Enable one optimization

Due to the fact that the nodes are different classes, this required some refactor.

relational/optimizations.py

@@ -30,6 +30,7 @@
 
 from io import StringIO
 from tokenize import generate_tokens
+from typing import Tuple
 
 
 from relational import parser
@@ -98,36 +99,7 @@ def replace_node(replace, replacement):
         replace.left = replacement.left
 
 
-def recoursive_scan(function, node, rels=None):
-    '''Does a recoursive optimization on the tree.
-
-    This function will recoursively execute the function given
-    as "function" parameter starting from node to all the tree.
-    if rels is provided it will be passed as argument to the function.
-    Otherwise the function will be called just on the node.
-
-    Result value: function is supposed to return the amount of changes
-    it has performed on the tree.
-    The various result will be added up and this final value will be the
-    returned value.'''
-    changes = 0
-    # recoursive scan
-    if node.kind == parser.UNARY:
-        if rels != None:
-            changes += function(node.child, rels)
-        else:
-            changes += function(node.child)
-    elif node.kind == parser.BINARY:
-        if rels != None:
-            changes += function(node.right, rels)
-            changes += function(node.left, rels)
-        else:
-            changes += function(node.right)
-            changes += function(node.left)
-    return changes
-
-
-def duplicated_select(n: parser.Node) -> int:
+def duplicated_select(n: parser.Node) -> Tuple[parser.Node, int]:
     '''This function locates and deletes things like
     σ a ( σ a(C)) and the ones like σ a ( σ b(C))
     replacing the 1st one with a single select and
@@ -135,19 +107,22 @@ def duplicated_select(n: parser.Node) -> int:
     in and
     '''
     changes = 0
-    if n.name == SELECTION and n.child.name == SELECTION:
+    while n.name == SELECTION and n.child.name == SELECTION:
+        changes += 1
+        prop = n.prop
+
         if n.prop != n.child.prop:  # Nested but different, joining them
-            n.prop = n.prop + " and " + n.child.prop
+            prop = n.prop + " and " + n.child.prop
 
             # This adds parenthesis if they are needed
             if n.child.prop.startswith('(') or n.prop.startswith('('):
-                n.prop = '(%s)' % n.prop
-
-        n.child = n.child.child
-        changes = 1
-        changes += duplicated_select(n)
-
-    return changes + recoursive_scan(duplicated_select, n)
+                prop = '(%s)' % prop
+        n = parser.Unary(
+            SELECTION,
+            prop,
+            n.child.child,
+        )
+    return n, changes
 
 
 def futile_union_intersection_subtraction(n: parser.Node) -> int:
@@ -706,10 +681,10 @@ def useless_projection(n, rels) -> int:
         changes = 1
         replace_node(n, n.child)
 
-    return changes + recoursive_scan(useless_projection, n, rels)
+    return changes + recursive_scan(useless_projection, n, rels)
 
 general_optimizations = [
-    #duplicated_select,
+    duplicated_select,
     #down_to_unions_subtractions_intersections,
     #duplicated_projection,
     #selection_inside_projection,

relational/optimizer.py

@@ -1,5 +1,5 @@
 # Relational
-# Copyright (C) 2008-2016  Salvo "LtWorf" Tomaselli
+# Copyright (C) 2008-2020  Salvo "LtWorf" Tomaselli
 #
 # Relational is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -22,10 +22,10 @@
 # relational query, or it can be a parse tree for a relational expression (ie: class parser.node).
 # The functions will always return a string with the optimized query, but if a parse tree was provided,
 # the parse tree itself will be modified accordingly.
-from typing import Union, Optional, Dict, Any
+from typing import Union, Optional, Dict, Any, Tuple
 
 from relational import optimizations
-from relational.parser import Node, RELATION, UNARY, BINARY, op_functions, tokenize, tree
+from relational.parser import Node, Variable, Unary, Binary, op_functions, tokenize, tree
 from relational import querysplit
 from relational.maintenance import UserInterface
 
@@ -88,10 +88,10 @@ def optimize_all(expression: Union[str, Node], rels: ContextDict, specific: bool
                 total += res
         if general:
             for i in optimizations.general_optimizations:
-                res = i(n)  # Performs the optimization
-                if res != 0 and dbg:
+                n, c = recursive_scan(i, n, None)
+                if c != 0 and dbg:
                     debug.append(str(n))
-                total += res
+                total += c
     if tostr:
         return str(n)
     else:
@@ -117,3 +117,35 @@ def general_optimize(expression):
 
     Return value: this will return an optimized version of the expression'''
     return optimize_all(expression, None, specific=False, general=True)
+
+
+def recursive_scan(function, node, rels) -> Tuple[Node, int]:
+    '''Does a recursive optimization on the tree.
+
+    This function will recursively execute the function given
+    as "function" parameter starting from node to all the tree.
+    if rels is provided it will be passed as argument to the function.
+    Otherwise the function will be called just on the node.
+
+    Result value: function is supposed to return the amount of changes
+    it has performed on the tree.
+    The various result will be added up and this final value will be the
+    returned value.'''
+
+    args = []
+    if rels:
+        args.append(rels)
+
+    changes = 0
+    node, c = function(node, *args)
+    changes += c
+
+    if isinstance(node, Unary):
+        node.child, c = recursive_scan(function, node.child, rels)
+        changes += c
+    elif isinstance(node, Binary):
+        node.left, c = recursive_scan(function, node.left, rels)
+        changes += c
+        node.right, c = recursive_scan(function, node.right, rels)
+        changes += c
+    return node, changes