adding evaluate_without_side_effects for helping compile expressions.

mathics/builtin/assignments/assignment.py

@@ -134,7 +134,7 @@ class Set(InfixOperator):
         "setraw": "Cannot assign to raw object `1`.",
         "shape": "Lists `1` and `2` are not the same shape.",
     }
-
+    has_side_effects = True
     summary_text = "assign a value"
 
     def eval(self, lhs, rhs, evaluation):
@@ -258,7 +258,7 @@ class TagSet(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED | A_SEQUENCE_HOLD
-
+    has_side_effects = True
     messages = {
         "tagnfd": "Tag `1` not found or too deep for an assigned rule.",
     }
@@ -353,6 +353,7 @@ class UpSet(InfixOperator):
     """
 
     attributes = A_HOLD_FIRST | A_PROTECTED | A_SEQUENCE_HOLD
+    has_side_effects = True
     grouping = "Right"
 
     summary_text = (

mathics/builtin/attributes.py

@@ -126,6 +126,7 @@ class ClearAttributes(Builtin):
     """
 
     attributes = A_HOLD_FIRST | A_PROTECTED
+    has_side_effects = True
     summary_text = "clear the attributes of a symbol"
 
     def eval(self, symbols, attributes, evaluation):
@@ -526,6 +527,7 @@ class Protect(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
+    has_side_effects = True
     summary_text = "protect a symbol against redefinitions"
 
     def eval(self, symbols, evaluation):
@@ -696,7 +698,7 @@ class SetAttributes(Builtin):
     """
 
     attributes = A_HOLD_FIRST | A_PROTECTED
-
+    has_side_effects = True
     messages = {
         "unknownattr": f"`1` should be one of {', '.join(attribute_string_to_number.keys())}"
     }
@@ -752,6 +754,7 @@ class Unprotect(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
+    has_side_effects = True
     summary_text = "remove protection against redefinitions"
 
     def eval(self, symbols, evaluation):

mathics/builtin/procedural.py

@@ -219,7 +219,7 @@ class CompoundExpression(InfixOperator):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED | A_READ_PROTECTED
-
+    has_side_effects = True
     summary_text = "execute expressions in sequence"
 
     def eval(self, expr, evaluation):
@@ -346,6 +346,7 @@ class For(Builtin):
     """
 
     attributes = A_HOLD_REST | A_PROTECTED
+    has_side_effects = True
     rules = {
         "For[start_, test_, incr_]": "For[start, test, incr, Null]",
     }
@@ -486,6 +487,7 @@ class Interrupt(Builtin):
      | a
      = $Aborted
     """
+    has_side_effects = True
 
     # Set checking that the no arguments are allowed.
     # eval_error = Builtin.generic_argument_error
@@ -511,6 +513,7 @@ class Pause(Builtin):
     >> Pause[0.5]
     """
 
+    has_side_effects = True
     messages = {
         "numnm": (
             "Non-negative machine-sized number expected at " "position 1 in `1`."
@@ -563,7 +566,7 @@ class Return(Builtin):
     rules = {
         "Return[]": "Return[Null]",
     }
-
+    has_side_effects = True
     summary_text = "return from a function"
 
     def eval(self, expr, evaluation: Evaluation):  # pylint: disable=unused-argument
@@ -604,7 +607,7 @@ class Switch(Builtin):
 
     summary_text = "switch based on a value, with patterns allowed"
     attributes = A_HOLD_REST | A_PROTECTED
-
+    has_side_effects = True
     messages = {
         "argct": (
             "Switch called with `2` arguments. "
@@ -659,7 +662,7 @@ class Throw(Builtin):
     # Set checking that the number of arguments required is one or two. WMA uses 1..3.
     eval_error = Builtin.generic_argument_error
     expected_args = (1, 2)
-
+    has_side_effects = True
     messages = {
         "nocatch": "Uncaught `1` returned to top level.",
     }
@@ -714,6 +717,7 @@ class Which(SympyFunction):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
+    has_side_effects = True
     summary_text = "test which of a sequence of conditions are true"
 
     def eval(self, items, evaluation):
@@ -773,7 +777,7 @@ class While(Builtin):
     # Set checking that the number of arguments required is one.
     eval_error = Builtin.generic_argument_error
     expected_args = (1, 2)
-
+    has_side_effects = True
     rules = {
         "While[test_]": "While[test, Null]",
     }

mathics/builtin/scoping.py

@@ -99,6 +99,7 @@ class Begin(Builtin):
     ##  = Global`test`
     """
 
+    has_side_effects = True
     rules = {
         "Begin[context_String]": """
              Unprotect[System`Private`$ContextStack];
@@ -128,7 +129,7 @@ class BeginPackage(Builtin):
     ## >> BeginPackage["test`"]
     ##  = test`
     """
-
+    has_side_effects = True
     messages = {"unimpl": "The second argument to BeginPackage is not yet implemented."}
 
     rules = {
@@ -187,7 +188,7 @@ class Block(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
-
+    has_side_effects = True
     messages = {
         "lvsym": (
             "Local variable specification contains `1`, "
@@ -351,6 +352,7 @@ class End(Builtin):
     </dl>
     """
 
+    has_side_effects = True
     messages = {
         "noctx": "No previous context defined.",
     }
@@ -385,7 +387,7 @@ class EndPackage(Builtin):
     After 'EndPackage', the values of '\$Context' and '\$ContextPath' at the \
     time of the 'BeginPackage' call are restored, with the new package\'s context prepended to '\$ContextPath'.
     """
-
+    has_side_effects = True
     messages = {
         "noctx": "No previous context defined.",
     }
@@ -450,7 +452,7 @@ class Module(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
-
+    has_side_effects = True
     messages = {
         "lvsym": (
             "Local variable specification contains `1`, "
@@ -710,7 +712,7 @@ class With(Builtin):
     """
 
     attributes = A_HOLD_ALL | A_PROTECTED
-
+    has_side_effects = True
     messages = {
         "lvsym": (
             "Local variable specification contains `1`, "

mathics/core/builtin.py

@@ -207,6 +207,11 @@ def eval_with_options(x, evaluation: Evaluation, options: dict):
     expected_args: Union[int, Tuple[int, int], range] = -1
 
     formats: Dict[str, Any] = {}
+
+    # If the symbol include rules involving loops,
+    # setting values, or creating/changing contexts.
+    has_side_effects: bool = False
+
     messages: Dict[str, Any] = {}
     name: Optional[str] = None
     options: Dict[str, Any] = {}
@@ -434,6 +439,13 @@ def contextify_form_name(f):
         else:
             definitions.builtin[name] = definition
 
+        # If the definition has side effects, store it in a
+        # dictionary.
+        if self.has_side_effects:
+            from mathics.core.definitions import SIDE_EFFECT_BUILTINS
+
+            SIDE_EFFECT_BUILTINS[name] = definition
+
         makeboxes_def = definitions.builtin["System`MakeBoxes"]
         for rule in box_rules:
             makeboxes_def.add_rule(rule)
@@ -1024,6 +1036,7 @@ def get_name(cls, short=False) -> str:
 class IterationFunction(Builtin, ABC):
     attributes = A_HOLD_ALL | A_PROTECTED
     allow_loopcontrol = False
+    has_side_effects = True
     throw_iterb = True
 
     def get_result(self, elements, is_uniform=False) -> Expression:

mathics/core/convert/function.py

@@ -2,6 +2,8 @@
 
 from typing import Callable, Optional, Tuple
 
+from mathics.core.definitions import SIDE_EFFECT_BUILTINS, Definition
+from mathics.core.element import BaseElement
 from mathics.core.evaluation import Evaluation
 from mathics.core.expression import Expression, from_python
 from mathics.core.symbols import Symbol, SymbolFalse, SymbolTrue
@@ -44,6 +46,32 @@ def __init__(self, var):
         self.var = var
 
 
+def evaluate_without_side_effects(
+    expr: BaseElement, evaluation: Evaluation
+) -> BaseElement:
+    """
+    Evaluate an expression leaving unevaluated subexpressions
+    related with side-effects (assignments, loops).
+    """
+    definitions = evaluation.definitions
+    # Temporarily remove the builtin definitions
+    # of symbols with side effects
+    for name, defin in SIDE_EFFECT_BUILTINS.items():
+        # Change the definition by a temporal definition setting
+        # just the name and the attributes.
+        definitions.builtin[name] = Definition(
+            name, attributes=defin.attributes, builtin=defin.builtin
+        )
+        definitions.clear_cache(name)
+    try:
+        result = expr.evaluate(evaluation)
+    finally:
+        # Restore the definitions
+        for name, defin in SIDE_EFFECT_BUILTINS.items():
+            definitions.builtin[name] = defin
+    return result
+
+
 def expression_to_callable(
     expr: Expression,
     args: Optional[list] = None,
@@ -56,6 +84,7 @@ def expression_to_callable(
     args: a list of CompileArg elements
     evaluation: an Evaluation object used if the llvm compilation fails
     """
+    expr = evaluate_without_side_effects(expr, evaluation)
     try:
         cfunc = _compile(expr, args) if (use_llvm and args is not None) else None
     except CompileError:

mathics/core/definitions.py

@@ -121,6 +121,12 @@ def __repr__(self) -> str:
         return repr_str
 
 
+# Dictionary of builtin definitions involving side effects
+# like setting values, changing contexts or running loops:
+
+SIDE_EFFECT_BUILTINS: Dict[str, Definition] = {}
+
+
 class Definitions:
     """The state of one instance of the Mathics3 interpreter is stored in this object.
 

mathics/eval/drawing/plot_compile.py

@@ -18,6 +18,7 @@
 import scipy
 import sympy
 
+from mathics.core.convert.function import evaluate_without_side_effects
 from mathics.core.convert.sympy import SympyExpression
 from mathics.core.symbols import strip_context
 from mathics.core.util import print_expression_tree, print_sympy_tree
@@ -54,7 +55,7 @@ def plot_compile(evaluation, expr, names, debug=0):
     # because some functions are not themselves sympy-enabled
     # if they always get rewritten to one that is.
     try:
-        new_expr = expr.evaluate(evaluation)
+        new_expr = eval_without_side_effects(expr, evaluation)
         if new_expr:
             expr = new_expr
     except Exception: