1 files changed, 214 insertions, 2 deletions
diff --git a/src/checker.rs b/src/checker.rs
index ea099ab..a53a48a 100644
--- a/src/checker.rs
+++ b/src/checker.rs
@@ -1,7 +1,219 @@
-use crate::parser::*;
+use crate::ast::*;
+use tracing::{debug, instrument, trace};
 
+use derive_more::Display;
+use std::collections::HashMap;
+
+#[derive(Display)]
 pub enum CheckError {
+    #[display("Unbound: {_0}")]
     Unbound(String),
+    #[display("Duplicate field: {_0}")]
     DuplicateField(String),
-    ExpectedTypeFoundTerm(String),
+    #[display("Rebinding: {_0}")]
+    Rebinding(String),
+    #[display("The following functionality is unimplemented: {_0}")]
+    Unimplemented(String),
+}
+
+#[derive(Debug)]
+struct SetRef {
+    set: Set,
+    belongs_to: String,
+}
+
+#[derive(Debug)]
+struct ElRef {
+    set: Set,
+    belongs_to: String,
+}
+
+#[derive(Debug, Default)]
+struct CheckState {
+    sets: HashMap<String, Set>,
+    elements: HashMap<String, Element>,
+    record_fields: HashMap<String, SetRef>,
+    variant_fields: HashMap<String, SetRef>,
+    signatures: HashMap<String, Signature>,
+    instances: HashMap<String, Instance>,
+}
+
+impl CheckState {
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_set(&self, name: &String) -> Result<(), CheckError> {
+        if self.sets.contains_key(name) {
+            Err(CheckError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_record_field(&self, name: &String) -> Result<(), CheckError> {
+        if self.record_fields.contains_key(name) {
+            Err(CheckError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_variant_field(&self, name: &String) -> Result<(), CheckError> {
+        if self.variant_fields.contains_key(name) {
+            Err(CheckError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn assert_unbound_element(&self, name: &String) -> Result<(), CheckError> {
+        if self.elements.contains_key(name) {
+            Err(CheckError::Rebinding(name.clone()))
+        } else {
+            Ok(())
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn add_record_field(
+        &mut self,
+        name: &String,
+        set: &Set,
+        belongs_to: &String,
+    ) -> Result<(), CheckError> {
+        self.assert_unbound_record_field(name)?;
+        self.record_fields.insert(
+            name.clone(),
+            SetRef {
+                set: set.clone(),
+                belongs_to: belongs_to.clone(),
+            },
+        );
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn add_variant_field(
+        &mut self,
+        name: &String,
+        set: &Set,
+        belongs_to: &String,
+    ) -> Result<(), CheckError> {
+        self.assert_unbound_variant_field(name)?;
+        self.variant_fields.insert(
+            name.clone(),
+            SetRef {
+                set: set.clone(),
+                belongs_to: belongs_to.clone(),
+            },
+        );
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn add_set(&mut self, name: &String, set: &Set) -> Result<(), CheckError> {
+        self.assert_unbound_set(name)?;
+        match set {
+            Set::Record(fields) => {
+                for RecordField { name: rfn, set } in fields {
+                    self.add_record_field(rfn, set, name)?;
+                }
+            }
+            Set::Variant(fields) => {
+                for VariantField { name: vfn, set } in fields {
+                    self.add_variant_field(vfn, set, name)?;
+                }
+            }
+            _ => (),
+        };
+        self.sets.insert(name.clone(), set.clone());
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn add_element(&mut self, name: &String, element: &Element) -> Result<(), CheckError> {
+        self.assert_unbound_element(name)?;
+        self.elements.insert(name.clone(), element.clone());
+        Ok(())
+    }
+}
+
+impl CheckState {
+    #[instrument(skip(self, prog), level = "debug")]
+    pub fn check(&mut self, prog: &Programme) -> Result<(), CheckError> {
+        let Programme(decls) = prog;
+
+        for decl in decls {
+            debug!(%decl, "checking declaration");
+            match decl {
+                Decl::Set { name, set } => {
+                    self.assert_unbound_set(name)?;
+                    self.check_set(set)?;
+                    // One catch, prohibit "let .. X = X"
+                    if let Set::Var(v) = set
+                        && v == name
+                    {
+                        return Err(CheckError::Rebinding(v.clone()));
+                    };
+                    self.add_set(name, set)
+                }
+
+                Decl::Element { name, set, element } => {
+                    self.check_element(name, set, element)?;
+                    // TODO: don't drop the set?
+                    self.add_element(name, element)
+                }
+                Decl::Signature { name, signature } => Ok(()),
+                Decl::Instance {
+                    name,
+                    signature,
+                    instance,
+                } => Ok(()),
+            }?;
+        }
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn check_set(&self, set: &Set) -> Result<(), CheckError> {
+        match set {
+            Set::BuiltIn(_) => Ok(()),
+            Set::Record(fields) => self.check_record(fields),
+            Set::Variant(fields) => Err(CheckError::Unimplemented("variants".to_string())),
+            Set::ClaimedSet(instance) => {
+                Err(CheckError::Unimplemented("instances as sets".to_string()))
+            }
+            Set::Var(v) => {
+                if self.sets.contains_key(v) {
+                    Ok(())
+                } else {
+                    Err(CheckError::Unbound(v.clone()))
+                }
+            }
+        }
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn check_record(&self, fields: &Vec<RecordField>) -> Result<(), CheckError> {
+        for RecordField { name, set } in fields {
+            self.assert_unbound_record_field(name)?;
+            self.check_set(set)?;
+        }
+        Ok(())
+    }
+
+    #[instrument(skip(self), level = "debug")]
+    fn check_element(&self, name: &String, set: &Set, element: &Element) -> Result<(), CheckError> {
+        self.assert_unbound_element(name)?;
+        self.check_set(set)?;
+        Ok(())
+    }
+}
+
+impl Programme {
+    pub fn check(&self) -> Result<(), CheckError> {
+        let mut state = CheckState::default();
+        state.check(self)
+    }
 }