[fine] Starting to bind

fine/src/parser.rs

@@ -138,7 +138,7 @@ pub enum TreeKind {
 
 pub struct Tree<'a> {
     pub kind: TreeKind,
-    pub parent: Option<TreeRef>,
+    pub parent: Option<TreeRef>, // TODO: Do we actually need this?
     pub start_pos: usize,
     pub end_pos: usize,
     pub children: Vec<Child<'a>>,

fine/src/semantics.rs

@@ -1,8 +1,8 @@
 use crate::{
     parser::{Child, SyntaxTree, Tree, TreeKind, TreeRef},
-    tokens::{Lines, TokenKind},
+    tokens::{Lines, Token, TokenKind},
 };
-use std::{cell::RefCell, collections::HashMap, fmt};
+use std::{cell::RefCell, collections::HashMap, fmt, rc::Rc};
 
 // TODO: An error should have:
 //
@@ -121,22 +121,126 @@ impl fmt::Display for Type {
     }
 }
 
+pub struct Declaration {
+    declaration_type: Type,
+}
+
+pub struct Environment {
+    parent: Option<EnvironmentRef>,
+    declarations: HashMap<Box<str>, Declaration>,
+}
+
+impl Environment {
+    pub fn new(parent: Option<EnvironmentRef>) -> Self {
+        Environment {
+            parent,
+            declarations: HashMap::new(),
+        }
+    }
+
+    pub fn bind(&self, token: &Token) -> Option<&Declaration> {
+        if let Some(decl) = self.declarations.get(token.as_str()) {
+            return Some(decl);
+        }
+
+        let mut current = &self.parent;
+        while let Some(env) = current {
+            if let Some(decl) = env.declarations.get(token.as_str()) {
+                return Some(decl);
+            }
+            current = &env.parent;
+        }
+
+        None
+    }
+}
+
+#[derive(Clone)]
+pub struct EnvironmentRef(Rc<Environment>);
+
+impl EnvironmentRef {
+    pub fn new(environment: Environment) -> Self {
+        EnvironmentRef(Rc::new(environment))
+    }
+}
+
+impl std::ops::Deref for EnvironmentRef {
+    type Target = Environment;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+fn set_logical_parents(parents: &mut Vec<Option<TreeRef>>, syntax_tree: &SyntaxTree, t: TreeRef) {
+    let tree = &syntax_tree[t];
+
+    // The default logical parent is the physical parent.
+    if parents.len() <= t.index() {
+        parents.resize(t.index() + 1, None);
+        parents[t.index()] = tree.parent.clone();
+    }
+
+    for child in &tree.children {
+        match child {
+            Child::Token(_) => (),
+            Child::Tree(ct) => set_logical_parents(parents, syntax_tree, *ct),
+        }
+    }
+
+    match tree.kind {
+        TreeKind::Block => {
+            // In a block, each child actually points to the previous child
+            // as the logical parent, so that variable declarations that
+            // occur as part of statements in the block are available to
+            // statements later in the block.
+            let mut parent = Some(t);
+            for child in &tree.children {
+                match child {
+                    Child::Token(_) => (),
+                    Child::Tree(ct) => {
+                        parents[t.index()] = parent;
+                        parent = Some(*ct);
+                    }
+                }
+            }
+        }
+        _ => {}
+    }
+}
+
 pub struct Semantics<'a> {
     // TODO: Do I really want my own copy here? Should we standardize on Arc
     //       or Rc or some other nice sharing mechanism?
     syntax_tree: &'a SyntaxTree<'a>,
     lines: &'a Lines,
+
+    // Instead of physical parents, this is the set of *logical* parents.
+    // This is what is used for binding.
+    logical_parents: Vec<Option<TreeRef>>,
+
+    // TODO: State should be externalized instead of this refcell nonsense.
     errors: RefCell<Vec<Error>>,
     types: RefCell<HashMap<TreeRef, Type>>,
+    environments: RefCell<HashMap<TreeRef, EnvironmentRef>>,
+    empty_environment: EnvironmentRef,
 }
 
 impl<'a> Semantics<'a> {
     pub fn new(tree: &'a SyntaxTree<'a>, lines: &'a Lines) -> Self {
+        let mut logical_parents = Vec::new();
+        if let Some(root) = tree.root() {
+            set_logical_parents(&mut logical_parents, tree, root);
+        }
+
         let mut semantics = Semantics {
             syntax_tree: tree,
             lines,
+            logical_parents,
             errors: RefCell::new(vec![]),
             types: RefCell::new(HashMap::new()),
+            environments: RefCell::new(HashMap::new()),
+            empty_environment: EnvironmentRef::new(Environment::new(None)),
         };
 
         // NOTE: We ensure all the known errors are reported before we move
@@ -210,6 +314,26 @@ impl<'a> Semantics<'a> {
         }
     }
 
+    pub fn environment_of(&self, t: TreeRef) -> EnvironmentRef {
+        if let Some(existing) = self.environments.borrow().get(&t) {
+            return existing.clone();
+        }
+
+        let tree = &self.syntax_tree[t];
+        let parent = match self.logical_parents[t.index()] {
+            Some(t) => self.environment_of(t),
+            None => self.empty_environment.clone(),
+        };
+
+        let result = match tree.kind {
+            // TODO: Things that introduce an environment!
+            _ => parent,
+        };
+
+        self.environments.borrow_mut().insert(t, result.clone());
+        result
+    }
+
     pub fn type_of(&self, t: TreeRef) -> Option<Type> {
         if let Some(existing) = self.types.borrow().get(&t) {
             return Some(existing.clone());
@@ -491,6 +615,16 @@ impl<'a> Semantics<'a> {
 
     fn type_of_identifier(&self, tree: &Tree) -> Option<Type> {
         assert_eq!(tree.kind, TreeKind::Identifier);
+
+        let id = tree.nth_token(0)?;
+        if let Some(parent) = tree.parent {
+            let environment = self.environment_of(parent);
+            if let Some(declaration) = environment.bind(id) {
+                return Some(declaration.declaration_type);
+            }
+        }
+
+        self.report_error_tree(tree, format!("cannot find value {id} here"));
         Some(Type::Error)
     }
 }