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feat: math expression language implementation

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Domenico Testa
2026-01-29 22:12:40 +01:00
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commit ad9c3af0ac
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import pytest
from plotter.parser import (
lex,
parse,
Atom,
Token,
TokenType,
InfixExpression,
FunctionExpression,
)
@pytest.mark.parametrize(
"expression, expected",
[
("+", [Token(type=TokenType.OPERATOR, value="+")]),
("x", [Token(type=TokenType.VARIABLE, value="x")]),
(".", [Token(type=TokenType.ERROR, value="number after dot was expected")]),
("1.", [Token(type=TokenType.ERROR, value="number after dot was expected")]),
(".1", [Token(type=TokenType.FLOAT, value=".1")]),
("3.14", [Token(type=TokenType.FLOAT, value="3.14")]),
(
"2 + 3",
[
Token(type=TokenType.FLOAT, value="2"),
Token(type=TokenType.OPERATOR, value="+"),
Token(type=TokenType.FLOAT, value="3"),
],
),
(
"x - 4.5",
[
Token(type=TokenType.VARIABLE, value="x"),
Token(type=TokenType.OPERATOR, value="-"),
Token(type=TokenType.FLOAT, value="4.5"),
],
),
(
"x - 4.5 * 2.34 + 5.2",
[
Token(type=TokenType.VARIABLE, value="x"),
Token(type=TokenType.OPERATOR, value="-"),
Token(type=TokenType.FLOAT, value="4.5"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.FLOAT, value="2.34"),
Token(type=TokenType.OPERATOR, value="+"),
Token(type=TokenType.FLOAT, value="5.2"),
],
),
(
"(x - 4.5) * (2.34 + 5.2)",
[
Token(type=TokenType.SEPARATOR, value="("),
Token(type=TokenType.VARIABLE, value="x"),
Token(type=TokenType.OPERATOR, value="-"),
Token(type=TokenType.FLOAT, value="4.5"),
Token(type=TokenType.SEPARATOR, value=")"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.SEPARATOR, value="("),
Token(type=TokenType.FLOAT, value="2.34"),
Token(type=TokenType.OPERATOR, value="+"),
Token(type=TokenType.FLOAT, value="5.2"),
Token(type=TokenType.SEPARATOR, value=")"),
],
),
(
"sin(x) * 2.0",
[
Token(type=TokenType.FUNCTION, value="sin"),
Token(type=TokenType.SEPARATOR, value="("),
Token(type=TokenType.VARIABLE, value="x"),
Token(type=TokenType.SEPARATOR, value=")"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.FLOAT, value="2.0"),
],
),
(
"3.14 * coz(x)",
[
Token(type=TokenType.FLOAT, value="3.14"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.ERROR, value="unknown function name 'coz'"),
],
),
(
"3.14 * cos(2.4 * x) ^ 0.5",
[
Token(type=TokenType.FLOAT, value="3.14"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.FUNCTION, value="cos"),
Token(type=TokenType.SEPARATOR, value="("),
Token(type=TokenType.FLOAT, value="2.4"),
Token(type=TokenType.OPERATOR, value="*"),
Token(type=TokenType.VARIABLE, value="x"),
Token(type=TokenType.SEPARATOR, value=")"),
Token(type=TokenType.OPERATOR, value="^"),
Token(type=TokenType.FLOAT, value="0.5"),
],
),
],
)
def test_lexer(expression, expected):
assert list(lex(expression)) == expected
@pytest.mark.parametrize(
"expression, expected",
argvalues=[
("3.14", Atom(Token(type=TokenType.FLOAT, value="3.14"))),
(
"2 + 2",
InfixExpression(
operator="+",
lvalue=Atom(token=Token(type=TokenType.FLOAT, value="2")),
rvalue=Atom(token=Token(type=TokenType.FLOAT, value="2")),
),
),
(
"2 + 3 * 4 + 5",
InfixExpression(
operator="+",
lvalue=InfixExpression(
operator="+",
lvalue=Atom(Token(type=TokenType.FLOAT, value="2")),
rvalue=InfixExpression(
operator="*",
lvalue=Atom(Token(type=TokenType.FLOAT, value="3")),
rvalue=Atom(Token(type=TokenType.FLOAT, value="4")),
),
),
rvalue=Atom(Token(type=TokenType.FLOAT, value="5")),
),
),
(
"(2 + 3) * (4 + 5)",
InfixExpression(
operator="*",
lvalue=InfixExpression(
operator="+",
lvalue=Atom(Token(type=TokenType.FLOAT, value="2")),
rvalue=Atom(Token(type=TokenType.FLOAT, value="3")),
),
rvalue=InfixExpression(
operator="+",
lvalue=Atom(Token(type=TokenType.FLOAT, value="4")),
rvalue=Atom(Token(type=TokenType.FLOAT, value="5")),
),
),
),
(
"sin(x) + cos(x)",
InfixExpression(
operator="+",
lvalue=FunctionExpression(
function="sin",
argument=Atom(token=Token(type=TokenType.VARIABLE, value="x")),
),
rvalue=FunctionExpression(
function="cos",
argument=Atom(token=Token(type=TokenType.VARIABLE, value="x")),
),
),
),
],
)
def test_parser(expression, expected):
assert parse(expression) == expected
# Helper to create the desugared unary minus AST (0 - operand)
def _neg(operand):
return InfixExpression(
operator="-",
lvalue=Atom(Token(type=TokenType.FLOAT, value="0")),
rvalue=operand,
)
@pytest.mark.parametrize(
"expression, expected",
argvalues=[
# Simple unary minus: -x => 0 - x
(
"-x",
_neg(Atom(Token(type=TokenType.VARIABLE, value="x"))),
),
# Double negation: --x => 0 - (0 - x)
(
"--x",
_neg(_neg(Atom(Token(type=TokenType.VARIABLE, value="x")))),
),
# Subtract a negative: 1 - -2 => 1 - (0 - 2)
(
"1 - -2",
InfixExpression(
operator="-",
lvalue=Atom(Token(type=TokenType.FLOAT, value="1")),
rvalue=_neg(Atom(Token(type=TokenType.FLOAT, value="2"))),
),
),
# Negate function result: -sin(x) => 0 - sin(x)
(
"-sin(x)",
_neg(
FunctionExpression(
function="sin",
argument=Atom(Token(type=TokenType.VARIABLE, value="x")),
)
),
),
# Precedence: -2^3 should be -(2^3), not (-2)^3
# With binding power 3, unary minus binds looser than ^ (4,5)
(
"-2^3",
_neg(
InfixExpression(
operator="^",
lvalue=Atom(Token(type=TokenType.FLOAT, value="2")),
rvalue=Atom(Token(type=TokenType.FLOAT, value="3")),
)
),
),
# Explicit parens: (-2)^3 groups the negation first
(
"(-2)^3",
InfixExpression(
operator="^",
lvalue=_neg(Atom(Token(type=TokenType.FLOAT, value="2"))),
rvalue=Atom(Token(type=TokenType.FLOAT, value="3")),
),
),
],
)
def test_unary_minus(expression, expected):
assert parse(expression) == expected
@pytest.mark.parametrize(
"expression, x, expected",
[
("-x", 5, -5),
("--x", 5, 5),
("1 - -2", 0, 3),
("-2^3", 0, -8), # -(2^3) = -8
("(-2)^3", 0, -8), # (-2)^3 = -8
("-2^2", 0, -4), # -(2^2) = -4
("(-2)^2", 0, 4), # (-2)^2 = 4
],
)
def test_unary_minus_eval(expression, x, expected):
assert parse(expression).eval(x) == expected