[fine] fix some bugs, semantics for is

fine/src/parser.rs

@@ -1183,7 +1183,14 @@ fn field_list(p: &mut CParser) {
 
     p.expect_start(TokenKind::LeftBrace);
     while !p.at(TokenKind::RightBrace) && !p.eof() {
-        field_value(p);
+        if p.at(TokenKind::Identifier) {
+            field_value(p);
+        } else {
+            if p.at_any(STATEMENT_RECOVERY) {
+                break;
+            }
+            p.advance_with_error("expected an identifier in a field list");
+        }
     }
     p.expect(
         TokenKind::RightBrace,
@@ -1196,7 +1203,7 @@ fn field_list(p: &mut CParser) {
 fn field_value(p: &mut CParser) {
     let m = p.start();
 
-    p.expect(TokenKind::Identifier, "expected a field name");
+    p.expect_start(TokenKind::Identifier);
     if p.eat(TokenKind::Colon) {
         expression(p);
     }

fine/src/semantics.rs

@@ -604,14 +604,13 @@ impl<'a> Semantics<'a> {
         };
 
         let result = match tree.kind {
-            TreeKind::LetStatement => self.environment_of_let(parent, tree),
+            TreeKind::IsExpression => self.environment_of_is_expression(parent, tree),
-            TreeKind::ParamList => self.environment_of_paramlist(parent, tree),
-            TreeKind::File => self.environment_of_file(parent, tree),
             TreeKind::Block => self.environment_of_block(parent, tree),
-
+            TreeKind::File => self.environment_of_file(parent, tree),
             TreeKind::ForStatement => self.environment_of_for(parent, tree),
-
+            TreeKind::LetStatement => self.environment_of_let(parent, tree),
             TreeKind::MemberAccess => self.environment_of_member_access(tree),
+            TreeKind::ParamList => self.environment_of_paramlist(parent, tree),
 
             _ => parent,
         };
@@ -819,6 +818,24 @@ impl<'a> Semantics<'a> {
         }
     }
 
+    fn environment_of_is_expression(&self, parent: EnvironmentRef, tree: &Tree) -> EnvironmentRef {
+        assert_eq!(tree.kind, TreeKind::IsExpression);
+        let Some(binding) = tree.child_tree_of_kind(self.syntax_tree, TreeKind::VariableBinding)
+        else {
+            return parent;
+        };
+        let Some(variable) = binding.nth_token(0) else {
+            return Environment::error();
+        };
+        let Some(type_expr) = binding.nth_tree(2) else {
+            return Environment::error();
+        };
+
+        let mut env = Environment::new(Some(parent), Location::Local);
+        env.insert(variable, type_expr);
+        return EnvironmentRef::new(env);
+    }
+
     pub fn class_of(&self, t: TreeRef) -> ClassRef {
         {
             // I want to make sure that this borrow is dropped after this block.
@@ -968,6 +985,9 @@ impl<'a> Semantics<'a> {
             (Type::Error, _) => true,
             (_, Type::Error) => true,
 
+            // Can... I... convert unreachable always? Is this sound?
+            (Type::Unreachable, _) => true,
+
             // TODO: Unification on type variables! :D
             (_, _) => false,
         }
@@ -1010,6 +1030,7 @@ impl<'a> Semantics<'a> {
             TreeKind::GroupingExpression => self.type_of_grouping(tree),
             TreeKind::Identifier => self.type_of_identifier(t, tree),
             TreeKind::IfStatement => self.type_of_if_statement(tree),
+            TreeKind::IsExpression => Some(Type::Bool),
             TreeKind::LetStatement => Some(Type::Nothing),
             TreeKind::ListConstructor => self.type_of_list_constructor(t, tree),
             TreeKind::ListConstructorElement => self.type_of_list_constructor_element(tree),

fine/tests/expression/is.fine

@@ -0,0 +1,18 @@
+class Foo {
+  a: f64;
+}
+
+fun test() -> f64 {
+  let b = new Foo { a : 23 };
+
+  let result = 0;
+  if b is c:Foo and c.a == 23 {
+    result = result + 1;
+  }
+  if b is c:Foo and c.a == 24 {
+    result = result + 1;
+  }
+  result
+}
+
+// @no-errors

fine/tests/expression/return_expression.fine

@@ -0,0 +1,6 @@
+fun explicit_return() -> f64 {
+  return 10.0;
+  // No error: after this point code is unreachable.
+}
+
+// @no-errors