feat(core): add zero-width negation expression

harper-core/src/expr/mod.rs

@@ -23,6 +23,7 @@ mod first_match_of;
 mod fixed_phrase;
 mod longest_match_of;
 mod mergeable_words;
+mod not;
 mod optional;
 mod pronoun_be;
 mod reflexive_pronoun;
@@ -50,6 +51,7 @@ pub use first_match_of::FirstMatchOf;
 pub use fixed_phrase::FixedPhrase;
 pub use longest_match_of::LongestMatchOf;
 pub use mergeable_words::MergeableWords;
+pub use not::Not;
 pub use optional::Optional;
 pub use pronoun_be::PronounBe;
 pub use reflexive_pronoun::ReflexivePronoun;

harper-core/src/expr/not.rs

@@ -0,0 +1,74 @@
+use crate::{Span, Token};
+
+use super::Expr;
+
+/// A zero-width assertion that matches when its inner expression does not.
+pub struct Not {
+    inner: Box<dyn Expr>,
+}
+
+impl Not {
+    pub fn new(inner: impl Expr + 'static) -> Self {
+        Self {
+            inner: Box::new(inner),
+        }
+    }
+}
+
+impl Expr for Not {
+    fn run(&self, cursor: usize, tokens: &[Token], source: &[char]) -> Option<Span<Token>> {
+        self.inner
+            .run(cursor, tokens, source)
+            .is_none()
+            .then(|| Span::empty(cursor))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        Document,
+        expr::{AnchorStart, ExprExt, SequenceExpr},
+        linting::tests::SpanVecExt,
+    };
+
+    use super::Not;
+
+    #[test]
+    fn rejects_expression_at_start() {
+        let document = Document::new_plain_english_curated("Give the rise to power.");
+        let expression = SequenceExpr::with(Not::new(AnchorStart))
+            .then_any_capitalization_of("give")
+            .then_whitespace()
+            .then_any_capitalization_of("the")
+            .then_whitespace()
+            .then_any_capitalization_of("rise")
+            .then_whitespace()
+            .then_any_capitalization_of("to");
+
+        let matches = expression
+            .iter_matches_in_doc(&document)
+            .collect::<Vec<_>>();
+
+        assert!(matches.is_empty());
+    }
+
+    #[test]
+    fn matches_expression_after_start() {
+        let document = Document::new_plain_english_curated("They give the rise to power.");
+        let expression = SequenceExpr::with(Not::new(AnchorStart))
+            .then_any_capitalization_of("give")
+            .then_whitespace()
+            .then_any_capitalization_of("the")
+            .then_whitespace()
+            .then_any_capitalization_of("rise")
+            .then_whitespace()
+            .then_any_capitalization_of("to");
+
+        let matches = expression
+            .iter_matches_in_doc(&document)
+            .collect::<Vec<_>>();
+
+        assert_eq!(matches.to_strings(&document), ["give the rise to"]);
+    }
+}