Add VisitObj and Obj::accept(&self, ..) method

- VisitObj is for visiting object instances and dyn objects (and thus
  dynamically dispatching accept)
- Obj::accept method is used for dispatching to the specific visitor
  method
- GcMark ZST added for visiting/marking living objects

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/compile/block.rs

@@ -1,7 +1,6 @@
 use crate::{
     compile::{ctx::Ctx, error::*, ir},
-    syn::{ast::*, op::BinOp, span::*},
-    visit::*,
+    syn::ast::*,
 };
 
 // basic block
@@ -9,8 +8,39 @@ pub enum Block {
     Body(ir::Body),
     Blocks(Vec<Block>),
 }
-
 /*
+ * Current problem:
+ * Visiting a TranslateAst would generally return the IR directly per-function. However, returning
+ * a different value type per Acceptor would make it impossible to have &dyn Acceptor refs, which
+ * is needed for visitor-based GC.
+ *
+ * Ideas:
+ * - Remove Visit::Out return value, and instead expect that the acceptor implementation to report
+ *   anything new to its visitor. Visitors/acceptors that require returning an error should use
+ *   TryVisit and TryAccept.
+ *   - Doesn't play nicely with something that might want to return something else.
+ * - TranslateAst doesn't necessarily need to be a Visitor, except for the context
+ *   - Can we just fake it with TryFrom?
+ *      impl TryFrom<(&'_ mut Ctx, ast::Stmt)> for ir::Stmt { ... }
+ *
+ */
+
+trait ToIr<I> {
+    fn to_ir(&self, ctx: &mut Ctx) -> Result<I>;
+}
+
+trait FromAst<A>: Sized {
+    fn from_ast(other: &A, ctx: &mut Ctx) -> Result<Self>;
+}
+
+impl<I, A> FromAst<A> for I
+    where A: ToIr<I>
+{
+    fn from_ast(other: &A, ctx: &mut Ctx) -> Result<Self> {
+        other.to_ir(ctx)
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // TranslateAst
 ////////////////////////////////////////////////////////////////////////////////
@@ -25,27 +55,40 @@ impl<'c, 't> TranslateAst<'c, 't> {
         TranslateAst { ctx, text }
     }
 
-    pub fn translate(&mut self, _ast: &Vec<Stmt>) -> Result<Block> {
-        todo!()
-    }
-
-    fn visit_lhs_expr(&mut self, expr: &Expr) -> Result<ir::Lhs> {
-        match expr {
-            Expr::Bin(b) if b.op == BinOp::Dot => todo!(),
-            Expr::Base(BaseExpr {
-                kind: BaseExprKind::Ident,
-                ..
-            }) => {
-                let _name = expr.text_at(self.text);
-                //let name_id = self.ctx.
-                todo!()
-                //Ok(ir::Lhs::Name(
-            }
-            _ => Err(Error::InvalidLhs { span: expr.span() }),
+    pub fn translate(&mut self, ast: &Vec<Stmt>) -> Result<ir::Body> {
+        let mut body = Vec::new();
+        for stmt in ast.iter() {
+            body.push(stmt.to_ir(self.ctx)?);
         }
+        Ok(body)
     }
 }
 
+impl ToIr<ir::Stmt> for Stmt {
+    fn to_ir(&self, _ctx: &mut Ctx) -> Result<ir::Stmt> {
+        todo!()
+    }
+}
+
+impl ToIr<ir::Stmt> for AssignStmt {
+    fn to_ir(&self, _ctx: &mut Ctx) -> Result<ir::Stmt> {
+        todo!()
+    }
+}
+
+impl ToIr<ir::Expr> for Expr {
+    fn to_ir(&self, _ctx: &mut Ctx) -> Result<ir::Expr> {
+        todo!()
+    }
+}
+
+impl ToIr<ir::Lhs> for Expr {
+    fn to_ir(&self, _ctx: &mut Ctx) -> Result<ir::Lhs> {
+        todo!()
+    }
+}
+
+/*
 impl Visit<Stmt> for TranslateAst<'_, '_> {
     type Out = Result<ir::Stmt>;
 

src/main.rs

@@ -1,5 +1,5 @@
 #![allow(dead_code)]
-#![feature(unsize, coerce_unsized, new_uninit)]
+#![feature(unsize, coerce_unsized, new_uninit, box_into_pin)]
 
 #[macro_use] mod visit;
 mod compile;

src/mem/basic.rs

@@ -2,31 +2,20 @@ use crate::{
     mem::{gc::Gc, ptr::ObjCell},
     obj::prelude::*,
 };
-use std::ptr::NonNull;
+use std::pin::Pin;
 
 #[derive(Default)]
 pub struct BasicGc {
-    objects: Vec<Box<ObjCell<dyn Obj>>>,
+    objects: Vec<Pin<Box<ObjCell<dyn Obj>>>>,
 }
 
 impl Gc for BasicGc {
-    fn alloc<O: Obj + 'static>(&mut self, obj: O) -> ObjRef<O> {
-        let obj_cell = Box::new(ObjCell::new(obj));
-        let obj_ptr = &*obj_cell as *const _ as *mut _;
-        self.objects.push(obj_cell);
-        ObjRef::new(NonNull::new(obj_ptr).unwrap())
-    }
-
-    fn add_obj(&mut self, owned: Box<ObjCell<dyn Obj>>) {
+    fn add_obj(&mut self, owned: Pin<Box<ObjCell<dyn Obj>>>) {
         self.objects.push(owned);
     }
 
-    fn mark(&mut self, _alive: &[DynRef]) {
-        todo!()
-    }
-
     fn sweep(&mut self) {
-        todo!()
+        self.objects.retain(|cell| cell.is_marked())
     }
 }
 

src/mem/gc.rs

@@ -1,11 +1,56 @@
-use crate::{mem::ptr::ObjCell, obj::prelude::*, visit::{Accept, Visit},};
+use crate::{mem::ptr::ObjCell, obj::prelude::*};
+use std::pin::Pin;
 
 pub trait Gc {
-    fn alloc<O: Obj + 'static>(&mut self, obj: O) -> ObjRef<O>;
+    fn alloc<O: Obj + 'static>(&mut self, obj: O) -> ObjRef<O> {
+        let obj_cell = Box::pin(ObjCell::new(obj));
+        let obj_ptr = &*obj_cell as *const _ as *mut _;
+        self.add_obj(obj_cell);
+        ObjRef::new(std::ptr::NonNull::new(obj_ptr).unwrap())
+    }
 
-    fn add_obj(&mut self, owned: Box<ObjCell<dyn Obj>>);
+    fn add_obj(&mut self, owned: Pin<Box<ObjCell<dyn Obj>>>);
 
-    fn mark(&mut self, alive: &[DynRef]);
+    fn mark(&mut self, alive: &[DynRef]) {
+        alive.iter()
+            .copied()
+            .for_each(|obj| GcMark.visit(obj));
+    }
 
     fn sweep(&mut self);
 }
+
+pub struct GcMark;
+
+impl VisitObj for GcMark {
+    fn visit(&mut self, obj: DynRef) {
+        if obj.is_marked() {
+            return;
+        }
+        obj.set_marked(true);
+        obj.borrow().accept(self)
+    }
+
+    fn visit_attrs(&mut self, attrs: &Attrs) {
+        attrs.inner()
+            .values()
+            .copied()
+            .for_each(|obj| {
+                self.visit(obj);
+            });
+    }
+
+    fn visit_dict(&mut self, d: &Dict) {
+        d.dict()
+            .iter()
+            .for_each(|(k, v)| {
+                self.visit(*k);
+                self.visit(*v);
+            });
+        self.visit(d.attrs());
+    } 
+
+    fn visit_str(&mut self, s: &Str) {
+        self.visit(s.attrs())
+    }
+}

src/mem/ptr.rs

@@ -1,7 +1,7 @@
 use crate::obj::Obj;
 use std::{
     any,
-    cell::RefCell,
+    cell::{Cell, RefCell},
     fmt::{self, Debug, Formatter},
     marker::Unsize,
     ops::{CoerceUnsized, Deref},
@@ -51,7 +51,7 @@ impl<O> Deref for ObjRef<O>
 where
     O: Obj + ?Sized,
 {
-    type Target = RefCell<O>;
+    type Target = ObjCell<O>;
 
     fn deref(&self) -> &Self::Target {
         // Safe, so long as there are no dangling pointers from the GC
@@ -140,22 +140,34 @@ where
 {
 }
 
-//
+////////////////////////////////////////////////////////////////////////////////
 // ObjCell
-//
+////////////////////////////////////////////////////////////////////////////////
 #[derive(Debug, Clone)]
 pub struct ObjCell<O: Obj + ?Sized> {
+    marked: Cell<bool>,
     cell: RefCell<O>,
 }
 
 impl<O: Obj> ObjCell<O> {
     pub fn new(obj: O) -> Self {
         ObjCell {
+            marked: Cell::new(false),
             cell: RefCell::new(obj),
         }
     }
 }
 
+impl<O: Obj + ?Sized> ObjCell<O> {
+    pub fn is_marked(&self) -> bool {
+        self.marked.get()
+    }
+
+    pub fn set_marked(&self, marked: bool) {
+        self.marked.set(marked);
+    }
+}
+
 impl<O: Obj + ?Sized> Deref for ObjCell<O> {
     type Target = RefCell<O>;
 

src/obj/attrs.rs

@@ -1,7 +1,6 @@
 use crate::{
     mem::ptr::{DynRef, ObjCell},
     obj::prelude::*,
-    visit::Visit,
 };
 use std::{
     cell::Cell,
@@ -42,10 +41,14 @@ impl Attrs {
         };
 
         // Add the object to the allocator pool
-        gc.add_obj(obj);
+        gc.add_obj(Box::into_pin(obj));
         obj_ref
     }
 
+    pub fn inner(&self) -> &Ss {
+        &self.attrs
+    }
+
     pub fn insert(&mut self, sym: Sym, value: DynRef) -> Option<DynRef> {
         self.attrs.insert(sym, value)
     }
@@ -64,17 +67,8 @@ impl Obj for Attrs {
     fn as_any(&self) -> &dyn std::any::Any {
         self
     }
-}
 
-/*
-impl_accept!(Attrs);
-
-impl<G: Gc> Visit<Attrs> for G {
-    type Out = ();
-
-    fn visit(&mut self, attrs: &Attrs) -> Self::Out {
-        attrs.attrs.values()
-            .for_each(|obj| obj.accept(self));
+    fn accept(&self, visitor: &mut dyn VisitObj) {
+        visitor.visit_attrs(self);
     }
 }
-*/

src/obj/dict.rs

@@ -1,12 +1,11 @@
-use crate::{obj::prelude::*, visit::Visit};
-use std::{any::Any, cell::Cell};
+use crate::obj::prelude::*;
+use std::any::Any;
 
 pub type DictRef = ObjRef<Dict>;
 
 pub struct Dict {
     dict: Vec<(DynRef, DynRef)>,
     attrs: ObjRef<Attrs>,
-    marked: Cell<bool>,
 }
 
 impl Dict {
@@ -14,9 +13,16 @@ impl Dict {
         Dict {
             dict: Default::default(),
             attrs,
-            marked: Cell::new(false),
         }
     }
+
+    pub fn dict(&self) -> &Vec<(DynRef, DynRef)> {
+        &self.dict
+    }
+
+    pub fn dict_mut(&mut self) -> &mut Vec<(DynRef, DynRef)> {
+        &mut self.dict
+    }
 }
 
 impl Obj for Dict {
@@ -27,4 +33,8 @@ impl Obj for Dict {
     fn as_any(&self) -> &dyn Any {
         self
     }
+
+    fn accept(&self, visitor: &mut dyn VisitObj) {
+        visitor.visit_dict(self);
+    }
 }

src/obj/fun.rs

@@ -27,6 +27,10 @@ impl Obj for NativeFun {
     fn as_any(&self) -> &dyn std::any::Any {
         self
     }
+
+    fn accept(&self, _: &mut dyn VisitObj) {
+        todo!("visit NativeFun");
+    }
 }
 
 pub struct Fun {
@@ -57,4 +61,8 @@ impl Obj for Fun {
     fn as_any(&self) -> &dyn Any {
         self
     }
+
+    fn accept(&self, _: &mut dyn VisitObj) {
+        todo!("visit Fun");
+    }
 }

src/obj/mod.rs

@@ -20,6 +20,7 @@ pub mod ns {
 }
 pub mod str;
 pub mod sym;
+pub mod visit;
 
 pub mod prelude {
     pub use crate::{
@@ -30,7 +31,7 @@ pub mod prelude {
         },
         obj::{
             Attrs, AttrsRef, Dict, DictRef, Fun, NameId, NativeFun, Ns, Obj, ObjCtx, Ss, Str,
-            StrRef, Sym,
+            StrRef, Sym, VisitObj,
         },
     };
 }
@@ -44,13 +45,14 @@ pub use self::{
     ns::{Ns, Ss},
     str::{Str, StrRef},
     sym::Sym,
+    visit::VisitObj,
 };
 use crate::mem::ptr::ObjRef;
-use crate::visit::*;
 use std::any::Any;
 
 pub trait Obj {
     fn attrs(&self) -> ObjRef<Attrs>;
     fn as_any(&self) -> &dyn Any;
-}
 
+    fn accept(&self, visitor: &mut dyn VisitObj);
+}

src/obj/str.rs

@@ -1,6 +1,6 @@
-use crate::{obj::prelude::*, visit::Visit};
+use crate::obj::prelude::*;
 use derivative::Derivative;
-use std::{any::Any, cell::Cell};
+use std::any::Any;
 
 pub type StrRef = ObjRef<Str>;
 
@@ -11,18 +11,11 @@ pub struct Str {
     attrs: AttrsRef,
 
     contents: String,
-
-    #[derivative(PartialEq = "ignore", PartialOrd = "ignore", Ord = "ignore")]
-    marked: Cell<bool>,
 }
 
 impl Str {
     pub fn new<G: Gc>(attrs: AttrsRef, contents: String) -> Self {
-        Str {
-            attrs,
-            contents,
-            marked: Cell::new(false),
-        }
+        Str { attrs, contents }
     }
 
     pub fn contents(&self) -> &String {
@@ -38,4 +31,8 @@ impl Obj for Str {
     fn as_any(&self) -> &dyn Any {
         self
     }
+
+    fn accept(&self, visitor: &mut dyn VisitObj) {
+        visitor.visit_str(self);
+    }
 }

src/obj/visit.rs

@@ -0,0 +1,14 @@
+use crate::obj::prelude::*;
+
+pub trait VisitObj {
+    fn visit(&mut self, obj: DynRef) where Self: Sized {
+        obj.borrow().accept(self)
+    }
+
+    fn visit_attrs(&mut self, attrs: &Attrs); 
+
+    fn visit_str(&mut self, s: &Str);
+
+    fn visit_dict(&mut self, d: &Dict);
+}
+