Can do logical negation.

interpreter.py

@@ -845,6 +845,8 @@ class Interpreter():
             return self.evaluate_andstatement(cur)
         elif isinstance(cur, nodes.OrStatement):
             return self.evaluate_orstatement(cur)
+        elif isinstance(cur, nodes.NotStatement):
+            return self.evaluate_notstatement(cur)
         else:
             raise InvalidCode("Unknown statement.")
 
@@ -1263,6 +1265,14 @@ class Interpreter():
         if not isinstance(r, bool):
             raise InterpreterException('Second argument to "or" is not a boolean.')
         return r
+    
+    def evaluate_notstatement(self, cur):
+        v = self.evaluate_statement(cur.val)
+        if isinstance(v, nodes.BoolStatement):
+            v = v.get_value()
+        if not isinstance(v, bool):
+            raise InterpreterException('First argument to "or" is not a boolean.')
+        return not v
 
     def evaluate_arraystatement(self, cur):
         (arguments, kwargs) = self.reduce_arguments(cur.get_args())

mparser.py

@@ -71,6 +71,7 @@ precedence = (
 ('nonassoc', 'EQUALS', 'NEQUALS'),
 ('left', 'OR'),
 ('left', 'AND'),
+('right', 'NOT'),
 ('nonassoc', 'COLON'),
 ('left', 'DOT'),
 )
@@ -200,6 +201,10 @@ def p_statement_or(t):
     'statement : statement OR statement'
     t[0] = nodes.OrStatement(t[1], t[3])
 
+def p_statement_not(t):
+    'statement : NOT statement'
+    t[0] = nodes.NotStatement(t[2])
+
 def p_empty_else(t):
     'elseblock : '
     return None

nodes.py

@@ -94,6 +94,11 @@ class OrStatement(Statement):
         self.left = left
         self.right = right
 
+class NotStatement(Statement):
+    def __init__(self, val):
+        Statement.__init__(self, val.lineno)
+        self.val = val
+
 class IfStatement(Statement):
     def __init__(self, clause, trueblock, falseblock, lineno):
         Statement.__init__(self, lineno)

test cases/common/40 logic ops/meson.build

@@ -62,3 +62,16 @@ if t or true
 else
   error('Not ok.')
 endif
+
+if not true
+  error('Negation failed.')
+else
+  message('Ok.')
+endif
+
+if not f
+  message('Ok.')
+else
+  error('Negation failed.')
+endif
+