mathlex 0.3.2

Mathematical expression parser for LaTeX and plain text notation, producing a language-agnostic AST
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288

//! Tests for precedence correctness in serialization.
//!
//! Verifies that Display and ToLatex produce output that parses back
//! with the correct precedence and associativity.

use mathlex::{parse, parse_latex, BinaryOp, Expression, ToLatex, UnaryOp};

// Helper to create a variable expression
fn var(name: &str) -> Expression {
    Expression::Variable(name.to_string())
}

// Helper to create an integer expression
fn int(n: i64) -> Expression {
    Expression::Integer(n)
}

// =============================================================================
// Plain Text Precedence Tests
// =============================================================================

#[test]
fn test_unary_neg_of_sum() {
    // -(a + b) should serialize with parens and round-trip correctly
    let ast = Expression::Unary {
        op: UnaryOp::Neg,
        operand: Box::new(Expression::Binary {
            op: BinaryOp::Add,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
    };
    let s = ast.to_string();
    assert!(s.contains("("), "Should have parens: {}", s);
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "-(a+b) should round-trip");
}

#[test]
fn test_unary_neg_of_product() {
    // -(a * b) should serialize with parens
    let ast = Expression::Unary {
        op: UnaryOp::Neg,
        operand: Box::new(Expression::Binary {
            op: BinaryOp::Mul,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
    };
    let s = ast.to_string();
    assert!(s.contains("("), "Should have parens: {}", s);
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "-(a*b) should round-trip");
}

#[test]
fn test_power_left_associativity_needs_parens() {
    // (a^b)^c should serialize with parens (power is right-associative)
    let ast = Expression::Binary {
        op: BinaryOp::Pow,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Pow,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s = ast.to_string();
    assert!(s.contains("("), "Should have parens for (a^b)^c: {}", s);
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "(a^b)^c should round-trip");
}

#[test]
fn test_power_right_associativity_no_parens() {
    // a^(b^c) is natural right-associativity, no parens needed
    let ast = Expression::Binary {
        op: BinaryOp::Pow,
        left: Box::new(var("a")),
        right: Box::new(Expression::Binary {
            op: BinaryOp::Pow,
            left: Box::new(var("b")),
            right: Box::new(var("c")),
        }),
    };
    let s = ast.to_string();
    // May or may not have parens, but should round-trip
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "a^(b^c) should round-trip");
}

#[test]
fn test_sum_in_product_needs_parens() {
    // (a + b) * c needs parens around the sum
    let ast = Expression::Binary {
        op: BinaryOp::Mul,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Add,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s = ast.to_string();
    assert!(s.contains("("), "Should have parens: {}", s);
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "(a+b)*c should round-trip");
}

#[test]
fn test_product_in_sum_no_parens() {
    // a * b + c doesn't need parens (mul has higher precedence)
    let ast = Expression::Binary {
        op: BinaryOp::Add,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Mul,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s = ast.to_string();
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "a*b+c should round-trip");
}

#[test]
fn test_subtraction_associativity() {
    // (a - b) - c vs a - (b - c)
    // Left: (a - b) - c = a - b - c (left associative, no parens needed)
    let left_assoc = Expression::Binary {
        op: BinaryOp::Sub,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Sub,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s1 = left_assoc.to_string();
    let parsed1 = parse(&s1).unwrap();
    assert_eq!(left_assoc, parsed1, "(a-b)-c should round-trip");

    // Right: a - (b - c) needs explicit parens
    let right_assoc = Expression::Binary {
        op: BinaryOp::Sub,
        left: Box::new(var("a")),
        right: Box::new(Expression::Binary {
            op: BinaryOp::Sub,
            left: Box::new(var("b")),
            right: Box::new(var("c")),
        }),
    };
    let s2 = right_assoc.to_string();
    assert!(s2.contains("("), "a-(b-c) should have parens: {}", s2);
    let parsed2 = parse(&s2).unwrap();
    assert_eq!(right_assoc, parsed2, "a-(b-c) should round-trip");
}

#[test]
fn test_division_associativity() {
    // Similar to subtraction - division is left associative
    // a / (b / c) needs explicit parens
    let ast = Expression::Binary {
        op: BinaryOp::Div,
        left: Box::new(var("a")),
        right: Box::new(Expression::Binary {
            op: BinaryOp::Div,
            left: Box::new(var("b")),
            right: Box::new(var("c")),
        }),
    };
    let s = ast.to_string();
    assert!(s.contains("("), "a/(b/c) should have parens: {}", s);
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "a/(b/c) should round-trip");
}

#[test]
fn test_nested_unary() {
    // --a should round-trip
    let ast = Expression::Unary {
        op: UnaryOp::Neg,
        operand: Box::new(Expression::Unary {
            op: UnaryOp::Neg,
            operand: Box::new(var("a")),
        }),
    };
    let s = ast.to_string();
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "--a should round-trip");
}

#[test]
fn test_complex_precedence_chain() {
    // a + b * c^d should parse correctly without parens
    let ast = Expression::Binary {
        op: BinaryOp::Add,
        left: Box::new(var("a")),
        right: Box::new(Expression::Binary {
            op: BinaryOp::Mul,
            left: Box::new(var("b")),
            right: Box::new(Expression::Binary {
                op: BinaryOp::Pow,
                left: Box::new(var("c")),
                right: Box::new(var("d")),
            }),
        }),
    };
    let s = ast.to_string();
    let parsed = parse(&s).unwrap();
    assert_eq!(ast, parsed, "a + b * c^d should round-trip");
}

// =============================================================================
// LaTeX Precedence Tests
// =============================================================================

#[test]
fn test_latex_unary_neg_of_sum() {
    let ast = Expression::Unary {
        op: UnaryOp::Neg,
        operand: Box::new(Expression::Binary {
            op: BinaryOp::Add,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
    };
    let s = ast.to_latex();
    assert!(
        s.contains("(") || s.contains("\\left"),
        "Should have parens: {}",
        s
    );
    let parsed = parse_latex(&s).unwrap();
    assert_eq!(ast, parsed, "LaTeX -(a+b) should round-trip");
}

#[test]
fn test_latex_fraction_in_sum() {
    // a + (1/2) where 1/2 is a fraction
    let ast = Expression::Binary {
        op: BinaryOp::Add,
        left: Box::new(var("a")),
        right: Box::new(Expression::Binary {
            op: BinaryOp::Div,
            left: Box::new(int(1)),
            right: Box::new(int(2)),
        }),
    };
    let s = ast.to_latex();
    let parsed = parse_latex(&s).unwrap();
    assert_eq!(ast, parsed, "LaTeX a + frac should round-trip");
}

#[test]
fn test_latex_power_precedence() {
    // (a^b)^c needs parens
    let ast = Expression::Binary {
        op: BinaryOp::Pow,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Pow,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s = ast.to_latex();
    let parsed = parse_latex(&s).unwrap();
    assert_eq!(ast, parsed, "LaTeX (a^b)^c should round-trip");
}

#[test]
fn test_latex_mul_precedence() {
    // (a + b) \cdot c needs parens
    let ast = Expression::Binary {
        op: BinaryOp::Mul,
        left: Box::new(Expression::Binary {
            op: BinaryOp::Add,
            left: Box::new(var("a")),
            right: Box::new(var("b")),
        }),
        right: Box::new(var("c")),
    };
    let s = ast.to_latex();
    let parsed = parse_latex(&s).unwrap();
    assert_eq!(ast, parsed, "LaTeX (a+b)*c should round-trip");
}