diff --git a/compiler/ast/ast.ts b/compiler/ast/ast.ts
index 2a16763..4fe94be 100644
--- a/compiler/ast/ast.ts
+++ b/compiler/ast/ast.ts
@@ -5,22 +5,149 @@ export type File = {
 };
 
 export type Stmt = {
-    id: number;
     kind: StmtKind;
     span: Span;
 };
 
 export type StmtKind =
     | { tag: "error" }
-    | { tag: "mod_block" } & ModBlockStmt
-    | { tag: "mod_file" } & ModFileStmt;
+    | { tag: "item" } & ItemStmt
+    | { tag: "let" } & LetStmt
+    | { tag: "return" } & ReturnStmt
+    | { tag: "break" } & BreakStmt
+    | { tag: "assign" } & AssignStmt
+    | { tag: "expr" } & ExprStmt;
 
-export type ModBlockStmt = {
-    ident: string;
+export type ItemStmt = { item: Item };
+
+export type LetStmt = {
+    subject: Pat;
+    expr?: Expr;
+};
+
+export type ReturnStmt = { expr?: Expr };
+export type BreakStmt = { expr?: Expr };
+
+export type AssignStmt = {
+    assignType: AssignType;
+    subject: Expr;
+    value: Expr;
+};
+
+export type AssignType = "=" | "+=" | "-=";
+
+export type ExprStmt = { expr: Expr };
+
+export type Item = {
+    kind: ItemKind;
+    span: Span;
+    ident: Ident;
+    pub: boolean;
+};
+
+export type ItemKind =
+    | { tag: "error" }
+    | { tag: "mod_block" } & ModBlockItem
+    | { tag: "mod_file" } & ModFileItem
+    | { tag: "enum" } & EnumItem
+    | { tag: "struct" } & StructItem
+    | { tag: "fn" } & FnItem
+    | { tag: "use" } & UseItem
+    | { tag: "static" } & StaticItem
+    | { tag: "type_alias" } & TypeAliasItem;
+
+export type ModBlockItem = {
+    ident: Ident;
     stmts: Stmt[];
 };
 
-export type ModFileStmt = {
-    ident: string;
+export type ModFileItem = {
+    ident: Ident;
     filePath: string;
 };
+
+export type EnumItem = { variants: Variant[] };
+export type StructItem = { data: VariantData };
+export type FnItem = { _: 0 };
+export type UseItem = { _: 0 };
+export type StaticItem = { _: 0 };
+export type TypeAliasItem = { _: 0 };
+
+export type Variant = {
+    ident: Ident;
+    data: VariantData;
+    pub: boolean;
+    span: Span;
+};
+
+export type VariantData = {
+    kind: VariantDataKind;
+    span: Span;
+};
+
+export type VariantDataKind =
+    | { tag: "error" }
+    | { tag: "unit" }
+    | { tag: "tuple" } & TupleVariantData
+    | { tag: "struct" } & StructVariantData;
+
+export type TupleVariantData = { elems: VariantData[] };
+export type StructVariantData = { fields: FieldDef[] };
+
+export type FieldDef = {
+    ident: Ident;
+    ty: Ty;
+    pub: boolean;
+    span: Span;
+};
+
+export type Expr = {
+    kind: ExprKind;
+    span: Span;
+};
+
+export type ExprKind =
+    | { tag: "error" }
+    | { tag: "ident" } & Ident;
+
+export type Pat = {
+    kind: PatKind;
+    span: Span;
+};
+
+export type PatKind =
+    | { tag: "error" }
+    | { tag: "bind" } & BindPat;
+
+export type BindPat = {
+    ident: Ident;
+    mut: boolean;
+};
+
+export type Ty = {
+    kind: TyKind;
+    span: Span;
+};
+
+export type TyKind =
+    | { tag: "error" }
+    | { tag: "ident" } & Ident
+    | { tag: "ref" } & RefTy
+    | { tag: "ptr" } & PtrTy
+    | { tag: "slice" } & SliceTy
+    | { tag: "array" } & ArrayTy;
+
+export type RefTy = { ty: Ty; mut: boolean };
+export type PtrTy = { ty: Ty; mut: boolean };
+export type SliceTy = { ty: Ty };
+export type ArrayTy = { ty: Ty; length: Expr };
+export type TupleTy = { elems: Ty[] };
+export type StructTy = { fields: FieldDef[] };
+
+export type AnonFieldDef = {
+    ident: Ident;
+    ty: Ty;
+    span: Span;
+};
+
+export type Ident = { text: string; span: Span };
diff --git a/compiler/ast/visitor.ts b/compiler/ast/visitor.ts
index 7c4ed88..17b9bd0 100644
--- a/compiler/ast/visitor.ts
+++ b/compiler/ast/visitor.ts
@@ -1,5 +1,32 @@
 import { exhausted } from "../util.ts";
-import { File, ModBlockStmt, ModFileStmt, Stmt } from "./ast.ts";
+import {
+    ArrayTy,
+    AssignStmt,
+    BindPat,
+    BreakStmt,
+    EnumItem,
+    Expr,
+    ExprStmt,
+    File,
+    FnItem,
+    Ident,
+    Item,
+    ItemStmt,
+    LetStmt,
+    ModBlockItem,
+    ModFileItem,
+    Pat,
+    PtrTy,
+    RefTy,
+    ReturnStmt,
+    SliceTy,
+    StaticItem,
+    Stmt,
+    StructItem,
+    Ty,
+    TypeAliasItem,
+    UseItem,
+} from "./ast.ts";
 
 export type VisitRes = "stop" | void;
 
@@ -12,8 +39,36 @@ export interface Visitor<
     visitFile?(file: File, ...p: P): R;
     visitStmt?(stmt: Stmt, ...p: P): R;
     visitErrorStmt?(stmt: Stmt, ...p: P): R;
-    visitModBlockStmt?(stmt: Stmt, kind: ModBlockStmt, ...p: P): R;
-    visitModFileStmt?(stmt: Stmt, kind: ModFileStmt, ...p: P): R;
+    visitItemStmt?(stmt: Stmt, kind: ItemStmt, ...p: P): R;
+    visitLetStmt?(stmt: Stmt, kind: LetStmt, ...p: P): R;
+    visitReturnStmt?(stmt: Stmt, kind: ReturnStmt, ...p: P): R;
+    visitBreakStmt?(stmt: Stmt, kind: BreakStmt, ...p: P): R;
+    visitAssignStmt?(stmt: Stmt, kind: AssignStmt, ...p: P): R;
+    visitExprStmt?(stmt: Stmt, kind: ExprStmt, ...p: P): R;
+    visitItem?(item: Item, ...p: P): R;
+    visitErrorItem?(item: Item, ...p: P): R;
+    visitModBlockItem?(item: Item, kind: ModBlockItem, ...p: P): R;
+    visitModFileItem?(item: Item, kind: ModFileItem, ...p: P): R;
+    visitEnumItem?(item: Item, kind: EnumItem, ...p: P): R;
+    visitStructItem?(item: Item, kind: StructItem, ...p: P): R;
+    visitFnItem?(item: Item, kind: FnItem, ...p: P): R;
+    visitUseItem?(item: Item, kind: UseItem, ...p: P): R;
+    visitStaticItem?(item: Item, kind: StaticItem, ...p: P): R;
+    visitTypeAliasItem?(item: Item, kind: TypeAliasItem, ...p: P): R;
+    visitExpr?(expr: Expr, ...p: P): R;
+    visitErrorExpr?(expr: Expr, ...p: P): R;
+    visitIdentExpr?(expr: Expr, kind: Ident, ...p: P): R;
+    visitPat?(pat: Pat, ...p: P): R;
+    visitErrorPat?(pat: Pat, ...p: P): R;
+    visitBindPat?(pat: Pat, kind: BindPat, ...p: P): R;
+    visitTy?(ty: Ty, ...p: P): R;
+    visitErrorTy?(ty: Ty, ...p: P): R;
+    visitIdentTy?(ty: Ty, kind: Ident, ...p: P): R;
+    visitRefTy?(ty: Ty, kind: RefTy, ...p: P): R;
+    visitPtrTy?(ty: Ty, kind: PtrTy, ...p: P): R;
+    visitSliceTy?(ty: Ty, kind: SliceTy, ...p: P): R;
+    visitArrayTy?(ty: Ty, kind: ArrayTy, ...p: P): R;
+    visitIdent?(ident: Ident, ...p: P): R;
 }
 
 export function visitFile<
@@ -46,17 +101,136 @@ export function visitStmt<
     stmt: Stmt,
     ...p: P
 ) {
-    switch (stmt.kind.tag) {
+    const kind = stmt.kind;
+    switch (kind.tag) {
         case "error":
             if (v.visitErrorStmt?.(stmt, ...p) === "stop") return;
             return;
-        case "mod_block":
-            if (v.visitModBlockStmt?.(stmt, stmt.kind, ...p) === "stop") return;
-            visitStmts(v, stmt.kind.stmts, ...p);
+        case "item":
+            if (v.visitItemStmt?.(stmt, kind, ...p) === "stop") return;
             return;
-        case "mod_file":
-            if (v.visitModFileStmt?.(stmt, stmt.kind, ...p) === "stop") return;
+        case "let":
+            if (v.visitLetStmt?.(stmt, kind, ...p) === "stop") return;
+            return;
+        case "return":
+            if (v.visitReturnStmt?.(stmt, kind, ...p) === "stop") return;
+            return;
+        case "break":
+            if (v.visitBreakStmt?.(stmt, kind, ...p) === "stop") return;
+            return;
+        case "assign":
+            if (v.visitAssignStmt?.(stmt, kind, ...p) === "stop") return;
+            return;
+        case "expr":
+            if (v.visitExprStmt?.(stmt, kind, ...p) === "stop") return;
             return;
     }
-    exhausted(stmt.kind);
+    exhausted(kind);
+}
+
+export function visitItem<
+    P extends PM = [],
+>(
+    v: Visitor<P>,
+    item: Item,
+    ...p: P
+) {
+    const kind = item.kind;
+    switch (kind.tag) {
+        case "error":
+            if (v.visitErrorItem?.(item, ...p) === "stop") return;
+            return;
+        case "mod_block":
+            if (v.visitModBlockItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "mod_file":
+            if (v.visitModFileItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "enum":
+            if (v.visitEnumItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "struct":
+            if (v.visitStructItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "fn":
+            if (v.visitFnItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "use":
+            if (v.visitUseItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "static":
+            if (v.visitStaticItem?.(item, kind, ...p) === "stop") return;
+            return;
+        case "type_alias":
+            if (v.visitTypeAliasItem?.(item, kind, ...p) === "stop") return;
+            return;
+    }
+    exhausted(kind);
+}
+
+export function visitExpr<
+    P extends PM = [],
+>(
+    v: Visitor<P>,
+    expr: Expr,
+    ...p: P
+) {
+    const kind = expr.kind;
+    switch (kind.tag) {
+        case "error":
+            if (v.visitErrorExpr?.(expr, ...p) === "stop") return;
+            return;
+        case "ident":
+            if (v.visitIdentExpr?.(expr, kind, ...p) === "stop") return;
+            return;
+    }
+    exhausted(kind);
+}
+
+export function visitPat<
+    P extends PM = [],
+>(
+    v: Visitor<P>,
+    pat: Pat,
+    ...p: P
+) {
+    const kind = pat.kind;
+    switch (kind.tag) {
+        case "error":
+            if (v.visitErrorPat?.(pat, ...p) === "stop") return;
+            return;
+        case "bind":
+            if (v.visitBindPat?.(pat, kind, ...p) === "stop") return;
+            return;
+    }
+    exhausted(kind);
+}
+
+export function visitTy<
+    P extends PM = [],
+>(
+    v: Visitor<P>,
+    ty: Ty,
+    ...p: P
+) {
+    const kind = ty.kind;
+    switch (kind.tag) {
+        case "error":
+            if (v.visitErrorTy?.(ty, ...p) === "stop") return;
+            return;
+        case "ident":
+            if (v.visitIdentTy?.(ty, kind, ...p) === "stop") return;
+            return;
+    }
+    exhausted(kind);
+}
+
+export function visitIdent<
+    P extends PM = [],
+>(
+    v: Visitor<P>,
+    ident: Ident,
+    ...p: P
+) {
+    v.visitIdent?.(ident, ...p);
 }
diff --git a/compiler/main.ts b/compiler/main.ts
index 5dcf461..6cbe952 100644
--- a/compiler/main.ts
+++ b/compiler/main.ts
@@ -15,20 +15,25 @@ export interface PackEmitter {
 }
 
 export class PackCompiler {
+    private ctx = new Ctx();
+
     public constructor(
         private entryFilePath: string,
         private emitter: PackEmitter,
     ) {}
 
     public compile() {
+        FileTreeAstCollector
+            .fromEntryFile(this.ctx, this.entryFilePath)
+            .collect();
     }
 }
 
 type _P = { file: File };
-export class FileTreeCollector implements ast.Visitor<[_P]> {
+export class FileTreeAstCollector implements ast.Visitor<[_P]> {
     private subFilePromise = Promise.resolve();
 
-    public constructor(
+    private constructor(
         private ctx: Ctx,
         private superFile: File | undefined,
         private ident: string,
@@ -36,6 +41,19 @@ export class FileTreeCollector implements ast.Visitor<[_P]> {
         private relPath: string,
     ) {}
 
+    public static fromEntryFile(
+        ctx: Ctx,
+        entryFilePath: string,
+    ): FileTreeAstCollector {
+        return new FileTreeAstCollector(
+            ctx,
+            undefined,
+            "root",
+            entryFilePath,
+            entryFilePath,
+        );
+    }
+
     public async collect(): Promise<void> {
         const text = await Deno.readTextFile(this.absPath);
         const file = this.ctx.addFile(
@@ -51,12 +69,12 @@ export class FileTreeCollector implements ast.Visitor<[_P]> {
         await this.subFilePromise;
     }
 
-    visitModFileStmt(
-        stmt: ast.Stmt,
-        kind: ast.ModFileStmt,
+    visitModFileItem(
+        item: ast.Item,
+        kind: ast.ModFileItem,
         { file }: _P,
     ): ast.VisitRes {
-        const { ident, filePath: relPath } = kind;
+        const { ident: { text: ident }, filePath: relPath } = kind;
         const absPath = path.join(path.dirname(this.absPath), relPath);
         this.subFilePromise = this.subFilePromise
             .then(() => {
@@ -65,10 +83,11 @@ export class FileTreeCollector implements ast.Visitor<[_P]> {
                         severity: "fatal",
                         msg: `module '${ident}' already declared`,
                         file,
-                        span: stmt.span,
+                        span: item.span,
                     });
+                    Deno.exit(1);
                 }
-                return new FileTreeCollector(
+                return new FileTreeAstCollector(
                     this.ctx,
                     file,
                     ident,