borman · October 26, 2014 21:28 · Oct 26, 2014
diff --git a/sourcecodegen_wtf.py b/sourcecodegen_wtf.py
@@ -0,0 +1,29 @@
+def unary(symbol, priority):
+    # XXX: BRAIN DAMAGE HAZARD AHEAD
+    # Consider prioritize's argument: what's it for?
+    # Isn't it expected to be a number?
+    # How dare it work and work correctly?
+    # Turns out, Python mixed-type comparison semantics are exploited in an
+    # awkward way. Python specifies that when no other rules apply, e.g. no
+    # overridden comparison magic-methods on any side, it falls back to
+    # comparing both sides' type names.
+    # One could grep CPython sources for `default_3way_compare' function that
+    # defines comparison logic. It also turns out that when comparing a number
+    # vs. a non-number, number has an _empty_ type name.
+    # As one may observe, '' is less than 'function'
+    # Thus, for all int values ``v`` holds:
+    # - v < prioritize
+    # - prioritize > v
+    # - prioritize == prioritize
+    # So, ``prioritize`` is effectively is used as an `infinity' constant.
+    @prioritize(prioritize)
+    def visit(self, node):
+        yield symbol
+        child = self.visit(node.expr)
+        if child.priority < priority:
+            yield '('
+            yield child
+            yield ')'
+        else:
+            yield child
+    return visit