From 4862409b1d71f8268dfb5174cf534b789279190e Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Fri, 20 Dec 2019 19:44:19 +0100
Subject: [PATCH] add .foo record accessors

---
 src/can/expr.rs     | 31 +++++++++++++++++++++++++++++--
 tests/test_infer.rs |  5 +++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/can/expr.rs b/src/can/expr.rs
index b2c959bf40..061ab1ad4a 100644
--- a/src/can/expr.rs
+++ b/src/can/expr.rs
@@ -60,6 +60,8 @@ pub enum Expr {
 
     /// Look up exactly one field on a record, e.g. (expr).foo.
     Access(Box<Located<Expr>>, Box<str>),
+    /// field accessor as a function, e.g. (.foo) expr
+    Accessor(Box<str>),
 
     Tag(Box<str>, Vec<Expr>),
 
@@ -714,8 +716,33 @@ pub fn canonicalize_expr(
                 constraint,
             )
         }
-        ast::Expr::AccessorFunction(_)
-        | ast::Expr::If(_)
+        ast::Expr::AccessorFunction(field) => {
+            let ext_var = var_store.fresh();
+            let ext_type = Variable(ext_var);
+
+            let field_var = var_store.fresh();
+            let field_type = Variable(field_var);
+
+            let mut field_types = SendMap::default();
+            let field_name: Lowercase = (*field).into();
+            field_types.insert(field_name.clone(), field_type.clone());
+            let record_type = Type::Record(field_types, Box::new(ext_type));
+
+            (
+                Accessor(field_name.into()),
+                Output::default(),
+                exists(
+                    vec![field_var, ext_var],
+                    Eq(
+                        Type::Function(vec![record_type], Box::new(field_type)),
+                        expected,
+                        region,
+                    ),
+                ),
+            )
+        }
+
+        ast::Expr::If(_)
         | ast::Expr::GlobalTag(_)
         | ast::Expr::PrivateTag(_)
         | ast::Expr::MalformedIdent(_)
diff --git a/tests/test_infer.rs b/tests/test_infer.rs
index 9bac9d0c1a..a5f245cc2c 100644
--- a/tests/test_infer.rs
+++ b/tests/test_infer.rs
@@ -869,4 +869,9 @@ mod test_infer {
             "custom -> custom",
         );
     }
+
+    #[test]
+    fn accessor_function() {
+        infer_eq(".foo", "{ foo : a }* -> a");
+    }
 }