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<title>Extra Credit: Write a Tree-Shaker · Learn Lisp The Hard Way</title>
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<li class="header">LEARN LISP THE HARD WAY</li>
<li class="chapter " data-level="1.1" data-path="./">
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Second Draft (in-progress)
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CHANGELOG
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TODO
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<li class="header">PREFACE</li>
<li class="chapter " data-level="2.1" data-path="preface.html">
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TANSTAAFL
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The Hard Way is Easier
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Who Is This Book For?
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<li class="chapter " data-level="2.4" data-path="introduction.html">
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Lisp: A Future History
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<li class="chapter " data-level="2.5" data-path="acknowledgements.html">
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Acknowledgements
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<li class="header">PART ONE</li>
<li class="chapter " data-level="3.1" data-path="1-0-0-overview.html">
<a href="1-0-0-overview.html">
Grokking Lisp
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<ul class="articles">
<li class="chapter " data-level="3.1.1" data-path="1-01-00-lisp-bootcamp.html">
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Common Lisp Bootcamp
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<li class="chapter " data-level="3.1.1.1" data-path="1-01-01-syntax-overview.html">
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Syntax Overview in 5 Minutes
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<li class="chapter " data-level="3.1.1.2" data-path="1-01-02-repl.html">
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The REPL
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<li class="chapter " data-level="3.1.1.3" data-path="1-01-03-expressions.html">
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Expressions, Parentheses, and Return Values
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<li class="chapter " data-level="3.1.1.4" data-path="1-01-04-lists-cons-cells.html">
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Lists, Cons-Cells, and Memory
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<li class="chapter " data-level="3.1.1.5" data-path="1-01-05-symbols.html">
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Symbols and Namespaces
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<li class="chapter " data-level="3.1.1.6" data-path="1-01-06-prefix-notation.html">
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Prefix Notation
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<li class="chapter " data-level="3.1.1.7" data-path="1-01-07-style-guide.html">
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Common Lisp Style Guide
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<li class="chapter " data-level="3.1.1.8" data-path="1-01-08-configuration.html">
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Configuring Your Development Environment
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</ul>
</li>
<li class="chapter " data-level="3.1.2" data-path="1-02-00-input-output.html">
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Printing, Streams, and Strings
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<li class="chapter " data-level="3.1.2.1" data-path="1-02-01-strings.html">
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Strings
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<li class="chapter " data-level="3.1.2.2" data-path="1-02-02-more-strings.html">
<a href="1-02-02-more-strings.html">
More Strings
</a>
</li>
<li class="chapter " data-level="3.1.2.3" data-path="1-02-03-unicode.html">
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Unicode and Strings
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</li>
<li class="chapter " data-level="3.1.2.4" data-path="1-02-04-chars.html">
<a href="1-02-04-chars.html">
Characters
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</li>
<li class="chapter " data-level="3.1.2.5" data-path="1-02-05-more-chars.html">
<a href="1-02-05-more-chars.html">
More Characters
</a>
</li>
<li class="chapter " data-level="3.1.2.6" data-path="1-02-06-char-codes.html">
<a href="1-02-06-char-codes.html">
Character Codes
</a>
</li>
<li class="chapter " data-level="3.1.2.7" data-path="1-02-07-strings-from-chars.html">
<a href="1-02-07-strings-from-chars.html">
Strings from Chars
</a>
</li>
<li class="chapter " data-level="3.1.2.8" data-path="1-02-08-printing.html">
<a href="1-02-08-printing.html">
Printing
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</li>
<li class="chapter " data-level="3.1.2.9" data-path="1-02-09-more-printing.html">
<a href="1-02-09-more-printing.html">
More Printing
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<li class="chapter " data-level="3.1.2.10" data-path="1-02-10-prin1.html">
<a href="1-02-10-prin1.html">
Printing With prin1
</a>
</li>
<li class="chapter " data-level="3.1.2.11" data-path="1-02-11-princ.html">
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Printing With princ
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<li class="chapter " data-level="3.1.2.12" data-path="1-02-12-format.html">
<a href="1-02-12-format.html">
A Brief Introduction to Format
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<li class="chapter " data-level="3.1.2.13" data-path="1-02-13-more-format.html">
<a href="1-02-13-more-format.html">
A Little Bit More on Format
</a>
</li>
<li class="chapter " data-level="3.1.2.14" data-path="1-02-14-pathnames.html">
<a href="1-02-14-pathnames.html">
Pathnames
</a>
</li>
<li class="chapter " data-level="3.1.2.15" data-path="1-02-15-streams.html">
<a href="1-02-15-streams.html">
Streams
</a>
</li>
<li class="chapter " data-level="3.1.2.16" data-path="1-02-16-file-streams.html">
<a href="1-02-16-file-streams.html">
File Streams
</a>
</li>
<li class="chapter " data-level="3.1.2.17" data-path="1-02-17-binary-streams.html">
<a href="1-02-17-binary-streams.html">
Binary Streams
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<li class="chapter " data-level="3.1.2.18" data-path="1-02-18-prompting-users.html">
<a href="1-02-18-prompting-users.html">
Prompting Users
</a>
</li>
<li class="chapter " data-level="3.1.2.19" data-path="1-02-19-pretty-printing.html">
<a href="1-02-19-pretty-printing.html">
Pretty-Printing
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</ul>
</li>
<li class="chapter " data-level="3.1.3" data-path="1-03-0-getting-input-from-users.html">
<a href="1-03-0-getting-input-from-users.html">
Extra Credit: Getting Input from Users
</a>
</li>
<li class="chapter " data-level="3.1.4" data-path="1-04-0-lists.html">
<a href="1-04-0-lists.html">
Lists and List-Operations
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</li>
<li class="chapter " data-level="3.1.5" data-path="1-05-0-lookups-trees.html">
<a href="1-05-0-lookups-trees.html">
Extra Credit: Look-up Lists and Trees
</a>
</li>
<li class="chapter " data-level="3.1.6" data-path="1-06-0-math.html">
<a href="1-06-0-math.html">
Numbers and Math
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<ul class="articles">
<li class="chapter " data-level="3.1.6.1" data-path="1-06-01-integers.html">
<a href="1-06-01-integers.html">
Integers
</a>
</li>
<li class="chapter " data-level="3.1.6.2" data-path="1-06-02-more-integers.html">
<a href="1-06-02-more-integers.html">
More Integers
</a>
</li>
<li class="chapter " data-level="3.1.6.3" data-path="1-06-03-hexadecimal-notation.html">
<a href="1-06-03-hexadecimal-notation.html">
Hexadecimal Integer Notation
</a>
</li>
<li class="chapter " data-level="3.1.6.4" data-path="1-06-04-octal-notation.html">
<a href="1-06-04-octal-notation.html">
Octal Integer Notation
</a>
</li>
<li class="chapter " data-level="3.1.6.5" data-path="1-06-05-binary-notation.html">
<a href="1-06-05-binary-notation.html">
Binary Integer Notation
</a>
</li>
<li class="chapter " data-level="3.1.6.6" data-path="1-06-06-ratios.html">
<a href="1-06-06-ratios.html">
Ratios and Rational Numbers
</a>
</li>
<li class="chapter " data-level="3.1.6.7" data-path="1-06-07-floating-point.html">
<a href="1-06-07-floating-point.html">
Floating-point Numbers
</a>
</li>
<li class="chapter " data-level="3.1.6.8" data-path="1-06-08-constants.html">
<a href="1-06-08-constants.html">
Numeric Constants
</a>
</li>
<li class="chapter " data-level="3.1.6.9" data-path="1-06-09-complex-numbers.html">
<a href="1-06-09-complex-numbers.html">
Complex Numbers
</a>
</li>
<li class="chapter " data-level="3.1.6.10" data-path="1-06-10-arithmetic.html">
<a href="1-06-10-arithmetic.html">
Arithmetic
</a>
</li>
<li class="chapter " data-level="3.1.6.11" data-path="1-06-11-more-arithmetic.html">
<a href="1-06-11-more-arithmetic.html">
More Arithmetic
</a>
</li>
<li class="chapter " data-level="3.1.6.12" data-path="1-06-12-even-more-arithmetic.html">
<a href="1-06-12-even-more-arithmetic.html">
Even More Arithmetic
</a>
</li>
<li class="chapter " data-level="3.1.6.13" data-path="1-06-13-exponents.html">
<a href="1-06-13-exponents.html">
Exponents
</a>
</li>
<li class="chapter " data-level="3.1.6.14" data-path="1-06-14-logarithms.html">
<a href="1-06-14-logarithms.html">
Logarithms
</a>
</li>
<li class="chapter " data-level="3.1.6.15" data-path="1-06-15-trigonometry.html">
<a href="1-06-15-trigonometry.html">
Trigonometry
</a>
</li>
<li class="chapter " data-level="3.1.6.16" data-path="1-06-16-psuedorandom-numbers.html">
<a href="1-06-16-psuedorandom-numbers.html">
Pseudo-Random Numbers
</a>
</li>
</ul>
</li>
<li class="chapter " data-level="3.1.7" data-path="1-07-0-arrays.html">
<a href="1-07-0-arrays.html">
Extra Credit: Arrays and Vectors
</a>
</li>
<li class="chapter " data-level="3.1.8" data-path="1-08-0-variables.html">
<a href="1-08-0-variables.html">
Variables, Parameters, and Constants
</a>
</li>
<li class="chapter " data-level="3.1.9" data-path="1-09-0-closures.html">
<a href="1-09-0-closures.html">
Extra Credit: Closures
</a>
</li>
<li class="chapter " data-level="3.1.10" data-path="1-10-0-functions.html">
<a href="1-10-0-functions.html">
Functions and Macros
</a>
</li>
<li class="chapter " data-level="3.1.11" data-path="1-11-0-text-adventure.html">
<a href="1-11-0-text-adventure.html">
Extra Credit: A Simple Text Adventure
</a>
</li>
<li class="chapter " data-level="3.1.12" data-path="1-12-0-namespaces.html">
<a href="1-12-0-namespaces.html">
Namespaces, Symbols, Packages, and Systems
</a>
</li>
<li class="chapter " data-level="3.1.13" data-path="1-13-0-simple-web-app.html">
<a href="1-13-0-simple-web-app.html">
Extra Credit: A Simple Web Application
</a>
</li>
<li class="chapter " data-level="3.1.14" data-path="1-14-0-conditionals.html">
<a href="1-14-0-conditionals.html">
Conditionals
</a>
</li>
<li class="chapter " data-level="3.1.15" data-path="1-15-0-command-line-utility.html">
<a href="1-15-0-command-line-utility.html">
Extra Credit: Command-Line Utilities
</a>
</li>
<li class="chapter " data-level="3.1.16" data-path="1-16-0-map-loop.html">
<a href="1-16-0-map-loop.html">
Mapping and Looping
</a>
</li>
<li class="chapter " data-level="3.1.17" data-path="1-17-0-iterate.html">
<a href="1-17-0-iterate.html">
Extra Credit: Revisiting Loops with Iterate
</a>
</li>
<li class="chapter " data-level="3.1.18" data-path="1-18-0-format.html">
<a href="1-18-0-format.html">
Format Strings
</a>
</li>
<li class="chapter " data-level="3.1.19" data-path="1-19-0-dsl.html">
<a href="1-19-0-dsl.html">
Extra Credit: Domain Specific Languages
</a>
</li>
<li class="chapter " data-level="3.1.20" data-path="1-20-0-review.html">
<a href="1-20-0-review.html">
Part One in Review
</a>
</li>
</ul>
</li>
<li class="header">PART TWO</li>
<li class="chapter " data-level="4.1" data-path="2-0-0-overview.html">
<a href="2-0-0-overview.html">
The Suffusion of Blue
</a>
<ul class="articles">
<li class="chapter " data-level="4.1.1" data-path="2-01-0-programming-paradigms.html">
<a href="2-01-0-programming-paradigms.html">
Programming Paradigms
</a>
</li>
<li class="chapter " data-level="4.1.2" data-path="2-02-0-regex.html">
<a href="2-02-0-regex.html">
Extra Credit: Regular Expressions
</a>
</li>
<li class="chapter " data-level="4.1.3" data-path="2-03-0-objects-control.html">
<a href="2-03-0-objects-control.html">
Objects and Control Structures
</a>
</li>
<li class="chapter " data-level="4.1.4" data-path="2-04-0-data-persistence.html">
<a href="2-04-0-data-persistence.html">
Extra Credit: Persistence and Databases
</a>
</li>
<li class="chapter " data-level="4.1.5" data-path="2-05-0-extended-types.html">
<a href="2-05-0-extended-types.html">
Extended Types
</a>
</li>
<li class="chapter " data-level="4.1.6" data-path="2-06-0-threads-memos-parallel.html">
<a href="2-06-0-threads-memos-parallel.html">
Extra Credit: Concurrency and Memoization
</a>
</li>
<li class="chapter " data-level="4.1.7" data-path="2-07-0-logic-and-more-math.html">
<a href="2-07-0-logic-and-more-math.html">
Logic and Advanced Math
</a>
</li>
<li class="chapter " data-level="4.1.8" data-path="2-08-0-number-theory.html">
<a href="2-08-0-number-theory.html">
Extra Credit: Number Theory
</a>
</li>
<li class="chapter " data-level="4.1.9" data-path="2-09-0-binary-octets-bits.html">
<a href="2-09-0-binary-octets-bits.html">
Binary Streams, Octet-Vectors, and Bit-Vectors
</a>
</li>
<li class="chapter " data-level="4.1.10" data-path="2-10-0-improved-text-adventure-engine.html">
<a href="2-10-0-improved-text-adventure-engine.html">
Extra Credit: An Improved Text Adventure Engine
</a>
</li>
<li class="chapter " data-level="4.1.11" data-path="2-11-0-conditions.html">
<a href="2-11-0-conditions.html">
Conditions and Error Handling
</a>
</li>
<li class="chapter " data-level="4.1.12" data-path="2-12-0-2d-game.html">
<a href="2-12-0-2d-game.html">
Extra Credit: Write a 2D Game
</a>
</li>
<li class="chapter " data-level="4.1.13" data-path="2-13-0-compiler.html">
<a href="2-13-0-compiler.html">
The Compiler
</a>
</li>
<li class="chapter active" data-level="4.1.14" data-path="2-14-0-tree-shaker.html">
<a href="2-14-0-tree-shaker.html">
Extra Credit: Write a Tree-Shaker
</a>
</li>
<li class="chapter " data-level="4.1.15" data-path="2-15-0-docs-and-inspection.html">
<a href="2-15-0-docs-and-inspection.html">
Documentation and Inspection
</a>
</li>
<li class="chapter " data-level="4.1.16" data-path="2-16-0-foreign-libs.html">
<a href="2-16-0-foreign-libs.html">
Extra Credit: Foreign Libraries in Lisp
</a>
</li>
<li class="chapter " data-level="4.1.17" data-path="2-17-0-debugging-testing.html">
<a href="2-17-0-debugging-testing.html">
Debugging and Unit Testing
</a>
</li>
<li class="chapter " data-level="4.1.18" data-path="2-18-0-ffi.html">
<a href="2-18-0-ffi.html">
Extra Credit: Write a Foreign Function Interface
</a>
</li>
<li class="chapter " data-level="4.1.19" data-path="2-19-0-essential-libs.html">
<a href="2-19-0-essential-libs.html">
Essential Lisp Libraries
</a>
</li>
<li class="chapter " data-level="4.1.20" data-path="2-20-0-packaging-libs.html">
<a href="2-20-0-packaging-libs.html">
Extra Credit: Packaging Lisp Libraries
</a>
</li>
<li class="chapter " data-level="4.1.21" data-path="2-21-0-review.html">
<a href="2-21-0-review.html">
Detailed Syntax Review
</a>
</li>
</ul>
</li>
<li class="header">PART THREE</li>
<li class="chapter " data-level="5.1" data-path="3-00-00-overview.html">
<a href="3-00-00-overview.html">
Lisp So(u)rcery
</a>
<ul class="articles">
<li class="chapter " data-level="5.1.1" data-path="3-01-00-web-apps.html">
<a href="3-01-00-web-apps.html">
Real-world Web Apps
</a>
</li>
<li class="chapter " data-level="5.1.2" data-path="3-02-00-typesetting.html">
<a href="3-02-00-typesetting.html">
Typesetting
</a>
</li>
<li class="chapter " data-level="5.1.3" data-path="3-03-00-mobile.html">
<a href="3-03-00-mobile.html">
Native Mobile Applications
</a>
</li>
<li class="chapter " data-level="5.1.4" data-path="3-04-00-gui.html">
<a href="3-04-00-gui.html">
Cross-platform Desktop Applications
</a>
</li>
<li class="chapter " data-level="5.1.5" data-path="3-05-00-system-utils.html">
<a href="3-05-00-system-utils.html">
Drivers, Daemons, and System-Utilities
</a>
</li>
<li class="chapter " data-level="5.1.6" data-path="3-06-00-reverse-engineering.html">
<a href="3-06-00-reverse-engineering.html">
Reverse Engineering
</a>
</li>
<li class="chapter " data-level="5.1.7" data-path="3-07-00-graphics.html">
<a href="3-07-00-graphics.html">
Graphics Rendering
</a>
</li>
<li class="chapter " data-level="5.1.8" data-path="3-08-00-gaming.html">
<a href="3-08-00-gaming.html">
OpenGL, SDL, and 3D Game Development
</a>
</li>
<li class="chapter " data-level="5.1.9" data-path="3-09-00-audio.html">
<a href="3-09-00-audio.html">
Audio Generation and Manipulation
</a>
</li>
<li class="chapter " data-level="5.1.10" data-path="3-10-00-data.html">
<a href="3-10-00-data.html">
Data Aggregation and Analysis
</a>
</li>
<li class="chapter " data-level="5.1.11" data-path="3-11-00-cryptosec.html">
<a href="3-11-00-cryptosec.html">
Cryptography and Security
</a>
</li>
<li class="chapter " data-level="5.1.12" data-path="3-12-00-fintech.html">
<a href="3-12-00-fintech.html">
Financial Software and Crypto-Currencies
</a>
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<h1 id="chapter-214-----extra-credit">Chapter 2.14 --- Extra Credit</h1>
<h2 id="write-a-tree-shaker">Write a Tree-Shaker</h2>
<blockquote>
<p>&quot;Whatever the answers are, here&apos;s one monkey that&apos;s going to keep on climbing, and looking around him to see what he can see, as long as the tree holds out.&quot;</p>
<footer>Robert A. Heinlein, <em>Methuselah&apos;s Children</em></footer>
</blockquote>
<p>You&apos;ve probably noticed in previous exercises, that when creating executable binaries of your Lisp programs to distribute or share, their size on your file system has been somewhat larger than you expected---over 80 MBs even for just a simple command-line application. If you were to deploy this same Lisp application with a commercial implementation of ANSI Common Lisp, however, you would get a much smaller application: for a simple command-line application, probably less than 1 MB. What gives, right? That&apos;s a pretty big discrepancy!</p>
<p>As it turns out, whenever you dump a Common Lisp environment to an executable binary, you&apos;re dumping <em>everything</em>. The entire Lisp language, every contrib package, the REPL, the debugger, all the packages you&apos;ve loaded in as dependencies, and your application itself. The commercial Lisps do this too---only they don&apos;t stop there, like the open-source implementations of Common Lisp---they then &quot;shake the tree&quot; of your Lisp application to prune all the unused symbols from the final executable. Your final executable binary then only contains a subset of Lisp needed to execute your program, and strips out everything else not needed for run-time.</p>
<p>There are pros and cons to both approaches. Many Lisp Hackers consider shipping the full Common Lisp environment with each instance of the application to be a feature---after all, you can embed a SWANK server into every app, and work with the live instance on the target platform, debugging and testing as it continues working. You can also provide a Lisp REPL to your users and let them customize everything in your program to their liking.</p>
<p>Commercial Lisps take a more traditional approach, and provide a clear separation between developers and users. So their binaries are stripped of everything that a user, in their view, should not have access to.</p>
<p>Whether or not you care about providing your users the full power of Common Lisp as a part of the application run-time, writing a tree-shaker is an interesting exercise, and may give you a deeper understanding of Lisp&apos;s implementation and execution on the machine level. To-date, the best example of a tree-shaker for SBCL was written several years ago by <a href="http://jsnell.iki.fi/blog/archive/2005-07-06.html" target="_blank">Juho Snellman</a>, but as SBCL has gone under considerable development since that time, it requires a fresh perspective---which is a perfect opportunity for learning!</p>
<p><strong>Revision Note:</strong> A More recent tree-shaker example is available from <a href="https://gist.github.com/burtonsamograd/f08f561264ff94391300" target="_blank">Burton Samograd</a>, with some relevant chat history from IRC included.</p>
<h3 id="exercise-2141">Exercise 2.14.1</h3>
<p><strong>Shaking Trees vs. Stripping Binaries</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2142">Exercise 2.14.2</h3>
<p><strong>Pruning Trees</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2143">Exercise 2.14.3</h3>
<p><strong>Unneccessary Run-Time Packages</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2144">Exercise 2.14.4</h3>
<p><strong>Full Garbage Collection</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2145">Exercise 2.14.5</h3>
<p><strong>Disabling the Debugger</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2146">Exercise 2.14.6</h3>
<p><strong>Type Safety</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2147">Exercise 2.14.7</h3>
<p><strong>A Basic Tree-Shaker</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2148">Exercise 2.14.8</h3>
<p><strong>Code-Walking</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-2149">Exercise 2.14.9</h3>
<p><strong>More Code-Walking</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-21410">Exercise 2.14.10</h3>
<p><strong>Even More Code-Walking</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-21411">Exercise 2.14.11</h3>
<p><strong>A Smart Tree-Shaker</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-21412">Exercise 2.14.12</h3>
<p><strong>NUKE-LISP-AND-DIE</strong></p>
<p>aka, Optimize, Collect, Shake, Save, Purify, Compress and Die</p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-21413">Exercise 2.14.13</h3>
<p><strong>Packaging the Tree-Shaker</strong></p>
<pre><code class="lang-lisp">
</code></pre>
<h3 id="exercise-21414">Exercise 2.14.14</h3>
<p><strong>Revisiting the 2D Game Engine</strong></p>
<pre><code class="lang-lisp">
</code></pre>
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