cl-ast: Add Fold and Visit traits, to more easily map or collect nodes in the AST

typeck.rs: Since this is apparently my testbed now, add a new mode.
TODO: replace the main `conlang` binary with this, since it's so much better.

cl-ast/src/ast_visitor.rs

@@ -0,0 +1,8 @@
+//! Contains an [immutable visitor](Visit) and an [owned folder](Fold) trait,
+//! with default implementations across the entire AST
+
+pub mod fold;
+pub mod visit;
+
+pub use fold::Fold;
+pub use visit::Visit;

cl-ast/src/ast_visitor/fold.rs

@@ -0,0 +1,493 @@
+//! A folder (implementer of the [Fold] trait) maps ASTs to ASTs
+
+use crate::ast::*;
+use cl_structures::span::Span;
+
+/// Deconstructs the entire AST, and reconstructs it from scratch.
+///
+/// Each method acts as a customization point.
+///
+/// There are a set of default implementations for enums
+/// under the name [`or_fold_`*](or_fold_expr_kind),
+/// provided for ease of use.
+///
+/// For all other nodes, traversal is *explicit*.
+pub trait Fold {
+    fn fold_span(&mut self, extents: Span) -> Span {
+        extents
+    }
+    fn fold_mutability(&mut self, mutability: Mutability) -> Mutability {
+        mutability
+    }
+    fn fold_visibility(&mut self, visibility: Visibility) -> Visibility {
+        visibility
+    }
+    fn fold_identifier(&mut self, ident: Identifier) -> Identifier {
+        ident
+    }
+    fn fold_literal(&mut self, lit: Literal) -> Literal {
+        or_fold_literal(self, lit)
+    }
+    fn fold_bool(&mut self, b: bool) -> bool {
+        b
+    }
+    fn fold_char(&mut self, c: char) -> char {
+        c
+    }
+    fn fold_int(&mut self, i: u128) -> u128 {
+        i
+    }
+    fn fold_string(&mut self, s: String) -> String {
+        s
+    }
+    fn fold_file(&mut self, f: File) -> File {
+        let File { items } = f;
+        File { items: items.into_iter().map(|i| self.fold_item(i)).collect() }
+    }
+    fn fold_attrs(&mut self, a: Attrs) -> Attrs {
+        let Attrs { meta } = a;
+        Attrs { meta: meta.into_iter().map(|m| self.fold_meta(m)).collect() }
+    }
+    fn fold_meta(&mut self, m: Meta) -> Meta {
+        let Meta { name, kind } = m;
+        Meta { name: self.fold_identifier(name), kind: self.fold_meta_kind(kind) }
+    }
+    fn fold_meta_kind(&mut self, kind: MetaKind) -> MetaKind {
+        or_fold_meta_kind(self, kind)
+    }
+    fn fold_item(&mut self, i: Item) -> Item {
+        let Item { extents, attrs, vis, kind } = i;
+        Item {
+            extents: self.fold_span(extents),
+            attrs: self.fold_attrs(attrs),
+            vis: self.fold_visibility(vis),
+            kind: self.fold_item_kind(kind),
+        }
+    }
+    fn fold_item_kind(&mut self, kind: ItemKind) -> ItemKind {
+        or_fold_item_kind(self, kind)
+    }
+    fn fold_alias(&mut self, a: Alias) -> Alias {
+        let Alias { to, from } = a;
+        Alias { to: self.fold_identifier(to), from: from.map(|from| Box::new(self.fold_ty(*from))) }
+    }
+    fn fold_const(&mut self, c: Const) -> Const {
+        let Const { name, ty, init } = c;
+        Const {
+            name: self.fold_identifier(name),
+            ty: Box::new(self.fold_ty(*ty)),
+            init: Box::new(self.fold_expr(*init)),
+        }
+    }
+    fn fold_static(&mut self, s: Static) -> Static {
+        let Static { mutable, name, ty, init } = s;
+        Static {
+            mutable: self.fold_mutability(mutable),
+            name: self.fold_identifier(name),
+            ty: Box::new(self.fold_ty(*ty)),
+            init: Box::new(self.fold_expr(*init)),
+        }
+    }
+    fn fold_module(&mut self, m: Module) -> Module {
+        let Module { name, kind } = m;
+        Module { name: self.fold_identifier(name), kind: self.fold_module_kind(kind) }
+    }
+    fn fold_module_kind(&mut self, m: ModuleKind) -> ModuleKind {
+        match m {
+            ModuleKind::Inline(f) => ModuleKind::Inline(self.fold_file(f)),
+            ModuleKind::Outline => ModuleKind::Outline,
+        }
+    }
+    fn fold_function(&mut self, f: Function) -> Function {
+        let Function { name, sign, bind, body } = f;
+        Function {
+            name: self.fold_identifier(name),
+            sign: self.fold_ty_fn(sign),
+            bind: bind.into_iter().map(|p| self.fold_param(p)).collect(),
+            body: body.map(|b| self.fold_block(b)),
+        }
+    }
+    fn fold_param(&mut self, p: Param) -> Param {
+        let Param { mutability, name } = p;
+        Param { mutability: self.fold_mutability(mutability), name: self.fold_identifier(name) }
+    }
+    fn fold_struct(&mut self, s: Struct) -> Struct {
+        let Struct { name, kind } = s;
+        Struct { name: self.fold_identifier(name), kind: self.fold_struct_kind(kind) }
+    }
+    fn fold_struct_kind(&mut self, kind: StructKind) -> StructKind {
+        match kind {
+            StructKind::Empty => StructKind::Empty,
+            StructKind::Tuple(tys) => {
+                StructKind::Tuple(tys.into_iter().map(|t| self.fold_ty(t)).collect())
+            }
+            StructKind::Struct(mem) => StructKind::Struct(
+                mem.into_iter()
+                    .map(|m| self.fold_struct_member(m))
+                    .collect(),
+            ),
+        }
+    }
+    fn fold_struct_member(&mut self, m: StructMember) -> StructMember {
+        let StructMember { vis, name, ty } = m;
+        StructMember {
+            vis: self.fold_visibility(vis),
+            name: self.fold_identifier(name),
+            ty: self.fold_ty(ty),
+        }
+    }
+    fn fold_enum(&mut self, e: Enum) -> Enum {
+        let Enum { name, kind } = e;
+        Enum { name: self.fold_identifier(name), kind: self.fold_enum_kind(kind) }
+    }
+    fn fold_enum_kind(&mut self, kind: EnumKind) -> EnumKind {
+        or_fold_enum_kind(self, kind)
+    }
+    fn fold_variant(&mut self, v: Variant) -> Variant {
+        let Variant { name, kind } = v;
+
+        Variant { name: self.fold_identifier(name), kind: self.fold_variant_kind(kind) }
+    }
+    fn fold_variant_kind(&mut self, kind: VariantKind) -> VariantKind {
+        or_fold_variant_kind(self, kind)
+    }
+    fn fold_impl(&mut self, i: Impl) -> Impl {
+        let Impl { target, body } = i;
+        Impl { target: self.fold_impl_kind(target), body: self.fold_file(body) }
+    }
+    fn fold_impl_kind(&mut self, kind: ImplKind) -> ImplKind {
+        or_fold_impl_kind(self, kind)
+    }
+    fn fold_ty(&mut self, t: Ty) -> Ty {
+        let Ty { extents, kind } = t;
+        Ty { extents: self.fold_span(extents), kind: self.fold_ty_kind(kind) }
+    }
+    fn fold_ty_kind(&mut self, kind: TyKind) -> TyKind {
+        or_fold_ty_kind(self, kind)
+    }
+    fn fold_ty_tuple(&mut self, t: TyTuple) -> TyTuple {
+        let TyTuple { types } = t;
+        TyTuple {
+            types: types
+                .into_iter()
+                .map(|kind| self.fold_ty_kind(kind))
+                .collect(),
+        }
+    }
+    fn fold_ty_ref(&mut self, t: TyRef) -> TyRef {
+        let TyRef { mutable, count, to } = t;
+        TyRef { mutable: self.fold_mutability(mutable), count, to: self.fold_path(to) }
+    }
+    fn fold_ty_fn(&mut self, t: TyFn) -> TyFn {
+        let TyFn { args, rety } = t;
+        TyFn {
+            args: Box::new(self.fold_ty_kind(*args)),
+            rety: rety.map(|t| Box::new(self.fold_ty(*t))),
+        }
+    }
+    fn fold_path(&mut self, p: Path) -> Path {
+        let Path { absolute, parts } = p;
+        Path { absolute, parts: parts.into_iter().map(|p| self.fold_path_part(p)).collect() }
+    }
+    fn fold_path_part(&mut self, p: PathPart) -> PathPart {
+        match p {
+            PathPart::SuperKw => PathPart::SuperKw,
+            PathPart::SelfKw => PathPart::SelfKw,
+            PathPart::Ident(i) => PathPart::Ident(self.fold_identifier(i)),
+        }
+    }
+    fn fold_stmt(&mut self, s: Stmt) -> Stmt {
+        let Stmt { extents, kind, semi } = s;
+        Stmt {
+            extents: self.fold_span(extents),
+            kind: self.fold_stmt_kind(kind),
+            semi: self.fold_semi(semi),
+        }
+    }
+    fn fold_stmt_kind(&mut self, kind: StmtKind) -> StmtKind {
+        or_fold_stmt_kind(self, kind)
+    }
+    fn fold_semi(&mut self, s: Semi) -> Semi {
+        s
+    }
+    fn fold_let(&mut self, l: Let) -> Let {
+        let Let { mutable, name, ty, init } = l;
+        Let {
+            mutable: self.fold_mutability(mutable),
+            name: self.fold_identifier(name),
+            ty: ty.map(|t| Box::new(self.fold_ty(*t))),
+            init: init.map(|e| Box::new(self.fold_expr(*e))),
+        }
+    }
+    fn fold_expr(&mut self, e: Expr) -> Expr {
+        let Expr { extents, kind } = e;
+        Expr { extents: self.fold_span(extents), kind: self.fold_expr_kind(kind) }
+    }
+    fn fold_expr_kind(&mut self, kind: ExprKind) -> ExprKind {
+        or_fold_expr_kind(self, kind)
+    }
+    fn fold_assign(&mut self, a: Assign) -> Assign {
+        let Assign { kind, parts } = a;
+        let (head, tail) = *parts;
+        Assign {
+            kind: self.fold_assign_kind(kind),
+            parts: Box::new((self.fold_expr_kind(head), self.fold_expr_kind(tail))),
+        }
+    }
+    fn fold_assign_kind(&mut self, kind: AssignKind) -> AssignKind {
+        kind
+    }
+    fn fold_binary(&mut self, b: Binary) -> Binary {
+        let Binary { kind, parts } = b;
+        let (head, tail) = *parts;
+        Binary {
+            kind: self.fold_binary_kind(kind),
+            parts: Box::new((self.fold_expr_kind(head), self.fold_expr_kind(tail))),
+        }
+    }
+    fn fold_binary_kind(&mut self, kind: BinaryKind) -> BinaryKind {
+        kind
+    }
+    fn fold_unary(&mut self, u: Unary) -> Unary {
+        let Unary { kind, tail } = u;
+        Unary { kind: self.fold_unary_kind(kind), tail: Box::new(self.fold_expr_kind(*tail)) }
+    }
+    fn fold_unary_kind(&mut self, kind: UnaryKind) -> UnaryKind {
+        kind
+    }
+    fn fold_index(&mut self, i: Index) -> Index {
+        let Index { head, indices } = i;
+        Index {
+            head: Box::new(self.fold_expr_kind(*head)),
+            indices: indices.into_iter().map(|e| self.fold_expr(e)).collect(),
+        }
+    }
+    fn fold_array(&mut self, a: Array) -> Array {
+        let Array { values } = a;
+        Array { values: values.into_iter().map(|e| self.fold_expr(e)).collect() }
+    }
+    fn fold_array_rep(&mut self, a: ArrayRep) -> ArrayRep {
+        let ArrayRep { value, repeat } = a;
+        ArrayRep {
+            value: Box::new(self.fold_expr_kind(*value)),
+            repeat: Box::new(self.fold_expr_kind(*repeat)),
+        }
+    }
+    fn fold_addrof(&mut self, a: AddrOf) -> AddrOf {
+        let AddrOf { count, mutable, expr } = a;
+        AddrOf {
+            count,
+            mutable: self.fold_mutability(mutable),
+            expr: Box::new(self.fold_expr_kind(*expr)),
+        }
+    }
+    fn fold_block(&mut self, b: Block) -> Block {
+        let Block { stmts } = b;
+        Block { stmts: stmts.into_iter().map(|s| self.fold_stmt(s)).collect() }
+    }
+    fn fold_group(&mut self, g: Group) -> Group {
+        let Group { expr } = g;
+        Group { expr: Box::new(self.fold_expr_kind(*expr)) }
+    }
+    fn fold_tuple(&mut self, t: Tuple) -> Tuple {
+        let Tuple { exprs } = t;
+        Tuple { exprs: exprs.into_iter().map(|e| self.fold_expr(e)).collect() }
+    }
+    fn fold_loop(&mut self, l: Loop) -> Loop {
+        let Loop { body } = l;
+        Loop { body: Box::new(self.fold_expr(*body)) }
+    }
+    fn fold_while(&mut self, w: While) -> While {
+        let While { cond, pass, fail } = w;
+        While {
+            cond: Box::new(self.fold_expr(*cond)),
+            pass: Box::new(self.fold_block(*pass)),
+            fail: self.fold_else(fail),
+        }
+    }
+    fn fold_if(&mut self, i: If) -> If {
+        let If { cond, pass, fail } = i;
+        If {
+            cond: Box::new(self.fold_expr(*cond)),
+            pass: Box::new(self.fold_block(*pass)),
+            fail: self.fold_else(fail),
+        }
+    }
+    fn fold_for(&mut self, f: For) -> For {
+        let For { bind, cond, pass, fail } = f;
+        For {
+            bind: self.fold_identifier(bind),
+            cond: Box::new(self.fold_expr(*cond)),
+            pass: Box::new(self.fold_block(*pass)),
+            fail: self.fold_else(fail),
+        }
+    }
+    fn fold_else(&mut self, e: Else) -> Else {
+        let Else { body } = e;
+        Else { body: body.map(|e| Box::new(self.fold_expr(*e))) }
+    }
+    fn fold_break(&mut self, b: Break) -> Break {
+        let Break { body } = b;
+        Break { body: body.map(|e| Box::new(self.fold_expr(*e))) }
+    }
+    fn fold_return(&mut self, r: Return) -> Return {
+        let Return { body } = r;
+        Return { body: body.map(|e| Box::new(self.fold_expr(*e))) }
+    }
+    fn fold_continue(&mut self, c: Continue) -> Continue {
+        let Continue = c;
+        Continue
+    }
+}
+
+#[inline]
+/// Folds a [Literal] in the default way
+pub fn or_fold_literal<F: Fold + ?Sized>(folder: &mut F, lit: Literal) -> Literal {
+    match lit {
+        Literal::Bool(b) => Literal::Bool(folder.fold_bool(b)),
+        Literal::Char(c) => Literal::Char(folder.fold_char(c)),
+        Literal::Int(i) => Literal::Int(folder.fold_int(i)),
+        Literal::String(s) => Literal::String(folder.fold_string(s)),
+    }
+}
+
+#[inline]
+/// Folds a [MetaKind] in the default way
+pub fn or_fold_meta_kind<F: Fold + ?Sized>(folder: &mut F, kind: MetaKind) -> MetaKind {
+    match kind {
+        MetaKind::Plain => MetaKind::Plain,
+        MetaKind::Equals(l) => MetaKind::Equals(folder.fold_literal(l)),
+        MetaKind::Func(lits) => {
+            MetaKind::Func(lits.into_iter().map(|l| folder.fold_literal(l)).collect())
+        }
+    }
+}
+
+#[inline]
+/// Folds an [ItemKind] in the default way
+pub fn or_fold_item_kind<F: Fold + ?Sized>(folder: &mut F, kind: ItemKind) -> ItemKind {
+    match kind {
+        ItemKind::Module(m) => ItemKind::Module(folder.fold_module(m)),
+        ItemKind::Alias(a) => ItemKind::Alias(folder.fold_alias(a)),
+        ItemKind::Enum(e) => ItemKind::Enum(folder.fold_enum(e)),
+        ItemKind::Struct(s) => ItemKind::Struct(folder.fold_struct(s)),
+        ItemKind::Const(c) => ItemKind::Const(folder.fold_const(c)),
+        ItemKind::Static(s) => ItemKind::Static(folder.fold_static(s)),
+        ItemKind::Function(f) => ItemKind::Function(folder.fold_function(f)),
+        ItemKind::Impl(i) => ItemKind::Impl(folder.fold_impl(i)),
+    }
+}
+
+#[inline]
+/// Folds a [ModuleKind] in the default way
+pub fn or_fold_module_kind<F: Fold + ?Sized>(folder: &mut F, kind: ModuleKind) -> ModuleKind {
+    match kind {
+        ModuleKind::Inline(f) => ModuleKind::Inline(folder.fold_file(f)),
+        ModuleKind::Outline => ModuleKind::Outline,
+    }
+}
+
+#[inline]
+/// Folds a [StructKind] in the default way
+pub fn or_fold_struct_kind<F: Fold + ?Sized>(folder: &mut F, kind: StructKind) -> StructKind {
+    match kind {
+        StructKind::Empty => StructKind::Empty,
+        StructKind::Tuple(tys) => {
+            StructKind::Tuple(tys.into_iter().map(|t| folder.fold_ty(t)).collect())
+        }
+        StructKind::Struct(mem) => StructKind::Struct(
+            mem.into_iter()
+                .map(|m| folder.fold_struct_member(m))
+                .collect(),
+        ),
+    }
+}
+
+#[inline]
+/// Folds an [EnumKind] in the default way
+pub fn or_fold_enum_kind<F: Fold + ?Sized>(folder: &mut F, kind: EnumKind) -> EnumKind {
+    match kind {
+        EnumKind::NoVariants => EnumKind::NoVariants,
+        EnumKind::Variants(v) => {
+            EnumKind::Variants(v.into_iter().map(|v| folder.fold_variant(v)).collect())
+        }
+    }
+}
+
+#[inline]
+/// Folds a [VariantKind] in the default way
+pub fn or_fold_variant_kind<F: Fold + ?Sized>(folder: &mut F, kind: VariantKind) -> VariantKind {
+    match kind {
+        VariantKind::Plain => VariantKind::Plain,
+        VariantKind::CLike(n) => VariantKind::CLike(n),
+        VariantKind::Tuple(t) => VariantKind::Tuple(folder.fold_ty(t)),
+        VariantKind::Struct(mem) => VariantKind::Struct(
+            mem.into_iter()
+                .map(|m| folder.fold_struct_member(m))
+                .collect(),
+        ),
+    }
+}
+
+#[inline]
+/// Folds an [ImplKind] in the default way
+pub fn or_fold_impl_kind<F: Fold + ?Sized>(folder: &mut F, kind: ImplKind) -> ImplKind {
+    match kind {
+        ImplKind::Type(t) => ImplKind::Type(folder.fold_ty(t)),
+        ImplKind::Trait { impl_trait, for_type } => ImplKind::Trait {
+            impl_trait: folder.fold_path(impl_trait),
+            for_type: Box::new(folder.fold_ty(*for_type)),
+        },
+    }
+}
+
+#[inline]
+/// Folds a [TyKind] in the default way
+pub fn or_fold_ty_kind<F: Fold + ?Sized>(folder: &mut F, kind: TyKind) -> TyKind {
+    match kind {
+        TyKind::Never => TyKind::Never,
+        TyKind::Empty => TyKind::Empty,
+        TyKind::SelfTy => TyKind::SelfTy,
+        TyKind::Path(p) => TyKind::Path(folder.fold_path(p)),
+        TyKind::Tuple(t) => TyKind::Tuple(folder.fold_ty_tuple(t)),
+        TyKind::Ref(t) => TyKind::Ref(folder.fold_ty_ref(t)),
+        TyKind::Fn(t) => TyKind::Fn(folder.fold_ty_fn(t)),
+    }
+}
+
+#[inline]
+/// Folds a [StmtKind] in the default way
+pub fn or_fold_stmt_kind<F: Fold + ?Sized>(folder: &mut F, kind: StmtKind) -> StmtKind {
+    match kind {
+        StmtKind::Empty => StmtKind::Empty,
+        StmtKind::Local(l) => StmtKind::Local(folder.fold_let(l)),
+        StmtKind::Item(i) => StmtKind::Item(Box::new(folder.fold_item(*i))),
+        StmtKind::Expr(e) => StmtKind::Expr(Box::new(folder.fold_expr(*e))),
+    }
+}
+#[inline]
+/// Folds an [ExprKind] in the default way
+pub fn or_fold_expr_kind<F: Fold + ?Sized>(folder: &mut F, kind: ExprKind) -> ExprKind {
+    match kind {
+        ExprKind::Empty => ExprKind::Empty,
+        ExprKind::Assign(a) => ExprKind::Assign(folder.fold_assign(a)),
+        ExprKind::Binary(b) => ExprKind::Binary(folder.fold_binary(b)),
+        ExprKind::Unary(u) => ExprKind::Unary(folder.fold_unary(u)),
+        ExprKind::Index(i) => ExprKind::Index(folder.fold_index(i)),
+        ExprKind::Path(p) => ExprKind::Path(folder.fold_path(p)),
+        ExprKind::Literal(l) => ExprKind::Literal(folder.fold_literal(l)),
+        ExprKind::Array(a) => ExprKind::Array(folder.fold_array(a)),
+        ExprKind::ArrayRep(a) => ExprKind::ArrayRep(folder.fold_array_rep(a)),
+        ExprKind::AddrOf(a) => ExprKind::AddrOf(folder.fold_addrof(a)),
+        ExprKind::Block(b) => ExprKind::Block(folder.fold_block(b)),
+        ExprKind::Group(g) => ExprKind::Group(folder.fold_group(g)),
+        ExprKind::Tuple(t) => ExprKind::Tuple(folder.fold_tuple(t)),
+        ExprKind::Loop(l) => ExprKind::Loop(folder.fold_loop(l)),
+        ExprKind::While(w) => ExprKind::While(folder.fold_while(w)),
+        ExprKind::If(i) => ExprKind::If(folder.fold_if(i)),
+        ExprKind::For(f) => ExprKind::For(folder.fold_for(f)),
+        ExprKind::Break(b) => ExprKind::Break(folder.fold_break(b)),
+        ExprKind::Return(r) => ExprKind::Return(folder.fold_return(r)),
+        ExprKind::Continue(c) => ExprKind::Continue(folder.fold_continue(c)),
+    }
+}

cl-ast/src/ast_visitor/visit.rs

@@ -0,0 +1,411 @@
+//! A [visitor](Visit) (implementer of the [Visit] trait) walks the immutable AST, mutating itself.
+
+use crate::ast::*;
+use cl_structures::span::Span;
+
+/// Immutably walks the entire AST
+///
+/// Each method acts as a customization point.
+///
+/// There are a set of default implementations for enums
+/// under the name [`or_visit_`*](or_visit_expr_kind),
+/// provided for ease of use.
+///
+/// For all other nodes, traversal is *explicit*.
+pub trait Visit<'a>: Sized {
+    fn visit_span(&mut self, _extents: &'a Span) {}
+    fn visit_mutability(&mut self, _mutable: &'a Mutability) {}
+    fn visit_visibility(&mut self, _vis: &'a Visibility) {}
+    fn visit_identifier(&mut self, _name: &'a Identifier) {}
+    fn visit_literal(&mut self, l: &'a Literal) {
+        or_visit_literal(self, l)
+    }
+    fn visit_bool(&mut self, _b: &'a bool) {}
+    fn visit_char(&mut self, _c: &'a char) {}
+    fn visit_int(&mut self, _i: &'a u128) {}
+    fn visit_string(&mut self, _s: &'a str) {}
+    fn visit_file(&mut self, f: &'a File) {
+        let File { items } = f;
+        items.iter().for_each(|i| self.visit_item(i));
+    }
+    fn visit_attrs(&mut self, a: &'a Attrs) {
+        let Attrs { meta } = a;
+        meta.iter().for_each(|m| self.visit_meta(m));
+    }
+    fn visit_meta(&mut self, m: &'a Meta) {
+        let Meta { name, kind } = m;
+        self.visit_identifier(name);
+        self.visit_meta_kind(kind);
+    }
+    fn visit_meta_kind(&mut self, kind: &'a MetaKind) {
+        or_visit_meta_kind(self, kind)
+    }
+    fn visit_item(&mut self, i: &'a Item) {
+        let Item { extents, attrs, vis, kind } = i;
+        self.visit_span(extents);
+        self.visit_attrs(attrs);
+        self.visit_visibility(vis);
+        self.visit_item_kind(kind);
+    }
+    fn visit_item_kind(&mut self, kind: &'a ItemKind) {
+        or_visit_item_kind(self, kind)
+    }
+    fn visit_alias(&mut self, a: &'a Alias) {
+        let Alias { to, from } = a;
+        self.visit_identifier(to);
+        if let Some(t) = from {
+            self.visit_ty(t)
+        }
+    }
+    fn visit_const(&mut self, c: &'a Const) {
+        let Const { name, ty, init } = c;
+        self.visit_identifier(name);
+        self.visit_ty(ty);
+        self.visit_expr(init);
+    }
+    fn visit_static(&mut self, s: &'a Static) {
+        let Static { mutable, name, ty, init } = s;
+        self.visit_mutability(mutable);
+        self.visit_identifier(name);
+        self.visit_ty(ty);
+        self.visit_expr(init);
+    }
+    fn visit_module(&mut self, m: &'a Module) {
+        let Module { name, kind } = m;
+        self.visit_identifier(name);
+        self.visit_module_kind(kind);
+    }
+    fn visit_module_kind(&mut self, kind: &'a ModuleKind) {
+        or_visit_module_kind(self, kind)
+    }
+    fn visit_function(&mut self, f: &'a Function) {
+        let Function { name, sign, bind, body } = f;
+        self.visit_identifier(name);
+        self.visit_ty_fn(sign);
+        bind.iter().for_each(|p| self.visit_param(p));
+        if let Some(b) = body {
+            self.visit_block(b)
+        }
+    }
+    fn visit_param(&mut self, p: &'a Param) {
+        let Param { mutability, name } = p;
+        self.visit_mutability(mutability);
+        self.visit_identifier(name);
+    }
+    fn visit_struct(&mut self, s: &'a Struct) {
+        let Struct { name, kind } = s;
+        self.visit_identifier(name);
+        self.visit_struct_kind(kind);
+    }
+    fn visit_struct_kind(&mut self, kind: &'a StructKind) {
+        or_visit_struct_kind(self, kind)
+    }
+    fn visit_struct_member(&mut self, m: &'a StructMember) {
+        let StructMember { vis, name, ty } = m;
+        self.visit_visibility(vis);
+        self.visit_identifier(name);
+        self.visit_ty(ty);
+    }
+    fn visit_enum(&mut self, e: &'a Enum) {
+        let Enum { name, kind } = e;
+        self.visit_identifier(name);
+        self.visit_enum_kind(kind);
+    }
+    fn visit_enum_kind(&mut self, kind: &'a EnumKind) {
+        or_visit_enum_kind(self, kind)
+    }
+    fn visit_variant(&mut self, v: &'a Variant) {
+        let Variant { name, kind } = v;
+        self.visit_identifier(name);
+        self.visit_variant_kind(kind);
+    }
+    fn visit_variant_kind(&mut self, kind: &'a VariantKind) {
+        or_visit_variant_kind(self, kind)
+    }
+    fn visit_impl(&mut self, i: &'a Impl) {
+        let Impl { target, body } = i;
+        self.visit_impl_kind(target);
+        self.visit_file(body)
+    }
+    fn visit_impl_kind(&mut self, target: &'a ImplKind) {
+        or_visit_impl_kind(self, target)
+    }
+    fn visit_ty(&mut self, t: &'a Ty) {
+        let Ty { extents, kind } = t;
+        self.visit_span(extents);
+        self.visit_ty_kind(kind);
+    }
+    fn visit_ty_kind(&mut self, kind: &'a TyKind) {
+        or_visit_ty_kind(self, kind)
+    }
+    fn visit_ty_tuple(&mut self, t: &'a TyTuple) {
+        let TyTuple { types } = t;
+        types.iter().for_each(|kind| self.visit_ty_kind(kind))
+    }
+    fn visit_ty_ref(&mut self, t: &'a TyRef) {
+        let TyRef { mutable, count: _, to } = t;
+        self.visit_mutability(mutable);
+        self.visit_path(to);
+    }
+    fn visit_ty_fn(&mut self, t: &'a TyFn) {
+        let TyFn { args, rety } = t;
+        self.visit_ty_kind(args);
+        if let Some(rety) = rety {
+            self.visit_ty(rety);
+        }
+    }
+    fn visit_path(&mut self, p: &'a Path) {
+        let Path { absolute: _, parts } = p;
+        parts.iter().for_each(|p| self.visit_path_part(p))
+    }
+    fn visit_path_part(&mut self, p: &'a PathPart) {
+        match p {
+            PathPart::SuperKw => {}
+            PathPart::SelfKw => {}
+            PathPart::Ident(i) => self.visit_identifier(i),
+        }
+    }
+    fn visit_stmt(&mut self, s: &'a Stmt) {
+        let Stmt { extents, kind, semi } = s;
+        self.visit_span(extents);
+        self.visit_stmt_kind(kind);
+        self.visit_semi(semi);
+    }
+    fn visit_stmt_kind(&mut self, kind: &'a StmtKind) {
+        or_visit_stmt_kind(self, kind)
+    }
+    fn visit_semi(&mut self, _s: &'a Semi) {}
+    fn visit_let(&mut self, l: &'a Let) {
+        let Let { mutable, name, ty, init } = l;
+        self.visit_mutability(mutable);
+        self.visit_identifier(name);
+        if let Some(ty) = ty {
+            self.visit_ty(ty);
+        }
+        if let Some(init) = init {
+            self.visit_expr(init)
+        }
+    }
+    fn visit_expr(&mut self, e: &'a Expr) {
+        let Expr { extents, kind } = e;
+        self.visit_span(extents);
+        self.visit_expr_kind(kind)
+    }
+    fn visit_expr_kind(&mut self, e: &'a ExprKind) {
+        or_visit_expr_kind(self, e)
+    }
+    fn visit_assign(&mut self, a: &'a Assign) {
+        let Assign { kind, parts } = a;
+        let (head, tail) = parts.as_ref();
+        self.visit_assign_kind(kind);
+        self.visit_expr_kind(head);
+        self.visit_expr_kind(tail);
+    }
+    fn visit_assign_kind(&mut self, _kind: &'a AssignKind) {}
+    fn visit_binary(&mut self, b: &'a Binary) {
+        let Binary { kind, parts } = b;
+        let (head, tail) = parts.as_ref();
+        self.visit_binary_kind(kind);
+        self.visit_expr_kind(head);
+        self.visit_expr_kind(tail);
+    }
+    fn visit_binary_kind(&mut self, _kind: &'a BinaryKind) {}
+    fn visit_unary(&mut self, u: &'a Unary) {
+        let Unary { kind, tail } = u;
+        self.visit_unary_kind(kind);
+        self.visit_expr_kind(tail);
+    }
+    fn visit_unary_kind(&mut self, _kind: &'a UnaryKind) {}
+    fn visit_index(&mut self, i: &'a Index) {
+        let Index { head, indices } = i;
+        self.visit_expr_kind(head);
+        indices.iter().for_each(|e| self.visit_expr(e));
+    }
+    fn visit_array(&mut self, a: &'a Array) {
+        let Array { values } = a;
+        values.iter().for_each(|e| self.visit_expr(e))
+    }
+    fn visit_array_rep(&mut self, a: &'a ArrayRep) {
+        let ArrayRep { value, repeat } = a;
+        self.visit_expr_kind(value);
+        self.visit_expr_kind(repeat);
+    }
+    fn visit_addrof(&mut self, a: &'a AddrOf) {
+        let AddrOf { count: _, mutable, expr } = a;
+        self.visit_mutability(mutable);
+        self.visit_expr_kind(expr);
+    }
+    fn visit_block(&mut self, b: &'a Block) {
+        let Block { stmts } = b;
+        stmts.iter().for_each(|s| self.visit_stmt(s));
+    }
+    fn visit_group(&mut self, g: &'a Group) {
+        let Group { expr } = g;
+        self.visit_expr_kind(expr)
+    }
+    fn visit_tuple(&mut self, t: &'a Tuple) {
+        let Tuple { exprs } = t;
+        exprs.iter().for_each(|e| self.visit_expr(e))
+    }
+    fn visit_loop(&mut self, l: &'a Loop) {
+        let Loop { body } = l;
+        self.visit_expr(body)
+    }
+    fn visit_while(&mut self, w: &'a While) {
+        let While { cond, pass, fail } = w;
+        self.visit_expr(cond);
+        self.visit_block(pass);
+        self.visit_else(fail);
+    }
+    fn visit_if(&mut self, i: &'a If) {
+        let If { cond, pass, fail } = i;
+        self.visit_expr(cond);
+        self.visit_block(pass);
+        self.visit_else(fail);
+    }
+    fn visit_for(&mut self, f: &'a For) {
+        let For { bind, cond, pass, fail } = f;
+        self.visit_identifier(bind);
+        self.visit_expr(cond);
+        self.visit_block(pass);
+        self.visit_else(fail);
+    }
+    fn visit_else(&mut self, e: &'a Else) {
+        let Else { body } = e;
+        if let Some(body) = body {
+            self.visit_expr(body)
+        }
+    }
+    fn visit_break(&mut self, b: &'a Break) {
+        let Break { body } = b;
+        if let Some(body) = body {
+            self.visit_expr(body)
+        }
+    }
+    fn visit_return(&mut self, r: &'a Return) {
+        let Return { body } = r;
+        if let Some(body) = body {
+            self.visit_expr(body)
+        }
+    }
+    fn visit_continue(&mut self, c: &'a Continue) {
+        let Continue = c;
+    }
+}
+
+pub fn or_visit_literal<'a, V: Visit<'a>>(visitor: &mut V, l: &'a Literal) {
+    match l {
+        Literal::Bool(b) => visitor.visit_bool(b),
+        Literal::Char(c) => visitor.visit_char(c),
+        Literal::Int(i) => visitor.visit_int(i),
+        Literal::String(s) => visitor.visit_string(s),
+    }
+}
+
+pub fn or_visit_meta_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a MetaKind) {
+    match kind {
+        MetaKind::Plain => {}
+        MetaKind::Equals(l) => visitor.visit_literal(l),
+        MetaKind::Func(lits) => lits.iter().for_each(|l| visitor.visit_literal(l)),
+    }
+}
+
+pub fn or_visit_item_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a ItemKind) {
+    match kind {
+        ItemKind::Module(m) => visitor.visit_module(m),
+        ItemKind::Alias(a) => visitor.visit_alias(a),
+        ItemKind::Enum(e) => visitor.visit_enum(e),
+        ItemKind::Struct(s) => visitor.visit_struct(s),
+        ItemKind::Const(c) => visitor.visit_const(c),
+        ItemKind::Static(s) => visitor.visit_static(s),
+        ItemKind::Function(f) => visitor.visit_function(f),
+        ItemKind::Impl(i) => visitor.visit_impl(i),
+    }
+}
+
+pub fn or_visit_module_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a ModuleKind) {
+    match kind {
+        ModuleKind::Inline(f) => visitor.visit_file(f),
+        ModuleKind::Outline => {}
+    }
+}
+
+pub fn or_visit_struct_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a StructKind) {
+    match kind {
+        StructKind::Empty => {}
+        StructKind::Tuple(ty) => ty.iter().for_each(|t| visitor.visit_ty(t)),
+        StructKind::Struct(m) => m.iter().for_each(|m| visitor.visit_struct_member(m)),
+    }
+}
+
+pub fn or_visit_enum_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a EnumKind) {
+    match kind {
+        EnumKind::NoVariants => {}
+        EnumKind::Variants(variants) => variants.iter().for_each(|v| visitor.visit_variant(v)),
+    }
+}
+
+pub fn or_visit_variant_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a VariantKind) {
+    match kind {
+        VariantKind::Plain => {}
+        VariantKind::CLike(_) => {}
+        VariantKind::Tuple(t) => visitor.visit_ty(t),
+        VariantKind::Struct(m) => m.iter().for_each(|m| visitor.visit_struct_member(m)),
+    }
+}
+
+pub fn or_visit_impl_kind<'a, V: Visit<'a>>(visitor: &mut V, target: &'a ImplKind) {
+    match target {
+        ImplKind::Type(t) => visitor.visit_ty(t),
+        ImplKind::Trait { impl_trait, for_type } => {
+            visitor.visit_path(impl_trait);
+            visitor.visit_ty(for_type)
+        }
+    }
+}
+
+pub fn or_visit_ty_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a TyKind) {
+    match kind {
+        TyKind::Never => {}
+        TyKind::Empty => {}
+        TyKind::SelfTy => {}
+        TyKind::Path(p) => visitor.visit_path(p),
+        TyKind::Tuple(t) => visitor.visit_ty_tuple(t),
+        TyKind::Ref(t) => visitor.visit_ty_ref(t),
+        TyKind::Fn(t) => visitor.visit_ty_fn(t),
+    }
+}
+
+pub fn or_visit_stmt_kind<'a, V: Visit<'a>>(visitor: &mut V, kind: &'a StmtKind) {
+    match kind {
+        StmtKind::Empty => {}
+        StmtKind::Local(l) => visitor.visit_let(l),
+        StmtKind::Item(i) => visitor.visit_item(i),
+        StmtKind::Expr(e) => visitor.visit_expr(e),
+    }
+}
+
+pub fn or_visit_expr_kind<'a, V: Visit<'a>>(visitor: &mut V, e: &'a ExprKind) {
+    match e {
+        ExprKind::Empty => {}
+        ExprKind::Assign(a) => visitor.visit_assign(a),
+        ExprKind::Binary(b) => visitor.visit_binary(b),
+        ExprKind::Unary(u) => visitor.visit_unary(u),
+        ExprKind::Index(i) => visitor.visit_index(i),
+        ExprKind::Path(p) => visitor.visit_path(p),
+        ExprKind::Literal(l) => visitor.visit_literal(l),
+        ExprKind::Array(a) => visitor.visit_array(a),
+        ExprKind::ArrayRep(a) => visitor.visit_array_rep(a),
+        ExprKind::AddrOf(a) => visitor.visit_addrof(a),
+        ExprKind::Block(b) => visitor.visit_block(b),
+        ExprKind::Group(g) => visitor.visit_group(g),
+        ExprKind::Tuple(t) => visitor.visit_tuple(t),
+        ExprKind::Loop(l) => visitor.visit_loop(l),
+        ExprKind::While(w) => visitor.visit_while(w),
+        ExprKind::If(i) => visitor.visit_if(i),
+        ExprKind::For(f) => visitor.visit_for(f),
+        ExprKind::Break(b) => visitor.visit_break(b),
+        ExprKind::Return(r) => visitor.visit_return(r),
+        ExprKind::Continue(c) => visitor.visit_continue(c),
+    }
+}

cl-ast/src/desugar.rs

@@ -0,0 +1,5 @@
+//! Desugaring passes for Conlang
+
+pub mod while_else;
+
+pub mod squash_groups;

cl-ast/src/desugar/squash_groups.rs

@@ -0,0 +1,14 @@
+//! Squashes group expressions
+use crate::{ast::*, ast_visitor::fold::*};
+
+/// Squashes group expressions
+pub struct SquashGroups;
+
+impl Fold for SquashGroups {
+    fn fold_expr_kind(&mut self, kind: ExprKind) -> ExprKind {
+        match kind {
+            ExprKind::Group(Group { expr }) => self.fold_expr_kind(*expr),
+            _ => or_fold_expr_kind(self, kind),
+        }
+    }
+}

cl-ast/src/desugar/while_else.rs

@@ -0,0 +1,34 @@
+//! Desugars `while {...} else` expressions
+//! into `loop if {...} else break` expressions
+
+use crate::{ast::*, ast_visitor::fold::Fold};
+use cl_structures::span::Span;
+
+/// Desugars while-else expressions
+/// into loop-if-else-break expressions
+pub struct WhileElseDesugar;
+
+impl Fold for WhileElseDesugar {
+    fn fold_expr(&mut self, e: Expr) -> Expr {
+        let Expr { extents, kind } = e;
+        let kind = desugar_while(extents, kind);
+        Expr { extents: self.fold_span(extents), kind: self.fold_expr_kind(kind) }
+    }
+}
+
+/// Desugars while(-else) expressions into loop-if-else-break expressions
+fn desugar_while(extents: Span, kind: ExprKind) -> ExprKind {
+    match kind {
+        // work backwards: fail -> break -> if -> loop
+        ExprKind::While(While { cond, pass, fail: Else { body } }) => {
+            // Preserve the else-expression's extents, if present, or use the parent's extents
+            let fail_span = body.as_ref().map(|body| body.extents).unwrap_or(extents);
+            let break_expr = Expr { extents: fail_span, kind: ExprKind::Break(Break { body }) };
+
+            let loop_body = If { cond, pass, fail: Else { body: Some(Box::new(break_expr)) } };
+            let loop_body = Expr { extents, kind: ExprKind::If(loop_body) };
+            ExprKind::Loop(Loop { body: Box::new(loop_body) })
+        }
+        _ => kind,
+    }
+}

cl-ast/src/lib.rs

@@ -16,4 +16,6 @@ pub use ast::*;
 
 pub mod ast;
 pub mod ast_impl;
+pub mod ast_visitor;
+pub mod desugar;
 pub mod format;

cl-repl/examples/typeck.rs

@@ -1,3 +1,7 @@
+use cl_ast::{
+    ast_visitor::fold::Fold,
+    desugar::{squash_groups::SquashGroups, while_else::WhileElseDesugar},
+};
 use cl_lexer::Lexer;
 use cl_parser::Parser;
 use cl_repl::repline::{error::Error as RlError, Repline};
@@ -33,6 +37,7 @@ fn main() -> Result<(), Box<dyn Error>> {
             Err(e)?
         }
     };
+
     unsafe { TREES.push(code) }.collect_in_root(&mut prj)?;
 
     main_menu(&mut prj)
@@ -81,6 +86,7 @@ fn main_menu(prj: &mut Project) -> Result<(), Box<dyn Error>> {
             "l" | "list" => list_types(prj),
             "q" | "query" => query_type_expression(prj),
             "r" | "resolve" => resolve_all(prj),
+            "d" | "desugar" => live_desugar(),
             "h" | "help" => {
                 println!(
                     "Valid commands are:
@@ -88,6 +94,7 @@ fn main_menu(prj: &mut Project) -> Result<(), Box<dyn Error>> {
     list    (l): List all known types
     query   (q): Query the type system
     resolve (r): Perform type resolution
+    desugar (d): WIP: Test the experimental desugaring passes
     help    (h): Print this list
     exit    (e): Exit the program"
                 );
@@ -105,7 +112,7 @@ fn enter_code(prj: &mut Project) -> Result<(), Box<dyn Error>> {
             return Ok(Response::Break);
         }
         let code = Parser::new(Lexer::new(line)).file()?;
-
+        let code = WhileElseDesugar.fold_file(code);
         // Safety: this is totally unsafe
         unsafe { TREES.push(code) }.collect_in_root(prj)?;
 
@@ -113,6 +120,21 @@ fn enter_code(prj: &mut Project) -> Result<(), Box<dyn Error>> {
     })
 }
 
+fn live_desugar() -> Result<(), Box<dyn Error>> {
+    read_and(C_RESV, "se>", |line| {
+        let code = Parser::new(Lexer::new(line)).stmt()?;
+        println!("Raw, as parsed:\n{C_LISTING}{code}\x1b[0m");
+
+        let code = SquashGroups.fold_stmt(code);
+        println!("SquashGroups\n{C_LISTING}{code}\x1b[0m");
+
+        let code = WhileElseDesugar.fold_stmt(code);
+        println!("WhileElseDesugar\n{C_LISTING}{code}\x1b[0m");
+
+        Ok(Response::Accept)
+    })
+}
+
 fn query_type_expression(prj: &mut Project) -> Result<(), Box<dyn Error>> {
     read_and(C_RESV, "ty>", |line| {
         if line.trim().is_empty() {

cl-repl/src/lib.rs

@@ -112,10 +112,16 @@ pub mod program {
             self.parse_file().or_else(|_| self.parse_stmt())
         }
         pub fn parse_stmt(&self) -> PResult<Program<'t, Parsed>> {
-            Ok(Program { data: Parsed::Stmt(Parser::new(self.lex()).stmt()?), text: self.text })
+            let stmt = Parser::new(self.lex()).stmt()?;
+            // let stmt = WhileElseDesugar.fold_stmt(stmt);
+
+            Ok(Program { data: Parsed::Stmt(stmt), text: self.text })
         }
         pub fn parse_file(&self) -> PResult<Program<'t, Parsed>> {
-            Ok(Program { data: Parsed::File(Parser::new(self.lex()).file()?), text: self.text })
+            let file = Parser::new(self.lex()).file()?;
+            // let file = WhileElseDesugar.fold_file(file);
+
+            Ok(Program { data: Parsed::File(file), text: self.text })
         }
     }