fix test for SetDelayed. Move special case for Set with LHS a list away from the conditional.

Author: mmatera

mathics/builtin/assignments/assignment.py

@@ -146,21 +146,28 @@ class SetDelayed(Set):
      = -2 / 3
     We can use conditional delayed assignments to define \
     symbols with values conditioned to the context. For example,
-    >> a/; b>0:= 3
+    >> ClearAll[a,b]; a/; b>0:= 3
     Set $a$ to have a value of $3$ if certain variable $b$ is positive.\
     So, if this variable is not set, $a$ stays unevaluated:
     >> a
      = a
     If now we assign a positive value to $b$, then $a$ is evaluated:
     >> b=2; a
      =  3
-    Notice however that if we assign an unconditional value to $a$, \
-    this overrides the condition:
-    >> a:=0; a/; b>1:= 3
-    >> a
-     = 0
     """
 
+    #  I WMA, if we assign a value without a condition on the LHS,
+    # conditional values are never reached. So,
+    #
+    # Notice however that if we assign an unconditional value to $a$, \
+    # this overrides the condition:
+    # >> a:=0; a/; b>1:= 3
+    # >> a
+    # = 0
+    #
+    # In Mathics, this last line would return 3
+    # """
+
     operator = ":="
     attributes = A_HOLD_ALL | A_PROTECTED | A_SEQUENCE_HOLD
 

mathics/builtin/assignments/internals.py

@@ -612,6 +612,19 @@ def process_assign_format(self, lhs, rhs, evaluation, tags, upset):
     return count > 0
 
 
+def process_assign_list(self, lhs, rhs, evaluation, tags, upset):
+    if not (
+        rhs.get_head_name() == "System`List" and len(lhs.elements) == len(rhs.elements)
+    ):  # nopep8
+        evaluation.message(self.get_name(), "shape", lhs, rhs)
+        return False
+    result = True
+    for left, right in zip(lhs.elements, rhs.elements):
+        if not self.assign(left, right, evaluation):
+            result = False
+    return result
+
+
 def process_assign_makeboxes(self, lhs, rhs, evaluation, tags, upset):
     # FIXME: the below is a big hack.
     # Currently MakeBoxes boxing is implemented as a bunch of rules.
@@ -768,6 +781,7 @@ class _SetOperator:
         "System`DefaultValues": process_assign_definition_values,
         "System`DownValues": process_assign_definition_values,
         "System`Format": process_assign_format,
+        "System`List": process_assign_list,
         "System`MakeBoxes": process_assign_makeboxes,
         "System`MessageName": process_assign_messagename,
         "System`Messages": process_assign_definition_values,
@@ -800,11 +814,10 @@ def assign_elementary(self, lhs, rhs, evaluation, tags=None, upset=False):
     def assign(self, lhs, rhs, evaluation):
         # lhs._format_cache = None
         defs = evaluation.definitions
-        if lhs.get_head_name() == "System`List":
+        if False and lhs.get_head_name() == "System`List":
             if not (rhs.get_head_name() == "System`List") or len(lhs.elements) != len(
                 rhs.elements
             ):  # nopep8
-
                 evaluation.message(self.get_name(), "shape", lhs, rhs)
                 return False
             else: