More stdlib

2 files changed, 64 insertions, 0 deletions

diff --git a/src/content/chapter4_standard_library/lesson02_result_module/code.gleam b/src/content/chapter4_standard_library/lesson02_result_module/code.gleam
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+import gleam/io
+import gleam/int
+import gleam/result
+
+pub fn main() {
+  io.println("=== map ===")
+  io.debug(result.map(Ok(1), fn(x) { x * 2 }))
+  io.debug(result.map(Error(1), fn(x) { x * 2 }))
+
+  io.println("=== try ===")
+  io.debug(result.try(Ok("1"), int.parse))
+  io.debug(result.try(Ok("no"), int.parse))
+  io.debug(result.try(Error(Nil), int.parse))
+
+  io.println("=== unwrap ===")
+  io.debug(result.unwrap(Ok("1234"), "default"))
+  io.debug(result.unwrap(Error(Nil), "default"))
+
+  io.println("=== pipeline ===")
+  int.parse("-1234")
+  |> result.map(int.absolute_value)
+  |> result.try(int.remainder(_, 42))
+  |> io.debug
+}
diff --git a/src/content/chapter4_standard_library/lesson02_result_module/text.html b/src/content/chapter4_standard_library/lesson02_result_module/text.html
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+<p>
+  The
+  <a href="https://hexdocs.pm/gleam_stdlib/gleam/result.html"
+    ><code>gleam/result</code></a
+  >
+  standard library module contains functions for working with results. Gleam
+  programs will make heavy use of this module to avoid excessive nested case
+  expressions when calling multiple functions that can fail.
+</p>
+
+<p>
+  <a href="https://hexdocs.pm/gleam_stdlib/gleam/result.html#map"
+    ><code>map</code></a
+  >
+  updates a value held within the Ok of a result by calling a given function on
+  it. If the result is an error then the function is not called.
+</p>
+
+<p>
+  <a href="https://hexdocs.pm/gleam_stdlib/gleam/result.html#try"
+    ><code>try</code></a
+  >
+  runs a result returning function on the value held within an Ok of a result.
+  If the result is an error then the function is not called. This is useful for
+  chaining together multiple function calls that can fail, one after the other,
+  stopping at the first error.
+</p>
+
+<p>
+  <a href="https://hexdocs.pm/gleam_stdlib/gleam/result.html#unwrap"
+    ><code>unwrap</code></a
+  >
+  extracts the success value from a result, or returning a default value if the
+  result is an error.
+</p>
+
+<p>
+  Result functions are often used with pipelines to chain together multiple
+  calls to result returning functions.
+</p>