1 files changed, 87 insertions, 0 deletions
diff --git a/std/default/options.pk b/std/default/options.pk
new file mode 100644
index 0000000..f1bcac4
--- /dev/null
+++ b/std/default/options.pk
@@ -0,0 +1,87 @@
+## std/options
+## This module is imported by default.
+
+import std/format
+
+pub type Option[T] = union
+  Some: T
+  None
+
+pub func is_some[T](self: Option[T]): bool =
+  self of Some(_)
+pub func is_none[T](self: Option[T]): bool =
+  not self.is_some
+
+## Converts an Option[T] to a Result[T, E] given a user-provided error.
+pub func err[T, E](self: Option[T], error: E): Result[T, E] =
+  if self of Some(x):
+    Okay(x)
+  else:
+    Error(error)
+
+## Applies a function to T, if it exists.
+pub func map[T, U](self: Option[T], proc: T -> U): Option[U] =
+  if self of Some(x):
+    Some(x.proc)
+  else:
+    None
+## Converts T to a None, if proc returns false and it exists.
+pub func filter[T](self: Option[T], proc: T -> bool): Option[T] =
+  if self of Some(x) and proc(x):
+    Some(x)
+  else:
+    None
+
+## Applies a function to T, if it exists. Equivalent to .map(func).flatten.
+pub func flatmap[T, U](self: Option[T], proc: T -> Option[U]): Option[U] =
+  if self of Some(x):
+    x.proc
+  else:
+    None
+## Converts from Option[Option[T]] to Option[T].
+pub func flatten[T](self: Option[Option[T]]): Option[T] = # todo: better name?
+  match self
+  of Some(Some(x)):
+    Some(x)
+  of _:
+    None
+
+## Returns the inner value or a default.
+pub func or[T](self: Option[T], default: T): T =
+  if self of Some(x): x
+  else: default
+## Directly accesses the inner value. Throws an exception if None.
+pub yeet func get[T](self: Option[T]): T =
+  if self of Some(x): x
+  else: raise Exception # todo: syntax??
+
+# todo: direct access, alias to get
+macro `!`[T](self: Option[T]): T
+# todo: indirect access, ??? do we propagate? is this useful? probably not
+macro `?`[T](self: Option[T]): T
+# todo: field access? useful? assignment?
+macro `.?`[T](self: Option[T])
+
+## Overloads the == operation for use on Options.
+pub func `==`[T](a, b: Option[T]): bool =
+  match (a, b)
+  of (Some(x), Some(y)):
+    x == y
+  of _:
+    false
+
+## Overloads the str() function for use on Options.
+pub func str[T](self: Option[T]): str =
+  if self of Some(x):
+    fmt("some({})", x.str)
+  else:
+    "none"
+
+examples:
+  let x = Some(42)
+  if x of Some(y):
+    assert x! == y
+
+# references:
+# https://nim-lang.github.io/Nim/options.html
+# https://doc.rust-lang.org/std/option/enum.Option.html