1 files changed, 233 insertions, 0 deletions
diff --git a/src/checker_state.rs b/src/checker_state.rs
new file mode 100644
index 0000000..c4b4a3a
--- /dev/null
+++ b/src/checker_state.rs
@@ -0,0 +1,233 @@
+use crate::ast::*;
+use tracing::instrument;
+
+use derive_more::Display;
+use std::collections::HashMap;
+use std::fmt;
+
+#[derive(Display)]
+pub enum CheckerError {
+    #[display("Unbound: {_0}")]
+    Unbound(String),
+    #[display("Rebinding: {_0}")]
+    Rebinding(String),
+    #[display("The following functionality is unimplemented: {_0}")]
+    Unimplemented(String),
+    #[display("Element claimed to belong to {_0} but actually belongs to {_1}")]
+    WrongSetForElement(Set, Set),
+    #[display("Element {element} does belong to set {claimed}: {reason}")]
+    ElementDoesNotBelong {
+        element: Element,
+        claimed: Set,
+        reason: String,
+    },
+    #[display("Case analysis {_0} does not have consistent set for scrutinee")]
+    IncosistentCaseScrutineeSet(Element),
+    #[display("Incomplete case analysis: covered [{}] but required [{}]",
+        found.join(", "),
+        required.join(", ")
+    )]
+    IncompleteCaseAnalysis {
+        found: Vec<String>,
+        required: Vec<String>,
+    },
+}
+
+#[derive(Display, Clone)]
+#[display("{field_set} @ {owner_set}")]
+pub struct SetField {
+    pub field_set: Set,
+    pub owner_set: Set,
+}
+
+#[derive(Display, Clone)]
+#[display("{element} : {set}")]
+pub struct CheckedElement {
+    pub element: Element,
+    pub set: Set,
+}
+
+#[derive(Default, Clone)]
+pub struct CheckerState {
+    wf_sets: HashMap<String, Set>,
+    wf_elements: HashMap<String, CheckedElement>,
+    wf_signatures: HashMap<String, Signature>,
+    wf_instances: HashMap<String, Instance>,
+    record_fields: HashMap<String, SetField>,
+    variant_fields: HashMap<String, SetField>,
+}
+
+impl fmt::Display for CheckerState {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fn section<K, V>(f: &mut fmt::Formatter<'_>, name: &str, map: &HashMap<K, V>) -> fmt::Result
+        where
+            K: fmt::Display + Ord,
+            V: fmt::Display,
+        {
+            writeln!(f, "  {name} = {{")?;
+            let mut entries: Vec<_> = map.iter().collect();
+            entries.sort_by(|a, b| a.0.cmp(b.0));
+            for (k, v) in entries {
+                writeln!(f, "    {k} ~> {v},")?;
+            }
+            writeln!(f, "  }},")
+        }
+
+        writeln!(f, "CheckState {{")?;
+        section(f, "sets", &self.wf_sets)?;
+        section(f, "elements", &self.wf_elements)?;
+        section(f, "record_fields", &self.record_fields)?;
+        section(f, "variant_fields", &self.variant_fields)?;
+        section(f, "signatures", &self.wf_signatures)?;
+        section(f, "instances", &self.wf_instances)?;
+        writeln!(f, " }}")?;
+        Ok(())
+    }
+}
+
+// The invariant we're maintaining is that everything is fully evaluated before
+// we commit it to be stored in the state.
+impl CheckerState {
+    // Because of our invariant we don't actually need to do anything
+    // non-trivial here.
+    #[instrument(skip(self), level = "debug", fields(%set_a, %set_b))]
+    pub fn set_equal(&self, set_a: &Set, set_b: &Set) -> bool {
+        set_a == set_b
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_set(&self, name: &String) -> Result<(), CheckerError> {
+        if self.wf_sets.contains_key(name) {
+            Err(CheckerError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_element(&self, name: &String) -> Result<(), CheckerError> {
+        if self.wf_elements.contains_key(name) {
+            Err(CheckerError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug", fields(%name, %set_ref, %belongs_to))]
+    fn assert_correct_owner(
+        &self,
+        name: &String,
+        set_ref: &SetField,
+        belongs_to: &Set,
+    ) -> Result<(), CheckerError> {
+        if !self.set_equal(&set_ref.owner_set, belongs_to) {
+            Err(CheckerError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug", fields(%name, %field_set, %owner_set))]
+    fn add_record_field(
+        &mut self,
+        name: &String,
+        field_set: &Set,
+        owner_set: &Set,
+    ) -> Result<(), CheckerError> {
+        if let Some(set_ref) = self.record_fields.get(name) {
+            self.assert_correct_owner(name, set_ref, owner_set)?;
+        };
+        self.record_fields.insert(
+            name.clone(),
+            SetField {
+                field_set: field_set.clone(),
+                owner_set: owner_set.clone(),
+            },
+        );
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug", fields(%name, %field_set, %owner_set))]
+    fn add_variant_field(
+        &mut self,
+        name: &String,
+        field_set: &Set,
+        owner_set: &Set,
+    ) -> Result<(), CheckerError> {
+        if let Some(set_ref) = self.variant_fields.get(name) {
+            self.assert_correct_owner(name, set_ref, owner_set)?;
+        };
+        self.variant_fields.insert(
+            name.clone(),
+            SetField {
+                field_set: field_set.clone(),
+                owner_set: owner_set.clone(),
+            },
+        );
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug", fields(%name, %set))]
+    pub fn add_set(&mut self, name: &String, set: Set) -> Result<(), CheckerError> {
+        self.assert_unbound_set(name)?;
+        match &set {
+            Set::Record(fields) => {
+                for RecordField {
+                    name: rfn,
+                    set: field_set,
+                } in fields
+                {
+                    self.add_record_field(rfn, field_set, &set)?;
+                }
+            }
+            Set::Variant(fields) => {
+                for VariantField {
+                    name: vfn,
+                    set: field_set,
+                } in fields
+                {
+                    self.add_variant_field(vfn, field_set, &set)?;
+                }
+            }
+            _ => (),
+        };
+        self.wf_sets.insert(name.clone(), set);
+        Ok(())
+    }
+
+    pub fn add_element(
+        &mut self,
+        name: String,
+        element: Element,
+        set: Set,
+    ) -> Result<(), CheckerError> {
+        self.assert_unbound_element(&name)?;
+        self.wf_elements
+            .insert(name, CheckedElement { element, set });
+        Ok(())
+    }
+
+    pub fn lookup_set(&self, name: &String) -> Result<&Set, CheckerError> {
+        self.wf_sets
+            .get(name)
+            .map_or(Err(CheckerError::Unbound(name.clone())), Ok)
+    }
+
+    pub fn lookup_element(&self, name: &String) -> Result<&CheckedElement, CheckerError> {
+        self.wf_elements
+            .get(name)
+            .map_or(Err(CheckerError::Unbound(name.clone())), Ok)
+    }
+
+    pub fn lookup_record_field(&self, name: &String) -> Result<&SetField, CheckerError> {
+        self.record_fields
+            .get(name)
+            .map_or(Err(CheckerError::Unbound(name.clone())), Ok)
+    }
+
+    pub fn lookup_variant_field(&self, name: &String) -> Result<&SetField, CheckerError> {
+        self.variant_fields
+            .get(name)
+            .map_or(Err(CheckerError::Unbound(name.clone())), Ok)
+    }
+}