Add a Symbol abstraction

Technologicat · Technologicat · commit 25850bb5aa10 · 2020-03-04T23:38:38.000+02:00
diff --git a/unpythonic/__init__.py b/unpythonic/__init__.py
@@ -36,6 +36,7 @@
 from .seq import *
 from .singleton import *
 from .slicing import *
+from .symbol import *
 from .tco import *
 
 # HACK: break dependency loop
diff --git a/unpythonic/symbol.py b/unpythonic/symbol.py
@@ -0,0 +1,23 @@
+# -*- coding: utf-8; -*-
+"""A lispy symbol type for Python."""
+
+__all__ = ["Symbol"]
+
+_symbols = {}
+
+class Symbol:
+    def __new__(cls, name):  # This covers unpickling, too.
+        if name not in _symbols:
+            _symbols[name] = super().__new__(cls)
+        return _symbols[name]
+    def __init__(self, name):
+        self.name = name
+
+    # pickle support
+    def __getnewargs__(self):
+        return (self.name,)
+
+    def __str__(self):
+        return self.name
+    def __repr__(self):
+        return 'Symbol("{}")'.format(self.name)
diff --git a/unpythonic/test/test_symbol.py b/unpythonic/test/test_symbol.py
@@ -0,0 +1,29 @@
+# -*- coding: utf-8; -*-
+
+import pickle
+
+from ..symbol import Symbol as S
+
+def test():
+    # Basic idea: lightweight, human-readable, process-wide unique marker,
+    # that can be quickly compared by object identity.
+    assert S("foo") is S("foo")
+
+    # Works even if pickled.
+    sym = S("foo")
+    s = pickle.dumps(sym)
+    o = pickle.loads(s)
+    assert o is sym
+    assert o is S("foo")
+
+    # str() returns the human-readable name as a string.
+    assert str(S("foo")) == "foo"
+
+    # Has nothing to do with string interning.
+    assert "λ" * 80 is not "λ" * 80
+    assert S("λ" * 80) is S("λ" * 80)
+
+    print("All tests PASSED")
+
+if __name__ == '__main__':
+    test()
