diff --git a/src/ast.ts b/src/ast.ts
index 500ffbe..85c5ce2 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -3,32 +3,53 @@ import { LitIntType } from "./lexer";
 
 export type Ast<P extends Phase> = {
   rootItems: Item<P>[];
-  typeckResults?: TypeckResults;
   itemsById: Map<ItemId, Item<P>>;
   packageName: string;
-};
+} & P["typeckResults"];
 
 export type Phase = {
   res: unknown;
+  defPath: unknown;
+  ty: unknown;
+  typeckResults: unknown;
 };
 
-type NoRes = object;
+type No = object;
+
 type HasRes = { res: Resolution };
+type HasDefPath = { defPath: string[] };
+type HasTy = { ty: Ty };
+type HasTypeckResults = { typeckResults: TypeckResults };
 
 export type Parsed = {
-  res: NoRes;
+  res: No;
+  defPath: No;
+  ty: No;
+  typeckResults: No;
 };
 export type Built = {
-  res: NoRes;
+  res: No;
+  defPath: No;
+  ty: No;
+  typeckResults: No;
 };
 export type Resolved = {
   res: HasRes;
+  defPath: HasDefPath;
+  ty: No;
+  typeckResults: No;
 };
 export type Typecked = {
   res: HasRes;
+  defPath: HasDefPath;
+  ty: HasTy;
+  typeckResults: HasTypeckResults;
 };
 export type AnyPhase = {
-  res: NoRes | HasRes;
+  res: No | HasRes;
+  defPath: No | HasDefPath;
+  ty: No | HasTy;
+  typeckResults: No | HasTypeckResults;
 };
 
 export type Ident = {
@@ -64,8 +85,7 @@ export type ItemKind<P extends Phase> =
 export type Item<P extends Phase> = ItemKind<P> & {
   span: Span;
   id: ItemId;
-  defPath?: string[];
-};
+} & P["defPath"];
 
 export type FunctionDef<P extends Phase> = {
   name: string;
@@ -246,8 +266,7 @@ export type ExprKind<P extends Phase> =
 
 export type Expr<P extends Phase> = ExprKind<P> & {
   span: Span;
-  ty?: Ty;
-};
+} & P["ty"];
 
 export type StringLiteral = {
   kind: "str";
@@ -335,7 +354,6 @@ export type TypeKind<P extends Phase> =
 
 export type Type<P extends Phase> = TypeKind<P> & {
   span: Span;
-  ty?: Ty;
 };
 
 // name resolution stuff
@@ -526,7 +544,7 @@ export function foldAst<From extends Phase, To extends Phase>(
   return {
     rootItems: ast.rootItems.map((item) => folder.item(item)),
     itemsById: folder.newItemsById,
-    typeckResults: ast.typeckResults,
+    typeckResults: "typeckResults" in ast ? ast.typeckResults : undefined,
     packageName: ast.packageName,
   };
 }
diff --git a/src/lower.ts b/src/lower.ts
index f207c6e..1398ba8 100644
--- a/src/lower.ts
+++ b/src/lower.ts
@@ -231,7 +231,7 @@ function lowerFunc(
   const type = internFuncType(cx, wasmType);
 
   const wasmFunc: wasm.Func = {
-    _name: mangleDefPath(item.defPath!),
+    _name: mangleDefPath(item.defPath),
     type,
     locals: [],
     body: [],
@@ -269,7 +269,7 @@ function lowerExpr(
   instrs: wasm.Instr[],
   expr: Expr<Typecked>
 ) {
-  const ty = expr.ty!;
+  const ty = expr.ty;
 
   exprKind: switch (expr.kind) {
     case "empty": {
@@ -278,7 +278,7 @@ function lowerExpr(
     }
     case "let": {
       lowerExpr(fcx, instrs, expr.rhs);
-      const types = wasmTypeForBody(expr.rhs.ty!);
+      const types = wasmTypeForBody(expr.rhs.ty);
 
       const local = fcx.wasm.locals.length + fcx.wasmType.params.length;
 
@@ -333,7 +333,7 @@ function lowerExpr(
         const instr: wasm.Instr = {
           kind: "block",
           instrs: lowerExprBlockBody(fcx, expr),
-          type: blockTypeForBody(fcx.cx, expr.ty!),
+          type: blockTypeForBody(fcx.cx, expr.ty),
         };
 
         instrs.push(instr);
@@ -404,8 +404,8 @@ function lowerExpr(
       lowerExpr(fcx, instrs, expr.lhs);
       lowerExpr(fcx, instrs, expr.rhs);
 
-      const lhsTy = expr.lhs.ty!;
-      const rhsTy = expr.rhs.ty!;
+      const lhsTy = expr.lhs.ty;
+      const rhsTy = expr.rhs.ty;
       if (
         (lhsTy.kind === "int" && rhsTy.kind === "int") ||
         (lhsTy.kind === "i32" && rhsTy.kind === "i32")
@@ -592,11 +592,11 @@ function lowerExpr(
 
       lowerExpr(fcx, instrs, expr.lhs);
 
-      switch (expr.lhs.ty!.kind) {
+      switch (expr.lhs.ty.kind) {
         case "tuple": {
           // Tuples have a by-value ABI, so we can simply index.
           const lhsSize = argRetAbi(expr.lhs.ty).length;
-          const resultAbi = argRetAbi(expr.ty!);
+          const resultAbi = argRetAbi(expr.ty);
           const resultSize = resultAbi.length;
           const wasmIdx = wasmTypeIdxForTupleField(
             expr.lhs.ty,
@@ -655,7 +655,7 @@ function lowerExpr(
         kind: "if",
         then: thenInstrs,
         else: elseInstrs,
-        type: blockTypeForBody(fcx.cx, expr.ty!),
+        type: blockTypeForBody(fcx.cx, expr.ty),
       });
 
       break;
@@ -669,7 +669,7 @@ function lowerExpr(
       lowerExpr(fcx, bodyInstrs, expr.body);
 
       // For diverging bodies, we don't need to bother creating the back edge.
-      if (expr.body.ty!.kind !== "never") {
+      if (expr.body.ty.kind !== "never") {
         bodyInstrs.push({
           kind: "br",
           label: /*innermost control structure, the loop*/ 0,
@@ -680,13 +680,13 @@ function lowerExpr(
       outerBlockInstrs.push({
         kind: "loop",
         instrs: bodyInstrs,
-        type: blockTypeForBody(fcx.cx, expr.ty!),
+        type: blockTypeForBody(fcx.cx, expr.ty),
       });
 
       instrs.push({
         kind: "block",
         instrs: outerBlockInstrs,
-        type: blockTypeForBody(fcx.cx, expr.ty!),
+        type: blockTypeForBody(fcx.cx, expr.ty),
       });
       fcx.loopDepths.delete(expr.loopId);
 
@@ -695,8 +695,6 @@ function lowerExpr(
     case "break": {
       const loopDepth = unwrap(fcx.loopDepths.get(expr.target!));
 
-      console.log(loopDepth, fcx.currentBlockDepth);
-
       instrs.push({
         kind: "br",
         label: fcx.currentBlockDepth - loopDepth - 1,
@@ -733,11 +731,11 @@ function lowerExprBlockBody(
 
   for (const inner of headExprs) {
     lowerExpr(fcx, innerInstrs, inner);
-    if (inner.ty!.kind === "never") {
+    if (inner.ty.kind === "never") {
       // The rest of the block is unreachable, so we don't bother codegening it.
       break;
     }
-    const types = wasmTypeForBody(inner.ty!);
+    const types = wasmTypeForBody(inner.ty);
     types.forEach(() => innerInstrs.push({ kind: "drop" }));
   }
 
@@ -872,7 +870,7 @@ function addRt(cx: Context, ast: Ast<Typecked>) {
   cx.relocations.push({
     kind: "funccall",
     instr: mainCall,
-    res: ast.typeckResults!.main,
+    res: ast.typeckResults.main,
   });
 
   const start: wasm.Func = {
diff --git a/src/typeck.ts b/src/typeck.ts
index 7970f1f..703a941 100644
--- a/src/typeck.ts
+++ b/src/typeck.ts
@@ -341,7 +341,7 @@ export function typeck(ast: Ast<Resolved>): Ast<Typecked> {
     if (item.kind === "function" && item.node.name === "main") {
       const func = item.node;
       if (func.returnType !== undefined) {
-        const ty = func.returnType.ty!;
+        const ty = func.body.ty;
         if (ty.kind !== "tuple" || ty.elems.length !== 0) {
           throw new CompilerError(
             `\`main\` has an invalid signature. main takes no arguments and returns nothing`,
@@ -586,7 +586,7 @@ export function checkBody(
             : infcx.newVar();
 
           const rhs = this.expr(expr.rhs);
-          infcx.assign(bindingTy, rhs.ty!, expr.span);
+          infcx.assign(bindingTy, rhs.ty, expr.span);
 
           // AST validation ensures that lets can only be in blocks, where
           // the types will be popped.
@@ -596,7 +596,6 @@ export function checkBody(
 
           const type: Type<Typecked> | undefined = loweredBindingTy && {
             ...expr.type!,
-            ty: loweredBindingTy,
           };
 
           return {
@@ -612,7 +611,7 @@ export function checkBody(
           const lhs = this.expr(expr.lhs);
           const rhs = this.expr(expr.rhs);
 
-          infcx.assign(lhs.ty!, rhs.ty!, expr.span);
+          infcx.assign(lhs.ty, rhs.ty, expr.span);
 
           switch (lhs.kind) {
             case "ident":
@@ -641,7 +640,7 @@ export function checkBody(
 
           const exprs = expr.exprs.map((expr) => this.expr(expr));
 
-          const ty = exprs.length > 0 ? exprs[exprs.length - 1].ty! : TY_UNIT;
+          const ty = exprs.length > 0 ? exprs[exprs.length - 1].ty : TY_UNIT;
 
           localTys.length = prevLocalTysLen;
 
@@ -686,19 +685,19 @@ export function checkBody(
           const lhs = this.expr(expr.lhs);
           const rhs = this.expr(expr.rhs);
 
-          lhs.ty = infcx.resolveIfPossible(lhs.ty!);
-          rhs.ty = infcx.resolveIfPossible(rhs.ty!);
+          lhs.ty = infcx.resolveIfPossible(lhs.ty);
+          rhs.ty = infcx.resolveIfPossible(rhs.ty);
 
-          return checkBinary({ ...expr, lhs, rhs });
+          return checkBinary(expr, lhs, rhs);
         }
         case "unary": {
           const rhs = this.expr(expr.rhs);
-          rhs.ty = infcx.resolveIfPossible(rhs.ty!);
-          return checkUnary({ ...expr, rhs });
+          rhs.ty = infcx.resolveIfPossible(rhs.ty);
+          return checkUnary(expr, rhs);
         }
         case "call": {
           const lhs = this.expr(expr.lhs);
-          lhs.ty = infcx.resolveIfPossible(lhs.ty!);
+          lhs.ty = infcx.resolveIfPossible(lhs.ty);
           const lhsTy = lhs.ty;
           if (lhsTy.kind !== "fn") {
             throw new CompilerError(
@@ -718,7 +717,7 @@ export function checkBody(
             }
             const arg = checker.expr(args[i]);
 
-            infcx.assign(param, arg.ty!, args[i].span);
+            infcx.assign(param, arg.ty, args[i].span);
           });
 
           if (args.length > lhsTy.params.length) {
@@ -732,7 +731,7 @@ export function checkBody(
         }
         case "fieldAccess": {
           const lhs = this.expr(expr.lhs);
-          lhs.ty = infcx.resolveIfPossible(lhs.ty!);
+          lhs.ty = infcx.resolveIfPossible(lhs.ty);
 
           const { field } = expr;
           let ty: Ty;
@@ -807,14 +806,14 @@ export function checkBody(
           const then = this.expr(expr.then);
           const elsePart = expr.else && this.expr(expr.else);
 
-          infcx.assign(TY_BOOL, cond.ty!, cond.span);
+          infcx.assign(TY_BOOL, cond.ty, cond.span);
 
           let ty: Ty;
           if (elsePart) {
-            infcx.assign(then.ty!, elsePart.ty!, elsePart.span);
+            infcx.assign(then.ty, elsePart.ty, elsePart.span);
             ty = then.ty!;
           } else {
-            infcx.assign(TY_UNIT, then.ty!, then.span);
+            infcx.assign(TY_UNIT, then.ty, then.span);
             ty = TY_UNIT;
           }
 
@@ -827,7 +826,7 @@ export function checkBody(
           });
 
           const body = this.expr(expr.body);
-          infcx.assign(TY_UNIT, body.ty!, body.span);
+          infcx.assign(TY_UNIT, body.ty, body.span);
 
           const hadBreak = loopState.pop();
           const ty = hadBreak ? TY_UNIT : TY_NEVER;
@@ -875,7 +874,7 @@ export function checkBody(
                 name.span
               );
             }
-            infcx.assign(fieldTy[1], field.ty!, field.span);
+            infcx.assign(fieldTy[1], field.ty, field.span);
             assignedFields.add(name.name);
           });
 
@@ -899,7 +898,7 @@ export function checkBody(
 
           const ty: Ty = {
             kind: "tuple",
-            elems: fields.map((field) => field.ty!),
+            elems: fields.map((field) => field.ty),
           };
 
           return { ...expr, fields, ty };
@@ -919,7 +918,7 @@ export function checkBody(
 
   const checked = checker.expr(body);
 
-  infcx.assign(fnTy.returnTy, checked.ty!, body.span);
+  infcx.assign(fnTy.returnTy, checked.ty, body.span);
 
   const resolveTy = (ty: Ty, span: Span) => {
     const resTy = infcx.resolveIfPossible(ty);
@@ -933,7 +932,7 @@ export function checkBody(
   const resolver: Folder<Typecked, Typecked> = {
     ...mkDefaultFolder(),
     expr(expr) {
-      const ty = resolveTy(expr.ty!, expr.span);
+      const ty = resolveTy(expr.ty, expr.span);
 
       if (expr.kind === "block") {
         expr.locals!.forEach((local) => {
@@ -944,8 +943,7 @@ export function checkBody(
       return { ...expr, ty };
     },
     type(type) {
-      const ty = resolveTy(type.ty!, type.span);
-      return { ...type, ty };
+      return type;
     },
     ident(ident) {
       return ident;
@@ -958,58 +956,61 @@ export function checkBody(
 }
 
 function checkBinary(
-  expr: Expr<Typecked> & ExprBinary<Typecked>
+  expr: Expr<Resolved> & ExprBinary<Resolved>,
+  lhs: Expr<Typecked>,
+  rhs: Expr<Typecked>
 ): Expr<Typecked> {
-  const lhsTy = expr.lhs.ty!;
-  const rhsTy = expr.rhs.ty!;
+  const lhsTy = lhs.ty;
+  const rhsTy = rhs.ty;
 
   if (COMPARISON_KINDS.includes(expr.binaryKind)) {
     if (lhsTy.kind === "int" && rhsTy.kind === "int") {
-      return { ...expr, ty: TY_BOOL };
+      return { ...expr, lhs, rhs, ty: TY_BOOL };
     }
 
     if (lhsTy.kind === "string" && rhsTy.kind === "string") {
-      return { ...expr, ty: TY_BOOL };
+      return { ...expr, lhs, rhs, ty: TY_BOOL };
     }
 
     if (EQUALITY_KINDS.includes(expr.binaryKind)) {
       if (lhsTy.kind === "bool" && rhsTy.kind === "bool") {
-        return { ...expr, ty: TY_BOOL };
+        return { ...expr, lhs, rhs, ty: TY_BOOL };
       }
     }
   }
 
   if (lhsTy.kind === "int" && rhsTy.kind === "int") {
-    return { ...expr, ty: TY_INT };
+    return { ...expr, lhs, rhs, ty: TY_INT };
   }
   if (lhsTy.kind === "i32" && rhsTy.kind === "i32") {
-    return { ...expr, ty: TY_I32 };
+    return { ...expr, lhs, rhs, ty: TY_I32 };
   }
 
   if (LOGICAL_KINDS.includes(expr.binaryKind)) {
     if (lhsTy.kind === "bool" && rhsTy.kind === "bool") {
-      return { ...expr, ty: TY_BOOL };
+      return { ...expr, lhs, rhs, ty: TY_BOOL };
     }
   }
 
   throw new CompilerError(
-    `invalid types for binary operation: ${printTy(expr.lhs.ty!)} ${
+    `invalid types for binary operation: ${printTy(lhs.ty)} ${
       expr.binaryKind
-    } ${printTy(expr.rhs.ty!)}`,
+    } ${printTy(rhs.ty)}`,
     expr.span
   );
 }
 
 function checkUnary(
-  expr: Expr<Typecked> & ExprUnary<Typecked>
+  expr: Expr<Resolved> & ExprUnary<Resolved>,
+  rhs: Expr<Typecked>
 ): Expr<Typecked> {
-  const rhsTy = expr.rhs.ty!;
+  const rhsTy = rhs.ty;
 
   if (
     expr.unaryKind === "!" &&
     (rhsTy.kind === "int" || rhsTy.kind === "bool")
   ) {
-    return { ...expr, ty: rhsTy };
+    return { ...expr, rhs, ty: rhsTy };
   }
 
   if (expr.unaryKind === "-" && rhsTy.kind == "int") {
@@ -1017,9 +1018,7 @@ function checkUnary(
   }
 
   throw new CompilerError(
-    `invalid types for unary operation: ${expr.unaryKind} ${printTy(
-      expr.rhs.ty!
-    )}`,
+    `invalid types for unary operation: ${expr.unaryKind} ${printTy(rhs.ty)}`,
     expr.span
   );
 }