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fix and test expressions of the form BoxExpression[[...]] #561

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fix and test expressions of the form BoxExpression[[...]]
mmatera Sep 20, 2022
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mmatera Sep 20, 2022
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mmatera Oct 22, 2022
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fix CHANGES
mmatera Oct 22, 2022
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Merge branch 'master' into box_part
mmatera May 24, 2023
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3 changes: 2 additions & 1 deletion CHANGES.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,8 @@ Internals
Bugs
++++

# ``0`` with a given precision (like in ```0`3```) is now parsed as ``0``, an integer number.
#. ``0`` with a given precision (like in ```0`3```) is now parsed as ``0``, an integer number.
#. `RowBox` now have an `elements` attribute, in a way that expressions like `Part[RowBox[{"a"}],1]` does not raises an unhandled exception.


Enhancements
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11 changes: 9 additions & 2 deletions mathics/builtin/box/layout.py
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Expand Up @@ -305,6 +305,13 @@ def apply_list(self, boxes, evaluation):
result = RowBox(*items)
return result

@property
def elements(self):
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It feels like something in the code or the API is wrong here.

I get nervous about "properties" doing possibly unbounded calculations such as self.to_expressions().

If I understand correctly, the caller somehow knows this is a compound Expression/Element and assumes that therefore it has an .element attribute which is of type Expression?

It feels like what should be happening that the caller should be asking instead for a conversion, that is, should be calling to_expression().elements

I need to think about this more.

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It feels like something in the code or the API is wrong here.

Probably it is, but I tried to build over the existing API. At least, this is "localized" in this class.

I get nervous about "properties" doing possibly unbounded calculations such as self.to_expressions().

If I understand correctly, the caller somehow knows this is a compound Expression/Element and assumes that therefore it has an .element attribute which is of type Expression?

The problem is that Part assumes that an Expression has a property elements. This just provides the property by creating an Expression. A different possibility would be to implement a different rule for working with RowBoxes. I thought this change was simpler, but maybe there is a better approach.

It feels like what should be happening that the caller should be asking instead for a conversion, that is, should be calling to_expression().elements

I need to think about this more.

Sure.

return self.to_expression().elements

def get_head(self):
return SymbolRowBox

def init(self, *items, **kwargs):
# TODO: check that each element is an string or a BoxElementMixin
self.box_options = {}
Expand Down Expand Up @@ -352,8 +359,8 @@ def to_expression(self) -> Expression:
for item in self.items
)

self._elements = Expression(SymbolRowBox, ListExpression(*items))
return self._elements
self._elements = ListExpression(*items)
return Expression(SymbolRowBox, self._elements)


class ShowStringCharacters(Builtin):
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34 changes: 34 additions & 0 deletions test/builtin/test_makeboxes.py
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Expand Up @@ -12,6 +12,40 @@
else:
skip_or_fail = pytest.mark.skip


@pytest.mark.parametrize(
("str_expr", "str_expected", "fail_msg", "msgs"),
[
('rb=RowBox[{"a", "b"}]; rb[[1]]', "{a, b}", None, []),
("rb[[0]]", "RowBox", None, []),
(
"rb[[2]]",
"RowBox[{a, b}][[2]]",
None,
["Part 2 of RowBox[{a, b}] does not exist."],
),
('fb=FractionBox["1", "2"]; fb[[0]]', "FractionBox", None, []),
("fb[[1]]", "1", None, []),
('sb=StyleBox["string", "Section"]; sb[[0]]', "StyleBox", None, []),
("sb[[1]]", "string", None, []),
# FIXME: <<RowBox object does not have the attribute "restructure">>
# ('rb[[All, 1]]', "{a, b}", "\"a\"", []),
# ('fb[[All]][[1]]','1', None, []),
# ('sb[[All]][[1]]','string', None, []),
],
)
def test_part_boxes(str_expr, str_expected, fail_msg, msgs):
check_evaluation(
str_expr,
str_expected,
to_string_expr=True,
to_string_expected=True,
hold_expected=True,
failure_message=fail_msg,
expected_messages=msgs,
)


# 15 tests
@pytest.mark.parametrize(
("str_expr", "str_expected", "msg"),
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