
-
 ///
 /// Returns a single-input single-output closure type where `In` represents the input type, `Out`
 /// represents the output type, and `captures_size` represents the size of the closure context.
 ///
 pub fn Function(comptime captures_size: usize, comptime In: type, comptime Out: type) type {
     return struct {
-        applyErased: fn (*anyopaque, In) Out,
+        callErased: fn (*anyopaque, In) Out,
         context: [captures_size]u8,
 
         ///
@@ -83,39 +24,39 @@ pub fn Function(comptime captures_size: usize, comptime In: type, comptime Out:
         const Self = @This();
 
         ///
-        /// Applies `input` to `self`, producing a result according to the current context data.
+        /// Invokes `self` with `input`, producing a result according to the current context data.
         ///
-        pub fn apply(self: *Self, input: In) Out {
-            return self.applyErased(&self.context, input);
+        pub fn call(self: *Self, input: In) Out {
+            return self.callErased(&self.context, input);
         }
 
         ///
-        /// Creates a new [Self] by capturing the `captures` value as the context and `call` as the
-        /// as the behavior executed when [apply] or [applyErased] is called.
+        /// Creates a new [Self] by capturing the `captures` value as the context and `invoke` as
+        /// the as the behavior executed when [call] or [callErased] is called.
         ///
         /// The newly created [Self] is returned.
         ///
-        pub fn capture(captures: anytype, comptime call: fn (@TypeOf(captures), In) Out) Self {
+        pub fn capture(captures: anytype, comptime invoke: fn (@TypeOf(captures), In) Out) Self {
             const Captures = @TypeOf(captures);
 
             if (@sizeOf(Captures) > captures_size)
-                @compileError("`captures` must be smaller than or equal to " ++
-                    std.fmt.comptimePrint("{d}", .{captures_size}) ++ " bytes");
+                @compileError("`captures` exceeds the size limit of the capture context");
 
             const captures_align = @alignOf(Captures);
 
             var function = Self{
                 .context = undefined,
 
-                .applyErased = struct {
-                    fn applyErased(erased: *anyopaque, input: In) Out {
-                        return call(if (Captures == void) {} else @ptrCast(*Captures,
+                .callErased = struct {
+                    fn callErased(erased: *anyopaque, input: In) Out {
+                        return invoke(if (Captures == void) {} else @ptrCast(*Captures,
                             @alignCast(@alignOf(Captures), erased)).*, input);
                     }
-                }.applyErased,
+                }.callErased,
             };
 
-            @ptrCast(*Captures, @alignCast(captures_align, &function.context)).* = captures;
+            if (Captures != void)
+                @ptrCast(*Captures, @alignCast(captures_align, &function.context)).* = captures;
 
             return function;
         }
diff --git a/src/core/stack.zig b/src/core/stack.zig
index 77a4e01..6caa0fb 100755
--- a/src/core/stack.zig
+++ b/src/core/stack.zig
@@ -1,5 +1,5 @@
 const io = @import("./io.zig");
-const std = @import("std");
+const testing = @import("./testing.zig");
 
 ///
 /// Returns a fixed-size stack type of `Element`s.
@@ -15,42 +15,20 @@ pub fn Fixed(comptime Element: type) type {
         const Self = @This();
 
         ///
-        /// Wraps `self` and returns it in a [io.Writer] value.
-        ///
-        /// Note that this will raise a compilation error if [Element] is not `u8`.
-        ///
-        pub fn writer(self: *Self) io.Writer {
-            if (Element != u8) @compileError("Cannot coerce fixed stack of type " ++
-                @typeName(Element) ++ " into a Writer");
-
-            return io.Writer.capture(self, struct {
-                fn write(stack: *Self, buffer: []const u8) usize {
-                    stack.pushAll(buffer) catch |err| switch (err) {
-                        error.OutOfMemory => return 0,
-                    };
-
-                    return buffer.len;
-                }
-            }.write);
-        }
-
-        ///
-        /// Clears all elements from `self`.
+        /// Resets the number of filled items to `0`, otherwise leaving the actual memory contents
+        /// of the buffer untouched until it is later overwritten by following operations on it.
         ///
         pub fn clear(self: *Self) void {
             self.filled = 0;
         }
 
         ///
-        /// Counts and returns the number of pushed elements in `self`.
+        /// If `self` is filled with at least `1` value, it is decremented by `1`, otherwise leaving
+        /// the actual memory contents of the buffer untouched until it is later overwritten by
+        /// following operations on it.
         ///
-        pub fn count(self: Self) usize {
-            return self.filled;
-        }
-
-        ///
-        /// Attempts to pop the tail-end of `self`, returning the element value or `null` if the
-        /// stack is empty.
+        /// The value of the element removed from the list is returned if something existed to be
+        /// popped, otherwise `null` if it contained no elements.
         ///
         pub fn pop(self: *Self) ?Element {
             if (self.filled == 0) return null;
@@ -74,40 +52,92 @@ pub fn Fixed(comptime Element: type) type {
         /// Attempts to push all of `elements` into `self`, returning a [FixedPushError] if it
         /// failed.
         ///
-        pub fn pushAll(self: *Self, elements: []const u8) PushError!void {
+        pub fn pushAll(self: *Self, elements: []const Element) PushError!void {
             const filled = (self.filled + elements.len);
 
             if (filled > self.buffer.len) return error.OutOfMemory;
 
-            std.mem.copy(u8, self.buffer[self.filled ..], elements);
+            io.copy(Element, self.buffer[self.filled ..], elements);
 
             self.filled = filled;
         }
     };
 }
 
+test "Fixed stack of string literals" {
+    const default_value = "";
+    var buffer = [_][]const u8{default_value} ** 4;
+    var shopping_list = Fixed([]const u8){.buffer = &buffer};
+
+    // Pop empty stack.
+    {
+        try testing.expect(shopping_list.pop() == null);
+        try testing.expect(shopping_list.filled == 0);
+        try testing.expect(shopping_list.buffer.ptr == &buffer);
+        try testing.expect(shopping_list.buffer.len == buffer.len);
+
+        for (shopping_list.buffer) |item|
+            try testing.expect(io.equals(u8, item, default_value));
+    }
+
+    // Push single element.
+    {
+        try shopping_list.push("milk");
+        try testing.expect(shopping_list.filled == 1);
+        try testing.expect(shopping_list.buffer.ptr == &buffer);
+        try testing.expect(shopping_list.buffer.len == buffer.len);
+        try testing.expect(io.equals(u8, shopping_list.buffer[0], "milk"));
+
+        for (shopping_list.buffer[1 ..]) |item|
+            try testing.expect(io.equals(u8, item, default_value));
+
+        // TODO: Test stack overflow.
+    }
+
+    // Pop single element.
+    {
+        try testing.expect(io.equals(u8, shopping_list.pop().?, "milk"));
+        try testing.expect(shopping_list.filled == 0);
+        try testing.expect(shopping_list.buffer.ptr == &buffer);
+        try testing.expect(shopping_list.buffer.len == buffer.len);
+        try testing.expect(io.equals(u8, shopping_list.buffer[0], "milk"));
+
+        for (shopping_list.buffer[1 ..]) |item|
+            try testing.expect(io.equals(u8, item, default_value));
+    }
+
+    // TODO: Multiple elements.
+    // TODO: Clear elements.
+}
+
 ///
 /// Potential errors that may occur while trying to push one or more elements into a stack.
 ///
-pub const PushError = std.mem.Allocator.Error;
+pub const PushError = io.Allocator.Error;
 
-test "Fixed stack manipulation" {
-    const testing = std.testing;
-    var buffer = std.mem.zeroes([4]u8);
-    var stack = Fixed(u8){.buffer = &buffer};
+///
+/// Returns an [io.Writer] wrapping `fixed_stack`.
+///
+/// Writing to the returned [io.Writer] will push values to the underlying [Fixed] stack instance
+/// referenced by `fixed_stack` until it is full.
+///
+pub fn fixedWriter(fixed_stack: *Fixed(u8)) io.Writer {
+    return io.Writer.capture(fixed_stack, struct {
+        fn write(stack: *Fixed(u8), buffer: []const u8) usize {
+            stack.pushAll(buffer) catch |err| switch (err) {
+                error.OutOfMemory => return 0,
+            };
 
-    try testing.expectEqual(stack.count(), 0);
-    try testing.expectEqual(stack.pop(), null);
-    try stack.push(69);
-    try testing.expectEqual(stack.count(), 1);
-    try testing.expectEqual(stack.pop(), 69);
-    try stack.pushAll(&.{42, 10, 95, 0});
-    try testing.expectEqual(stack.count(), 4);
-    try testing.expectError(PushError.OutOfMemory, stack.push(1));
-    try testing.expectError(PushError.OutOfMemory, stack.pushAll(&.{1, 11, 11}));
-
-    stack.clear();
-
-    try testing.expectEqual(stack.count(), 0);
-    try testing.expectEqual(stack.writer().apply(&.{0, 0, 0, 0}), 4);
+            return buffer.len;
+        }
+    }.write);
+}
+
+test "Fixed writer" {
+    var buffer = [_]u8{0} ** 4;
+    var sequence_stack = Fixed(u8){.buffer = &buffer};
+    const sequence_data = [_]u8{8, 16, 32, 64};
+
+    try testing.expect(fixedWriter(&sequence_stack).call(&sequence_data) == sequence_data.len);
+    try testing.expect(io.equals(u8, sequence_stack.buffer, &sequence_data));
 }
diff --git a/src/core/testing.zig b/src/core/testing.zig
new file mode 100644
index 0000000..1881378
--- /dev/null
+++ b/src/core/testing.zig
@@ -0,0 +1,18 @@
+///
+/// [TestError.UnexpectedResult] occurs when a conditional that should have been `true` was actually
+/// `false`.
+///
+pub const TestError = error {
+    UnexpectedResult,
+};
+
+///
+/// Returns a [TestError] if `ok` is false.
+///
+pub fn expect(ok: bool) TestError!void {
+    if (!ok) return error.UnexpectedResult;
+}
+
+// TODO: Implement tests.
+
+pub const expectError = @import("std").testing.expectError;
diff --git a/src/core/unicode.zig b/src/core/unicode.zig
new file mode 100644
index 0000000..6e89678
--- /dev/null
+++ b/src/core/unicode.zig
@@ -0,0 +1,84 @@
+const io = @import("./io.zig");
+const math = @import("./math.zig");
+
+///
+/// [PrintError.WriteFailure] occurs when the underlying [io.Writer] implementation failed to write
+/// the entirety of a the requested print operation.
+///
+pub const PrintError = error {
+    WriteFailure,
+};
+
+///
+/// Number formatting modes supported by [printInt].
+///
+pub const Radix = enum {
+    binary,
+    tinary,
+    quaternary,
+    quinary,
+    senary,
+    septenary,
+    octal,
+    nonary,
+    decimal,
+    undecimal,
+    duodecimal,
+    tridecimal,
+    tetradecimal,
+    pentadecimal,
+    hexadecimal,
+};
+
+///
+/// Writes `value` as a ASCII / UTF-8 encoded integer to `writer`, returning `true` if the full
+/// sequence was successfully written, otherwise `false`.
+///
+/// The `radix` argument identifies which base system to format `value` as.
+///
+pub fn printInt(writer: io.Writer, radix: Radix, value: anytype) PrintError!void {
+    const Int = @TypeOf(value);
+
+    switch (@typeInfo(Int)) {
+        .Int => |int_info| {
+            if (value == 0) return writer.apply("0");
+
+            const base = @enumToInt(radix);
+            const is_signed = (int_info.signedness == .signed);
+
+            var buffer = [_]u8{0} ** (math.ceil(math.log(math.
+                maxInt(Int), base)) + @boolToInt(is_signed));
+
+            var buffer_count: usize = 0;
+            var n1 = value;
+
+            if (is_signed and (value < 0)) {
+                // Negative value.
+                n1 = -value;
+                buffer[0] = '-';
+                buffer_count += 1;
+            }
+
+            while (n1 != 0) {
+                buffer[buffer_count] = @intCast(u8, (n1 % base) + '0');
+                n1 = (n1 / base);
+                buffer_count += 1;
+            }
+
+            for (buffer[0 .. (buffer_count / 2)]) |_, i|
+                io.swap(u8, &buffer[i], &buffer[buffer_count - i - 1]);
+
+            if (writer.call(buffer[0 .. buffer_count]) != buffer_count) return error.WriteFailure;
+        },
+
+        // Cast comptime int into known-size integer and try again.
+        .ComptimeInt => return printInt(writer, radix,
+            @intCast(math.IntFittingRange(value, value), value)),
+
+        else => @compileError("`value` must be of type int or comptime_int"),
+    }
+}
+
+test "Print 64-bit signed integer" {
+    // TODO: implement.
+}