[fine] A lot more typing/environmenting, doing better on example

Time to start actual tests

fine/src/semantics.rs

@@ -634,11 +634,12 @@ impl<'a> Semantics<'a> {
         };
 
         let result = match tree.kind {
-            TreeKind::IsExpression => self.environment_of_is_expression(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::IsExpression => self.environment_of_is_expression(parent, tree),
             TreeKind::LetStatement => self.environment_of_let(parent, tree),
+            TreeKind::MatchArm => self.environment_of_match_arm(parent, t, tree),
             TreeKind::MemberAccess => self.environment_of_member_access(tree),
             TreeKind::ParamList => self.environment_of_paramlist(parent, tree),
 
@@ -865,6 +866,45 @@ impl<'a> Semantics<'a> {
         self.environment_of_pattern(parent, pattern, lhs)
     }
 
+    fn environment_of_match_arm(
+        &self,
+        parent: EnvironmentRef,
+        t: TreeRef,
+        tree: &Tree,
+    ) -> EnvironmentRef {
+        assert_eq!(tree.kind, TreeKind::MatchArm);
+
+        // The environment of a `match arm` expression is the environment produced by the pattern.
+        let Some(pattern) = tree.child_tree_of_kind(self.syntax_tree, TreeKind::Pattern) else {
+            // Should really have a pattern in there; otherwise there was a
+            // parse error, don't make more trouble.
+            return Environment::error();
+        };
+
+        // The expression in the match expression is the binding for the wildcard pattern.
+        // If we are somewhere weird then... uh....
+        let Some(match_body) = tree.parent else {
+            self.internal_compiler_error(Some(t), "no parent on match arm");
+        };
+        let match_body = &self.syntax_tree[match_body];
+        if match_body.kind != TreeKind::MatchBody {
+            self.internal_compiler_error(Some(t), "match arm parent not match body");
+        }
+        let Some(match_expression) = match_body.parent else {
+            self.internal_compiler_error(Some(t), "no parent on match body");
+        };
+        let match_expression = &self.syntax_tree[match_expression];
+        if match_expression.kind != TreeKind::MatchExpression {
+            self.internal_compiler_error(Some(t), "match body parent not match expression");
+        }
+
+        // The expression is the first tree child of match expression.
+        let Some(lhs) = tree.nth_tree(1) else {
+            return Environment::error();
+        };
+        self.environment_of_pattern(parent, pattern, lhs)
+    }
+
     // NOTE: THIS IS CALLED DIRECTLY, NOT VIA `environment_of` TO AVOID CYCLES.
     fn environment_of_pattern(
         &self,
@@ -1061,6 +1101,11 @@ impl<'a> Semantics<'a> {
             // Can... I... convert unreachable always? Is this sound?
             (Type::Unreachable, _) => true,
 
+            // Alternates convert if either side can convert.
+            (_, Type::Alternate(left, right)) => {
+                self.can_convert(from, left) || self.can_convert(from, right)
+            }
+
             // TODO: Unification on type variables! :D
             (_, _) => false,
         }
@@ -1120,6 +1165,10 @@ impl<'a> Semantics<'a> {
             TreeKind::TypeParameter => self.type_of_type_parameter(tree),
             TreeKind::UnaryExpression => self.type_of_unary(tree),
 
+            TreeKind::MatchExpression => self.type_of_match_expression(tree),
+            TreeKind::MatchBody => self.type_of_match_body(tree),
+            TreeKind::MatchArm => self.type_of_match_arm(tree),
+
             _ => self.internal_compiler_error(Some(t), "asking for a nonsense type"),
         };
 
@@ -1823,6 +1872,41 @@ impl<'a> Semantics<'a> {
         Some(Type::Alternate(Box::new(left), Box::new(right)))
     }
 
+    fn type_of_match_expression(&self, tree: &Tree) -> Option<Type> {
+        Some(self.type_of(tree.child_of_kind(self.syntax_tree, TreeKind::MatchBody)?))
+    }
+
+    fn type_of_match_body(&self, tree: &Tree) -> Option<Type> {
+        let arms: Vec<_> = tree
+            .children_of_kind(self.syntax_tree, TreeKind::MatchArm)
+            .collect();
+
+        if arms.len() == 0 {
+            self.report_error_tree(tree, "a match expression must have at least one arm");
+            Some(Type::Error)
+        } else {
+            let mut actual_type = self.type_of(arms[0]);
+            for arm in &arms[1..] {
+                let arm_type = self.type_of(*arm);
+                if !self.can_convert(&arm_type, &actual_type) {
+                    if self.can_convert(&actual_type, &arm_type) {
+                        // New lowest-common-denominator type
+                        actual_type = arm_type;
+                    } else {
+                        self.report_error_tree_ref(*arm, format!("this arm produces a value of type {arm_type} which is incompatible with the general result type {actual_type}"));
+                    }
+                }
+            }
+
+            Some(actual_type)
+        }
+    }
+
+    fn type_of_match_arm(&self, tree: &Tree) -> Option<Type> {
+        // The type of a match arm is the type of the expression to the right.
+        Some(self.type_of(tree.nth_tree(2)?))
+    }
+
     pub fn dump_compiler_state(&self, tr: Option<TreeRef>) {
         eprintln!("Parsed the tree as:");
         eprintln!("\n{}", self.syntax_tree.dump(true));
@@ -1949,13 +2033,13 @@ pub fn check(s: &Semantics) {
             TreeKind::SelfParameter => {}
             TreeKind::SelfReference => {}
 
-            TreeKind::IsExpression => check_is_expression(s, tree),
-            TreeKind::VariableBinding => check_variable_binding(s, tree),
+            TreeKind::IsExpression => {}
+            TreeKind::VariableBinding => {}
             TreeKind::Pattern => check_pattern(s, tree),
             TreeKind::WildcardPattern => {}
 
-            TreeKind::MatchArm => {}
-            TreeKind::MatchBody => {}
+            TreeKind::MatchArm => check_match_arm(s, tree),
+            TreeKind::MatchBody => check_match_body(s, t, tree),
             TreeKind::MatchExpression => {}
         }
     }
@@ -2132,10 +2216,6 @@ fn check_class_declaration(s: &Semantics, tree: &Tree) {
     }
 }
 
-fn check_is_expression(_s: &Semantics, _tree: &Tree) {
-    // TODO
-}
-
 fn check_pattern(s: &Semantics, tree: &Tree) {
     // If there's an AND then it must produce a boolean.
     let and_index = tree.children.iter().position(|c| match c {
@@ -2156,9 +2236,22 @@ fn check_pattern(s: &Semantics, tree: &Tree) {
     }
 }
 
-fn check_variable_binding(_s: &Semantics, _tree: &Tree) {
-    // TODO
+fn check_match_body(s: &Semantics, t: TreeRef, tree: &Tree) {
+    let _ = s.type_of(t); // Checks arm count and compatibility.
+
+    let arms: Vec<_> = tree
+        .children_of_kind(s.syntax_tree, TreeKind::MatchArm)
+        .collect();
+
+    if arms.len() > 0 {
+        for arm in &arms[1..] {
+            // TODO: How do I know if it's complete?
+            // TODO: How do I know if it's redundant?
         }
+    }
+}
+
+fn check_match_arm(s: &Semantics, tree: &Tree) {}
 
 #[cfg(test)]
 mod tests {