From 9e7cd6fa97506f160ae400c2085c7c73950366e3 Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Mon, 16 Mar 2026 14:14:10 +0000
Subject: [PATCH] engine: expand default unit equivalences to match Vensim

Add dollar ($, Dollar, Dollars, $s) and generic unit (Unit, Units)
equivalence classes to the built-in unit aliases. These match the
default unit equivalences that Vensim ships with, improving
compatibility when importing Vensim models that use these units
without explicit equivalence declarations.

https://claude.ai/code/session_01SFHWDB5sKsuobFpi8wQhLP
---
 src/simlin-engine/src/units.rs | 48 ++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/src/simlin-engine/src/units.rs b/src/simlin-engine/src/units.rs
index 4283ff5ab..83794535c 100644
--- a/src/simlin-engine/src/units.rs
+++ b/src/simlin-engine/src/units.rs
@@ -80,7 +80,9 @@ impl Context {
         // These ensure that "person" and "people" (etc.) are treated as the same unit.
         // We only add a built-in if the model doesn't already define a unit with that name.
         let builtin_units: &[(&str, &[&str])] = &[
+            ("$", &["dollar", "dollars", "$s"]),
             ("person", &["people", "persons"]),
+            ("unit", &["units"]),
             ("minute", &["minutes"]),
             ("month", &["months"]),
             ("year", &["years", "yr", "yrs"]),
@@ -832,3 +834,49 @@ fn test_year_years_builtin_alias() {
     let result = build_unit_components(&context, &expr).unwrap();
     assert_eq!(result, expected_inverse, "1/yr should be 1/year");
 }
+
+#[test]
+fn test_builtin_dollar_equivalences() {
+    let context = Context::new_with_builtins(&[], &Default::default()).unwrap();
+
+    let expected: UnitMap = [("$".to_owned(), 1)].iter().cloned().collect();
+
+    let expr = Expr0::new("$", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "$ should parse correctly");
+
+    let expr = Expr0::new("Dollar", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "Dollar should resolve to $");
+
+    let expr = Expr0::new("Dollars", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "Dollars should resolve to $");
+
+    let expr = Expr0::new("$s", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "$s should resolve to $");
+
+    // Dollar/Dollars should cancel out
+    let expr = Expr0::new("Dollar/Dollars", LexerType::Units)
+        .unwrap()
+        .unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    let expected_dmnl: UnitMap = UnitMap::new();
+    assert_eq!(result, expected_dmnl, "Dollar/Dollars should cancel out");
+}
+
+#[test]
+fn test_builtin_unit_equivalences() {
+    let context = Context::new_with_builtins(&[], &Default::default()).unwrap();
+
+    let expected: UnitMap = [("unit".to_owned(), 1)].iter().cloned().collect();
+
+    let expr = Expr0::new("Unit", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "Unit should parse correctly");
+
+    let expr = Expr0::new("Units", LexerType::Units).unwrap().unwrap();
+    let result = build_unit_components(&context, &expr).unwrap();
+    assert_eq!(result, expected, "Units should resolve to unit");
+}