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
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
//! Cypher parser: WHERE predicate tree (OR / XOR / AND / NOT / comparisons).
use super::super::ast::*;
use super::super::tokenizer::CypherToken;
use super::CypherParser;
use crate::datatypes::values::Value;
impl CypherParser {
pub(super) fn parse_where_clause(&mut self) -> Result<Clause, String> {
self.expect(&CypherToken::Where)?;
let predicate = self.parse_predicate()?;
Ok(Clause::Where(WhereClause { predicate }))
}
/// Parse predicate with OR as lowest precedence
pub(super) fn parse_predicate(&mut self) -> Result<Predicate, String> {
self.parse_or_predicate()
}
/// Parse OR expressions (lowest precedence)
pub(super) fn parse_or_predicate(&mut self) -> Result<Predicate, String> {
let mut left = self.parse_xor_predicate()?;
while self.check(&CypherToken::Or) {
self.advance();
let right = self.parse_xor_predicate()?;
left = Predicate::Or(Box::new(left), Box::new(right));
}
Ok(left)
}
/// Parse XOR expressions (precedence between OR and AND)
pub(super) fn parse_xor_predicate(&mut self) -> Result<Predicate, String> {
let mut left = self.parse_and_predicate()?;
while self.check(&CypherToken::Xor) {
self.advance();
let right = self.parse_and_predicate()?;
left = Predicate::Xor(Box::new(left), Box::new(right));
}
Ok(left)
}
/// Parse AND expressions
pub(super) fn parse_and_predicate(&mut self) -> Result<Predicate, String> {
let mut left = self.parse_not_predicate()?;
while self.check(&CypherToken::And) {
self.advance();
let right = self.parse_not_predicate()?;
left = Predicate::And(Box::new(left), Box::new(right));
}
Ok(left)
}
/// Parse NOT expressions
pub(super) fn parse_not_predicate(&mut self) -> Result<Predicate, String> {
if self.check(&CypherToken::Not) {
self.advance();
let inner = self.parse_not_predicate()?;
Ok(Predicate::Not(Box::new(inner)))
} else {
self.parse_comparison_predicate()
}
}
/// Parse comparison expressions and IS NULL/IS NOT NULL/IN
pub(super) fn parse_comparison_predicate(&mut self) -> Result<Predicate, String> {
// Check for EXISTS { pattern }
if self.check(&CypherToken::Exists) {
self.advance(); // consume EXISTS
if self.check(&CypherToken::LBrace) {
self.advance(); // consume {
let patterns = self.parse_exists_patterns()?;
// Check for optional WHERE clause inside EXISTS { MATCH ... WHERE ... }
let where_clause = if self.check(&CypherToken::Where) {
self.advance(); // consume WHERE
Some(Box::new(self.parse_predicate()?))
} else {
None
};
self.expect(&CypherToken::RBrace)?;
return Ok(Predicate::Exists {
patterns,
where_clause,
});
} else if self.check(&CypherToken::LParen) {
self.advance(); // consume outer (
// Support EXISTS((...)) — inner parens are the pattern
if self.check(&CypherToken::LParen) {
let pattern_str = self.extract_pattern_string()?;
let pattern =
crate::graph::core::pattern_matching::parse_pattern(&pattern_str)?;
self.expect(&CypherToken::RParen)?; // consume outer )
return Ok(Predicate::Exists {
patterns: vec![pattern],
where_clause: None,
});
} else if self.looks_like_property_access() {
// Neo4j-style `exists(n.prop)` for property-existence
// checks. KGLite doesn't support this form — point the
// user at the modern equivalent rather than the pattern
// error, which sends them down the wrong rabbit hole.
return Err(
"exists(n.prop) is Neo4j legacy syntax for property-existence. \
Use `WHERE n.prop IS NOT NULL` instead. \
(For pattern-existence, EXISTS takes a pattern: \
`EXISTS { (n)-[:REL]->() }` or `EXISTS((n)-[:REL]->())`.)"
.to_string(),
);
} else {
return Err("EXISTS(...) requires a pattern in parentheses, e.g. \
EXISTS((n)-[:REL]->()). For property-existence checks, \
use `WHERE n.prop IS NOT NULL` (Neo4j-style \
`exists(n.prop)` is not supported)."
.to_string());
}
} else {
return Err("Expected '{' or '(' after EXISTS".to_string());
}
}
// Check for parenthesized predicate
if self.check(&CypherToken::LParen) {
// Could be a parenthesized predicate or the start of a pattern
// Peek ahead to determine
if self.looks_like_pattern_start() {
// Inline pattern predicate — desugar to EXISTS { pattern }
let pattern_str = self.extract_pattern_string()?;
let pattern = crate::graph::core::pattern_matching::parse_pattern(&pattern_str)?;
return Ok(Predicate::Exists {
patterns: vec![pattern],
where_clause: None,
});
}
self.advance(); // consume (
let pred = self.parse_predicate()?;
self.expect(&CypherToken::RParen)?;
return Ok(pred);
}
let left = self.parse_expression()?;
// Label-check predicate: `WHERE n:Label` (and chained `n:A:B` = AND).
// Only applies when the LHS is a bare Variable — `count(n):Foo` isn't valid.
if self.check(&CypherToken::Colon) {
if let Expression::Variable(var) = &left {
let var = var.clone();
self.advance(); // consume :
let first_label = self.expect_name("label name after ':'")?;
let mut pred = Predicate::LabelCheck {
variable: var.clone(),
label: first_label,
};
while self.check(&CypherToken::Colon) {
self.advance();
let next_label = self.expect_name("label name after ':'")?;
pred = Predicate::And(
Box::new(pred),
Box::new(Predicate::LabelCheck {
variable: var.clone(),
label: next_label,
}),
);
}
return Ok(pred);
}
}
// parse_expression() may have already consumed IS NULL / IS NOT NULL
// and returned Expression::IsNull/IsNotNull — convert to Predicate form
if let Expression::IsNull(inner) = left {
return Ok(Predicate::IsNull(*inner));
}
if let Expression::IsNotNull(inner) = left {
return Ok(Predicate::IsNotNull(*inner));
}
// Check for IS NULL / IS NOT NULL (fallback for non-expression contexts)
if self.check(&CypherToken::Is) {
self.advance(); // consume IS
if self.check(&CypherToken::Not) {
self.advance(); // consume NOT
self.expect(&CypherToken::Null)?;
return Ok(Predicate::IsNotNull(left));
} else {
self.expect(&CypherToken::Null)?;
return Ok(Predicate::IsNull(left));
}
}
// Check for IN
if self.check(&CypherToken::In) {
self.advance();
if self.check(&CypherToken::LBracket) {
let list = self.parse_list_expression()?;
return Ok(Predicate::In { expr: left, list });
} else {
// IN with a variable, parameter, or function call expression
let list_expr = self.parse_expression()?;
return Ok(Predicate::InExpression {
expr: left,
list_expr,
});
}
}
// Check for STARTS WITH
if self.check(&CypherToken::StartsWith) {
self.advance(); // consume STARTS
// Expect WITH keyword (we use With token)
self.expect(&CypherToken::With)?;
let pattern = self.parse_expression()?;
return Ok(Predicate::StartsWith {
expr: left,
pattern,
});
}
// Check for ENDS WITH
if self.check(&CypherToken::EndsWith) {
self.advance(); // consume ENDS
self.expect(&CypherToken::With)?;
let pattern = self.parse_expression()?;
return Ok(Predicate::EndsWith {
expr: left,
pattern,
});
}
// Check for CONTAINS
if self.check(&CypherToken::Contains) {
self.advance();
let pattern = self.parse_expression()?;
return Ok(Predicate::Contains {
expr: left,
pattern,
});
}
// Check for comparison operator
let operator = match self.peek() {
Some(CypherToken::Equals) => ComparisonOp::Equals,
Some(CypherToken::NotEquals) => ComparisonOp::NotEquals,
Some(CypherToken::LessThan) => ComparisonOp::LessThan,
Some(CypherToken::LessThanEquals) => ComparisonOp::LessThanEq,
Some(CypherToken::GreaterThan) => ComparisonOp::GreaterThan,
Some(CypherToken::GreaterThanEquals) => ComparisonOp::GreaterThanEq,
Some(CypherToken::RegexMatch) => ComparisonOp::RegexMatch,
_ => {
// No operator - the expression itself is a boolean predicate
// Convert expression to a comparison: expr <> false (truthy check)
return Ok(Predicate::Comparison {
left: left.clone(),
operator: ComparisonOp::NotEquals,
right: Expression::Literal(Value::Boolean(false)),
});
}
};
self.advance(); // consume operator
let right = self.parse_expression()?;
Ok(Predicate::Comparison {
left,
operator,
right,
})
}
/// Parse a [value, value, ...] list for IN clause
pub(super) fn parse_list_expression(&mut self) -> Result<Vec<Expression>, String> {
self.expect(&CypherToken::LBracket)?;
let mut items = Vec::new();
if !self.check(&CypherToken::RBracket) {
items.push(self.parse_expression()?);
while self.check(&CypherToken::Comma) {
self.advance();
items.push(self.parse_expression()?);
}
}
self.expect(&CypherToken::RBracket)?;
Ok(items)
}
/// True when the next three tokens are `<ident> . <ident>` — i.e. the
/// shape of a property access (`n.prop`). Used by `parse_comparison_predicate`
/// to recognise the Neo4j-legacy `exists(n.prop)` form and steer the
/// user to `IS NOT NULL` instead of the generic pattern-required error.
pub(super) fn looks_like_property_access(&self) -> bool {
matches!(self.peek(), Some(CypherToken::Identifier(_)))
&& matches!(self.peek_at(1), Some(CypherToken::Dot))
&& matches!(self.peek_at(2), Some(CypherToken::Identifier(_)))
}
/// Quick lookahead to check if ( starts a pattern (node pattern) vs a parenthesized predicate
pub(super) fn looks_like_pattern_start(&self) -> bool {
// Pattern: (var:Type), (:Type), (), (var)-[...]->()
// Predicate: (expr op expr), (NOT ...)
match self.peek_at(1) {
Some(CypherToken::RParen) => {
// () or (var) closed immediately — pattern if followed by - or <
matches!(
self.peek_at(2),
Some(CypherToken::Dash) | Some(CypherToken::LessThan)
)
}
Some(CypherToken::Colon) => true, // (:Type)
Some(CypherToken::Identifier(_)) => {
match self.peek_at(2) {
Some(CypherToken::Colon) => true, // (var:Type
Some(CypherToken::RParen) => {
// (var) — pattern if followed by - or < e.g. (p)-[:REL]->()
matches!(
self.peek_at(3),
Some(CypherToken::Dash) | Some(CypherToken::LessThan)
)
}
_ => false,
}
}
_ => false,
}
}
}