From 6a53724432d00a0e3a440bb71f8ed7c0bbc9233c Mon Sep 17 00:00:00 2001
From: salt-die <53280662+salt-die@users.noreply.github.com>
Date: Sun, 26 Nov 2023 14:00:24 -0600
Subject: [PATCH] Added `x`.

---
 src/mind_the_gaps/__init__.py |  3 ++-
 src/mind_the_gaps/var.py      | 44 +++++++++++++++++++++++++++++++++++
 tests/test_x.py               | 15 ++++++++++++
 3 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 src/mind_the_gaps/var.py
 create mode 100644 tests/test_x.py

diff --git a/src/mind_the_gaps/__init__.py b/src/mind_the_gaps/__init__.py
index 9c10ece..bd6cbaf 100644
--- a/src/mind_the_gaps/__init__.py
+++ b/src/mind_the_gaps/__init__.py
@@ -1,5 +1,6 @@
 """A library for unions, intersections, subtractions, and xors of intervals (gaps)."""
 from .gaps import Endpoint, Gaps, NegativeInfinity, PositiveInfinity
+from .var import x
 
-__all__ = ["Gaps", "PositiveInfinity", "NegativeInfinity", "Endpoint"]
+__all__ = ["Gaps", "PositiveInfinity", "NegativeInfinity", "Endpoint", "x"]
 __version__ = "0.2.0"
diff --git a/src/mind_the_gaps/var.py b/src/mind_the_gaps/var.py
new file mode 100644
index 0000000..7ca8199
--- /dev/null
+++ b/src/mind_the_gaps/var.py
@@ -0,0 +1,44 @@
+from dataclasses import dataclass
+
+from .gaps import Endpoint, SupportsLessThan
+
+__all__ = ["x"]
+
+
+@dataclass
+class _Var[T: SupportsLessThan]:
+    name: str
+
+    def __str__(self):
+        return self.name
+
+    def __gt__(self, value: T) -> Endpoint:
+        return Endpoint(value, "(")
+
+    def __ge__(self, value: T) -> Endpoint:
+        return Endpoint(value, "[")
+
+    def __lt__(self, value: T) -> Endpoint:
+        return Endpoint(value, ")")
+
+    def __le__(self, value: T) -> Endpoint:
+        return Endpoint(value, "]")
+
+
+x = _Var("x")
+"""
+A very convenient constructor for `Endpoints`.
+
+It's best to start with an example::
+    >>> from mind_the_gaps import x
+    >>> 0 <= x
+    Endpoint(value=0, boundary='[')
+    >>> x < 1
+    Endpoint(value=1, boundary=')')
+    >>> print(Gaps([0 <= x, x < 1]))
+    {[0, 1)}
+
+Values compared with `x` will return an endpoint. The type of comparison determines
+the boundary of the endpoint. `>` is left-open, `>=` is left-closed, `<` is right-open,
+and `<=` is right-closed.
+"""
diff --git a/tests/test_x.py b/tests/test_x.py
new file mode 100644
index 0000000..26db71d
--- /dev/null
+++ b/tests/test_x.py
@@ -0,0 +1,15 @@
+from mind_the_gaps import Endpoint, Gaps, x
+
+
+def test_x_closed():
+    assert Gaps([0 <= x, x <= 1, 2 <= x, x <= 3]) == Gaps([0, 1, 2, 3])
+
+
+def test_x_open():
+    assert Gaps([0 < x, x < 1, 2 < x, x < 3]) == Gaps(
+        [Endpoint(0, "("), Endpoint(1, ")"), Endpoint(2, "("), Endpoint(3, ")")]
+    )
+
+
+def test_x_singleton():
+    assert Gaps([0 <= x, x <= 0]) == Gaps([0, 0])