From f023d535d56e1f39655814474bb019edc307c80f Mon Sep 17 00:00:00 2001
From: Kasper <kasperkh.kh@gmail.com>
Date: Fri, 31 Jul 2026 10:01:53 +0200
Subject: [PATCH] Fix parsing of InchOfMercury

---
 CHANGELOG.md     |  1 +
 src/evaluator.rs |  4 ++++
 src/lexer.rs     | 48 +++++++++++++++++++++++++-----------------------
 3 files changed, 30 insertions(+), 23 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79a6880..d9e9096 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 - Add REPL to the `cpc` CLI
 - Add support for numbers with thousands separators `_`, ` ` and ` ` (thin space)
 - Format numbers with thousands separator
+- Fix parsing of `inch of mercury`
 
 ## 4.2.0 - 2026 Jul 1
 - Add ambiguous unit resolution depending on context and user locale.
diff --git a/src/evaluator.rs b/src/evaluator.rs
index fef10cd..89ee33a 100644
--- a/src/evaluator.rs
+++ b/src/evaluator.rs
@@ -489,6 +489,10 @@ mod tests {
 		eval_test("1 lbf to newtons", "4.4482216152605 newtons");
 		results_eq("1 bar to Pa", "100000 Pa");
 		results_eq("1 kHz to Hz", "1000 Hz");
+		results_eq("1 in of mercury", "1 inch of mercury");
+		results_eq("1 \" of mercury", "1 inch of mercury");
+		results_eq("1 \" of hg", "1 inch of mercury");
+		results_eq("1\"hg", "1 inch of mercury");
 		eval_test(
 			"1 km/h to m/s",
 			"≈ 0.277777777777777777777777777777777777778 meters / second",
diff --git a/src/lexer.rs b/src/lexer.rs
index bc88bf3..b29118b 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -165,14 +165,8 @@ fn lex_token(lexer: &mut Lexer) -> Result<(), String> {
 		"'" => Token::unit(Foot),
 		"\"" | "“" | "”" | "″" => {
 			lexer.graphemes.next();
-			match read_word(lexer).as_str() {
-				"hg" | "mercury" => Token::unit(InchOfMercury),
-				other => {
-					lexer.tokens.push(Token::unit(Inch));
-					lex_word_if_non_empty(other, lexer)?;
-					return Ok(());
-				}
-			}
+			lex_word(first_grapheme, lexer)?;
+			return Ok(());
 		}
 		grapheme => {
 			return Err(format!("Invalid character: {}", grapheme));
@@ -283,8 +277,29 @@ fn lex_word(word: &str, lexer: &mut Lexer) -> Result<(), String> {
 		"dm" | "decimeter" | "decimeters" | "decimetre" | "decimetres" => Token::unit(Decimeter),
 		"m" | "meter" | "meters" | "metre" | "metres" => Token::unit(Meter),
 		"km" | "kilometer" | "kilometers" | "kilometre" | "kilometres" => Token::unit(Kilometer),
-		"in" => Token::LexerKeyword(In),
-		"inch" | "inches" => Token::unit(Inch),
+		"\"" | "“" | "”" | "″" | "in" | "inch" | "inches" => {
+			match read_word(lexer).as_str() {
+				"of" => match read_word(lexer).as_str() {
+					"hg" | "mercury" => Token::unit(InchOfMercury),
+					other => {
+						lexer.tokens.push(Token::unit(Inch));
+						lexer.tokens.push(Token::TextOperator(Of));
+						lex_word_if_non_empty(other, lexer)?;
+						return Ok(());
+					}
+				},
+				"hg" if matches!(word, "\"" | "“" | "”" | "″") => Token::unit(InchOfMercury),
+				other => {
+					if word.to_ascii_lowercase() == "in" {
+						lexer.tokens.push(Token::LexerKeyword(In));
+					} else {
+						lexer.tokens.push(Token::unit(Inch));
+					}
+					lex_word_if_non_empty(other, lexer)?;
+					return Ok(());
+				}
+			}
+		}
 		"ft" | "foot" | "feet" => Token::unit(Foot),
 		"yd" | "yard" | "yards" => Token::unit(Yard),
 		"mi" | "mile" | "miles" => Token::unit(Mile),
@@ -880,19 +895,6 @@ pub fn lex(input: &str, remove_trailing_operator: bool) -> Result<Vec<Token>, St
 					}
 				}
 			}
-			// decide if "in" is Inch or To
-			Token::LexerKeyword(In) => {
-				match tokens.get(token_index + 1) {
-					Some(Token::Unit(_)) => {
-						// "in" should be To
-						tokens[token_index] = Token::TextOperator(To);
-					}
-					_ => {
-						// otherwise, Inch
-						tokens[token_index] = Token::unit(Inch);
-					}
-				}
-			}
 			_ => {}
 		}
 		if token_index == tokens.len() - 1 {
-- 
2.51.2