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diff --git a/src/content/chapter1_functions/lesson01_recursion/code.gleam b/src/content/chapter1_functions/lesson01_recursion/code.gleam
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+import gleam/io
+
+pub fn main() {
+  io.debug(factorial(5))
+  io.debug(factorial(7))
+}
+
+// A recursive functions that calculates factorial
+pub fn factorial(x: Int) -> Int {
+  case x {
+    // Base case
+    1 -> 1
+
+    // Recursive case
+    _ -> x * factorial(x - 1)
+  }
+}
diff --git a/src/content/chapter1_functions/lesson01_recursion/text.html b/src/content/chapter1_functions/lesson01_recursion/text.html
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+<p>
+  Gleam doesn't have loops, instead iteration is done through recursion, that is
+  through top-level functions calling themselves with different arguments.
+</p>
+<p>
+  A recursive function needs to have at least one <em>base case</em> and at
+  least one <em>recursive case</em>. A base case returns a value without calling
+  the function again. A recursive case calls the function again with different
+  inputs, looping again.
+</p>
+<p>
+  The Gleam standard library has functions for various common looping patterns,
+  some of which will be introduced in later lessons, however for more complex
+  loops manual recursion is often the clearest way to write it.
+</p>
+<p>
+  Recursion can seem daunting or unclear at first if you are more familiar with
+  languages that have special looping features, but stick with it! With time
+  it'll become just as familiar and comfortable as any other way of iterating.
+</p>
diff --git a/src/content/chapter1_functions/lesson02_tail_calls/code.gleam b/src/content/chapter1_functions/lesson02_tail_calls/code.gleam
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+import gleam/io
+
+pub fn main() {
+  io.debug(factorial(5))
+  io.debug(factorial(7))
+}
+
+pub fn factorial(x: Int) -> Int {
+  // The public function calls the private tail recursive function
+  factorial_loop(x, 1)
+}
+
+fn factorial_loop(x: Int, accumulator: Int) -> Int {
+  case x {
+    1 -> accumulator
+
+    // The last thing this function does is call itself
+    // In the previous lesson the last thing it did was multiple two ints
+    _ -> factorial_loop(x - 1, accumulator * x)
+  }
+}
diff --git a/src/content/chapter1_functions/lesson02_tail_calls/text.html b/src/content/chapter1_functions/lesson02_tail_calls/text.html
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+<p>
+  When a function is called a new stack frame is created in memory to store the
+  arguments and local variables of the function. If lots of these frames are
+  created during recursion then the program would use a large amount of memory,
+  or even crash the program if some limit is hit.
+</p>
+<p>
+  To avoid this problem Gleam supports <em>tail call optimisation</em>, which
+  allows the compiler to reuse the stack frame for the current function if a
+  function call is the last thing the function does, removing the memory cost.
+</p>
+
+<p>
+  Unoptimised recursive functions can often be rewritten into tail call
+  optimised functions by using an accumulator. An accumulator is a variable that
+  is passed along in addition to the data, similar to a mutable variable in a
+  language with <code>while</code> loops.
+</p>
+<p>
+  Accumulators should be hidden away from the users of your code, they are
+  internal implementation details. To do this write a public function that calls
+  a recursive private function with the initial accumulator value.
+</p>
diff --git a/src/content/chapter1_functions/lesson01_higher_order_functions/code.gleam b/src/content/chapter1_functions/lesson03_higher_order_functions/code.gleam
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diff --git a/src/content/chapter1_functions/lesson02_anonymous_functions/code.gleam b/src/content/chapter1_functions/lesson04_anonymous_functions/code.gleam
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diff --git a/src/content/chapter1_functions/lesson04_generic_functions/code.gleam b/src/content/chapter1_functions/lesson06_generic_functions/code.gleam
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diff --git a/src/content/chapter1_functions/lesson06_labelled_arguments/code.gleam b/src/content/chapter1_functions/lesson08_labelled_arguments/code.gleam
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diff --git a/src/content/chapter1_functions/lesson099_documentation_comments/code.gleam b/src/content/chapter1_functions/lesson09_documentation_comments/code.gleam
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diff --git a/src/content/chapter1_functions/lesson10_deprecations/code.gleam b/src/content/chapter1_functions/lesson10_deprecations/code.gleam
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+pub fn main() {
+  old_function()
+  new_function()
+}
+
+@deprecated("Use new_function instead")
+fn old_function() {
+  Nil
+}
+
+fn new_function() {
+  Nil
+}
diff --git a/src/content/chapter1_functions/lesson10_deprecations/text.html b/src/content/chapter1_functions/lesson10_deprecations/text.html
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+<p>
+  Functions and other definitions can be marked as deprecated using the
+  `@deprecated` attribute.
+</p>
+<p>
+  If a deprecated function is reference the compiler will emit a warning,
+  letting the programmer know they ought to update their code.
+</p>
+<p>
+  The deprecation atribute takes a message and this will be displayed to the
+  user in the warning. In the message explain to the user the new approach or
+  replacement function, or direct them on documentation on how to upgrade.
+</p>
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