diff --git a/src/ast.ts b/src/ast.ts
index 85cbbbb..6253dda 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -54,15 +54,18 @@ export type ExprEmpty = { kind: "empty" };
 
 export type ExprLet = {
   kind: "let";
-  name: string;
+  name: Identifier;
   type?: Type;
   rhs: Expr;
-  after: Expr;
+  // IMPORTANT: This is (sadly) shared with ExprBlock.
+  local?: LocalInfo,
 };
 
 export type ExprBlock = {
   kind: "block";
   exprs: Expr[];
+  // IMPORTANT: This is (sadly) shared with ExprLet.
+  locals?: LocalInfo[];
 };
 
 export type ExprLiteral = {
@@ -206,13 +209,15 @@ export type Type = TypeKind & {
   ty?: Ty;
 };
 
+// name resolution stuff
+
 export type Resolution =
   | {
       kind: "local";
       /**
        * The index of the local variable, from inside out.
        * ```
-       * let a in let b in (a, b);
+       * let a = 0; let b; (a, b);
        *     ^        ^
        *     1        0
        * ```
@@ -246,6 +251,14 @@ export const BUILTINS = [
 
 export type BuiltinName = (typeof BUILTINS)[number];
 
+export type LocalInfo = {
+  name: string;
+  span: Span;
+  ty?: Ty;
+};
+
+// types
+
 export type TyString = {
   kind: "string";
 };
@@ -397,7 +410,6 @@ export function superFoldExpr(expr: Expr, folder: Folder): Expr {
         name: expr.name,
         type: expr.type && folder.type(expr.type),
         rhs: folder.expr(expr.rhs),
-        after: folder.expr(expr.after),
       };
     }
     case "block": {
diff --git a/src/error.ts b/src/error.ts
index 432bf57..fce66b5 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -52,8 +52,13 @@ function renderError(input: string, e: CompilerError) {
   console.error(`${lineIdx} | ${spanToSnippet(input, line)}`);
   const startRelLine =
     e.span.start === Number.MAX_SAFE_INTEGER ? 0 : e.span.start - line.start;
+
+  const spanLength = min(e.span.end, line.end) - e.span.start;
+
   console.error(
-    `${" ".repeat(String(lineIdx).length)}   ${" ".repeat(startRelLine)}^`
+    `${" ".repeat(String(lineIdx).length)}   ${" ".repeat(
+      startRelLine
+    )}${"^".repeat(spanLength)}`
   );
 }
 
@@ -81,3 +86,7 @@ export function lines(input: string): Span[] {
 export function todo(msg: string): never {
   throw new CompilerError(`TODO: ${msg}`, { start: 0, end: 0 });
 }
+
+function min(a: number, b: number): number {
+  return a < b ? a : b;
+}
diff --git a/src/index.ts b/src/index.ts
index c87a943..92b5dc2 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -10,14 +10,13 @@ import fs from "fs";
 import { exec } from "child_process";
 
 const input = `
-type Uwu = (
-  meow: String,
-  oops: Int,
-  aaa: (),
-);
+function printInt(a: Int) = ;
 
-function aa(a: Int, b: Uwu): Uwu = Uwu {meow: "",oops:0,aaa:()};
-function main() = ();
+function main() = (
+  let a = 0;
+  let b = 0;
+  printInt(a + b);
+);
 `;
 
 function main() {
@@ -44,8 +43,8 @@ function main() {
 
     console.log("-----AST typecked------");
     const typecked = typeck(resolved);
-
-    return;
+    console.dir(typecked, {depth: 8});
+    
 
     console.log("-----wasm--------------");
     const wasmModule = lowerToWasm(typecked);
diff --git a/src/lexer.ts b/src/lexer.ts
index a8adbbd..d93d122 100644
--- a/src/lexer.ts
+++ b/src/lexer.ts
@@ -3,7 +3,6 @@ import { CompilerError, Span } from "./error";
 export type DatalessToken =
   | "function"
   | "let"
-  | "in"
   | "if"
   | "then"
   | "else"
@@ -79,6 +78,14 @@ export function tokenize(input: string): Token[] {
     const next = input[i];
     const span: Span = { start: i, end: i + 1 };
 
+    if (next === "/" && input[i + 1] === "/") {
+      while (input[i] !== "\n") {
+        i++;
+      }
+
+      continue;
+    }
+
     if (SINGLE_PUNCT.includes(next)) {
       tokens.push({ kind: next as DatalessToken, span });
     } else {
@@ -207,15 +214,16 @@ function isWhitespace(char: string): boolean {
   return char === " " || char === "\t" || char === "\n" || char === "\r";
 }
 
-const keywords = new Set<string>([
+const KEYOWRDS: DatalessToken[] = [
   "function",
   "let",
-  "in",
   "if",
   "then",
   "else",
   "type",
-]);
+];
+
+const KEYWORD_SET = new Set<string>(KEYOWRDS);
 function isKeyword(kw: string): DatalessToken | undefined {
-  return keywords.has(kw) ? (kw as DatalessToken) : undefined;
+  return KEYWORD_SET.has(kw) ? (kw as DatalessToken) : undefined;
 }
diff --git a/src/lower.ts b/src/lower.ts
index ec9e655..0b76f4f 100644
--- a/src/lower.ts
+++ b/src/lower.ts
@@ -121,6 +121,8 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
     case "block":
       if (expr.exprs.length === 1) {
         lowerExpr(fcx, instrs, expr.exprs[0]);
+      } else {
+        todo("complex blocks");
       }
       break;
     case "literal":
diff --git a/src/parser.ts b/src/parser.ts
index b0ac386..4f501ad 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -4,9 +4,11 @@ import {
   Ast,
   BinaryKind,
   COMPARISON_KINDS,
+  DEFAULT_FOLDER,
   Expr,
   ExprStructLiteral,
   FieldDef,
+  Folder,
   FunctionArg,
   FunctionDef,
   Identifier,
@@ -16,9 +18,11 @@ import {
   TypeDef,
   UNARY_KINDS,
   UnaryKind,
+  foldAst,
+  superFoldExpr,
 } from "./ast";
-import { CompilerError, Span, todo } from "./error";
-import { BaseToken, DatalessToken, Token, TokenIdent } from "./lexer";
+import { CompilerError, Span, spanMerge } from "./error";
+import { BaseToken, Token, TokenIdent } from "./lexer";
 
 type Parser<T> = (t: Token[]) => [Token[], T];
 
@@ -33,7 +37,11 @@ export function parse(t: Token[]): Ast {
 
   const withIds = items.map((item, i) => ({ ...item, id: i }));
 
-  return { items: withIds };
+  const ast = { items: withIds };
+
+  validateAst(ast);
+
+  return ast;
 }
 
 function parseItem(t: Token[]): [Token[], Item] {
@@ -127,7 +135,7 @@ function parseItem(t: Token[]): [Token[], Item] {
 
 function parseExpr(t: Token[]): [Token[], Expr] {
   /*
-  EXPR = { LET | COMPARISON | IF }
+  EXPR = COMPARISON
 
   LET = "let" NAME { ":" TYPE } "=" EXPR "in" EXPR
   IF = "if" EXPR "then" EXPR { "else" EXPR }
@@ -145,56 +153,11 @@ function parseExpr(t: Token[]): [Token[], Expr] {
 
   CALL = ATOM { "(" EXPR_LIST ")" }
 
-  ATOM = "(" { EXPR ";" } EXPR ")" | IDENT { STRUCT_INIT } | LITERAL | EMPTY
+  ATOM = "(" { EXPR ";" } EXPR ")" | IDENT { STRUCT_INIT } | LITERAL | EMPTY | LET | IF
   EMPTY =
   STRUCT_INIT = "{" { NAME ":" EXPR } { "," NAME ":" EXPR } { "," } "}"
   EXPR_LIST = { EXPR { "," EXPR } { "," } }
   */
-  const [, peak] = next(t);
-
-  if (peak.kind === "let") {
-    [t] = expectNext(t, "let");
-    let name;
-    [t, name] = expectNext<TokenIdent>(t, "identifier");
-
-    let type = undefined;
-    let colon;
-    [t, colon] = eat(t, ":");
-    if (colon) {
-      [t, type] = parseType(t);
-    }
-
-    [t] = expectNext(t, "=");
-    let rhs;
-    [t, rhs] = parseExpr(t);
-    [t] = expectNext(t, "in");
-    let after;
-    [t, after] = parseExpr(t);
-
-    return [
-      t,
-      { kind: "let", name: name.ident, type, rhs, after, span: name.span },
-    ];
-  }
-
-  if (peak.kind === "if") {
-    [t] = expectNext(t, "if");
-    let cond;
-    [t, cond] = parseExpr(t);
-    [t] = expectNext(t, "then");
-    let then;
-    [t, then] = parseExpr(t);
-
-    let elseTok;
-    [t, elseTok] = eat(t, "else");
-    let elsePart = undefined;
-    if (elseTok) {
-      [t, elsePart] = parseExpr(t);
-    }
-
-    return [t, { kind: "if", cond, then, else: elsePart, span: peak.span }];
-  }
-
   return parseExprComparison(t);
 }
 
@@ -206,15 +169,15 @@ function mkParserExprBinary(
     let lhs;
     [t, lhs] = lower(t);
 
-    const [, peak] = next(t);
-    if (kinds.includes(peak.kind)) {
+    const [, peek] = next(t);
+    if (kinds.includes(peek.kind)) {
       [t] = next(t);
       let rhs;
       [t, rhs] = parser(t);
-      const span = peak.span;
+      const span = spanMerge(lhs.span, rhs.span);
       return [
         t,
-        { kind: "binary", binaryKind: peak.kind as BinaryKind, lhs, rhs, span },
+        { kind: "binary", binaryKind: peek.kind as BinaryKind, lhs, rhs, span },
       ];
     }
 
@@ -318,8 +281,6 @@ function parseExprAtom(startT: Token[]): [Token[], Expr] {
   }
 
   if (tok.kind === "identifier") {
-    console.log(t);
-
     if (maybeNextT(t)[1]?.kind === "{") {
       let fields;
       [t, fields] = parseStructInit(t);
@@ -344,6 +305,52 @@ function parseExprAtom(startT: Token[]): [Token[], Expr] {
     ];
   }
 
+  if (tok.kind === "let") {
+    let name;
+    [t, name] = expectNext<TokenIdent>(t, "identifier");
+
+    let type = undefined;
+    let colon;
+    [t, colon] = eat(t, ":");
+    if (colon) {
+      [t, type] = parseType(t);
+    }
+
+    [t] = expectNext(t, "=");
+    let rhs;
+    [t, rhs] = parseExpr(t);
+
+    const nameIdent: Identifier = { name: name.ident, span: name.span };
+
+    return [
+      t,
+      {
+        kind: "let",
+        name: nameIdent,
+        type,
+        rhs,
+        span: name.span,
+      },
+    ];
+  }
+
+  if (tok.kind === "if") {
+    let cond;
+    [t, cond] = parseExpr(t);
+    [t] = expectNext(t, "then");
+    let then;
+    [t, then] = parseExpr(t);
+
+    let elseTok;
+    [t, elseTok] = eat(t, "else");
+    let elsePart = undefined;
+    if (elseTok) {
+      [t, elsePart] = parseExpr(t);
+    }
+
+    return [t, { kind: "if", cond, then, else: elsePart, span: tok.span }];
+  }
+
   // Parse nothing at all.
   return [startT, { kind: "empty", span }];
 }
@@ -496,3 +503,30 @@ function maybeNextT(t: Token[]): [Token[], Token | undefined] {
 function unexpectedToken(token: Token): never {
   throw new CompilerError("unexpected token", token.span);
 }
+
+function validateAst(ast: Ast) {
+  const validator: Folder = {
+    ...DEFAULT_FOLDER,
+    expr(value: Expr): Expr {
+      if (value.kind === "block") {
+        value.exprs.forEach((expr) => {
+          if (expr.kind === "let") {
+            this.expr(expr.rhs);
+            if (expr.type) {
+              this.type(expr.type);
+            }
+          } else {
+            this.expr(expr);
+          }
+        });
+        return value;
+      } else if (value.kind === "let") {
+        throw new CompilerError("let is only allowed in blocks", value.span);
+      } else {
+        return superFoldExpr(value, this);
+      }
+    },
+  };
+
+  foldAst(ast, validator);
+}
diff --git a/src/printer.ts b/src/printer.ts
index d801d0b..90c6ebd 100644
--- a/src/printer.ts
+++ b/src/printer.ts
@@ -53,10 +53,10 @@ function printExpr(expr: Expr, indent: number): string {
     case "let": {
       const type = expr.type ? `: ${printType(expr.type)}` : "";
 
-      return `let ${expr.name}${type} = ${printExpr(
+      return `let ${expr.name.name}${type} = ${printExpr(
         expr.rhs,
         indent + 1
-      )} in${linebreak(indent)}${printExpr(expr.after, indent)}`;
+      )}`;
     }
     case "block": {
       const exprs = expr.exprs.map((expr) => printExpr(expr, indent + 1));
diff --git a/src/resolve.ts b/src/resolve.ts
index d01b53a..a5b4423 100644
--- a/src/resolve.ts
+++ b/src/resolve.ts
@@ -3,8 +3,10 @@ import {
   BUILTINS,
   BuiltinName,
   DEFAULT_FOLDER,
+  Expr,
   Folder,
   Identifier,
+  LocalInfo,
   Resolution,
   foldAst,
   superFoldExpr,
@@ -68,6 +70,8 @@ export function resolve(ast: Ast): Ast {
     throw new CompilerError(`cannot find ${ident.name}`, ident.span);
   };
 
+  const blockLocals: LocalInfo[][] = [];
+
   const resolver: Folder = {
     ...DEFAULT_FOLDER,
     item(item) {
@@ -82,7 +86,7 @@ export function resolve(ast: Ast): Ast {
             item.node.returnType && this.type(item.node.returnType);
 
           item.node.params.forEach(({ name }) => scopes.push(name));
-          const body = superFoldExpr(item.node.body, this);
+          const body = this.expr(item.node.body);
           const revParams = item.node.params.slice();
           revParams.reverse();
           revParams.forEach(({ name }) => popScope(name));
@@ -104,24 +108,39 @@ export function resolve(ast: Ast): Ast {
       return superFoldItem(item, this);
     },
     expr(expr) {
-      if (expr.kind === "let") {
-        const rhs = this.expr(expr.rhs);
-        const type = expr.type && this.type(expr.type);
-        scopes.push(expr.name);
-        const after = this.expr(expr.after);
-        popScope(expr.name);
+      if (expr.kind === "block") {
+        const prevScopeLength = scopes.length;
+        blockLocals.push([]);
+
+        const exprs = expr.exprs.map<Expr>((inner) => this.expr(inner));
+
+        scopes.length = prevScopeLength;
+        const locals = blockLocals.pop();
 
         return {
-          kind: "let",
-          name: expr.name,
-          rhs,
-          after,
-          type,
+          kind: "block",
+          exprs,
+          locals,
           span: expr.span,
         };
-      }
+      } else if (expr.kind === "let") {
+        let rhs = this.expr(expr.rhs);
+        let type = expr.type && this.type(expr.type);
 
-      return superFoldExpr(expr, this);
+        scopes.push(expr.name.name);
+        const local = { name: expr.name.name, span: expr.name.span };
+        blockLocals[blockLocals.length - 1].push(local);
+
+        return {
+          ...expr,
+          name: expr.name,
+          local,
+          type,
+          rhs,
+        };
+      } else {
+        return superFoldExpr(expr, this);
+      }
     },
     ident(ident) {
       const res = resolveIdent(ident);
diff --git a/src/typeck.ts b/src/typeck.ts
index 26e1cbc..8dcdb91 100644
--- a/src/typeck.ts
+++ b/src/typeck.ts
@@ -425,9 +425,11 @@ export function checkBody(
           const rhs = this.expr(expr.rhs);
           infcx.assign(bindingTy, rhs.ty!, expr.span);
 
+          // AST validation ensures that lets can only be in blocks, where
+          // the types will be popped.
           localTys.push(bindingTy);
-          const after = this.expr(expr.after);
-          localTys.pop();
+
+          expr.local!.ty = bindingTy;
 
           const type: Type | undefined = loweredBindingTy && {
             ...expr.type!,
@@ -439,20 +441,23 @@ export function checkBody(
             name: expr.name,
             type,
             rhs,
-            after,
-            ty: after.ty!,
+            ty: TY_UNIT,
             span: expr.span,
           };
         }
         case "block": {
+          const prevLocalTysLen = localTys.length;
+
           const exprs = expr.exprs.map((expr) => this.expr(expr));
+
           const ty = exprs.length > 0 ? exprs[exprs.length - 1].ty! : TY_UNIT;
 
+          localTys.length = prevLocalTysLen;
+
           return {
-            kind: "block",
+            ...expr,
             exprs,
             ty,
-            span: expr.span,
           };
         }
         case "literal": {
@@ -592,13 +597,25 @@ export function checkBody(
 
   infcx.assign(fnTy.returnTy, checked.ty!, body.span);
 
+  const resolveTy = (ty: Ty, span: Span) => {
+    const resTy = infcx.resolveIfPossible(ty);
+    if (!resTy) {
+      throw new CompilerError("cannot infer type", span);
+    }
+    return resTy;
+  };
+
   const resolver: Folder = {
     ...DEFAULT_FOLDER,
     expr(expr) {
-      const ty = infcx.resolveIfPossible(expr.ty!);
-      if (!ty) {
-        throw new CompilerError("cannot infer type", expr.span);
+      const ty = resolveTy(expr.ty!, expr.span);
+
+      if (expr.kind === "block") {
+        expr.locals!.forEach((local) => {
+          local.ty = resolveTy(local.ty!, local.span);
+        });
       }
+
       return { ...expr, ty };
     },
   };