diff --git a/example.lang4 b/example.lang4
index a656dd0..7e469d1 100644
--- a/example.lang4
+++ b/example.lang4
@@ -4,8 +4,13 @@ fn main() -> int {
     
     let ch = 'c';
     let s = "hello\ world";
+    
+    inner();
+
+    fn inner() {
+        print_int(v);
+    }
 
-    print_int(v);
     print_str(v);
 }
 
diff --git a/src/ast.ts b/src/ast.ts
index 79e5ac6..80e3d33 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -173,6 +173,10 @@ export class Ty {
 
 export type TyKind =
     | { tag: "error" }
+    | { tag: "int" }
+    | { tag: "bool" }
+    | { tag: "char" }
+    | { tag: "str" }
     | { tag: "ident"; ident: string };
 
 export const VisitorBreak = Symbol();
diff --git a/src/main.ts b/src/main.ts
index 3c4e299..5084c0a 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -10,11 +10,22 @@ async function main() {
 
     const parser = new Parser(toks);
     const file = parser.parseFile();
+    if (parser.errorOccured) {
+        console.error("parsing failed");
+        Deno.exit(1);
+    }
 
     // console.log(yaml.stringify({ file }, { skipInvalid: true, indent: 2 }));
     // console.log(JSON.stringify({ file }, null, 2));
 
-    file.visit(new Resolver());
+    const resolver = new Resolver();
+    const syms = resolver.resolveFile(file);
+    if (resolver.errorOccured) {
+        console.error("resolving failed");
+        Deno.exit(1);
+    }
+
+    console.log(syms);
 
     // console.log(cx);
 }
diff --git a/src/parse.ts b/src/parse.ts
index 3a125e2..c058406 100644
--- a/src/parse.ts
+++ b/src/parse.ts
@@ -190,7 +190,15 @@ export class Parser {
 
     parseTy(): Ty {
         const line = this.line();
-        if (this.eat("ident")) {
+        if (this.eat("int")) {
+            return t.ty(line, "int", {});
+        } else if (this.eat("bool")) {
+            return t.ty(line, "bool", {});
+        } else if (this.eat("char")) {
+            return t.ty(line, "char", {});
+        } else if (this.eat("str")) {
+            return t.ty(line, "str", {});
+        } else if (this.eat("ident")) {
             const ident = this.eaten!.value!;
             return t.ty(line, "ident", { ident });
         } else {
@@ -242,7 +250,9 @@ export class Parser {
         return this.i >= this.toks.length;
     }
 
+    public errorOccured = false;
     private error(line: number, message: string) {
+        this.errorOccured = true;
         console.error(
             `%cerror%c: ${message}\n %c--> line ${line}%c`,
             "font-weight: bold; color: red",
diff --git a/src/resolve.ts b/src/resolve.ts
index 621858c..a6d8345 100644
--- a/src/resolve.ts
+++ b/src/resolve.ts
@@ -1,9 +1,56 @@
-import { Pat, Stmt, Visitor, VisitorBreak } from "./ast.ts";
+import {
+    Block,
+    Expr,
+    File,
+    Pat,
+    Stmt,
+    Ty,
+    Visitor,
+    VisitorBreak,
+} from "./ast.ts";
+
+class Res {
+    constructor(
+        private kind: ResKind,
+    ) {}
+
+    is(tag: ResKind["tag"]): boolean {
+        return this.kind.tag === tag;
+    }
+}
+
+type ResKind =
+    | { tag: "unresolved" }
+    | { tag: "fn"; def: Def }
+    | { tag: "local"; def: Def };
 
 export class Def {
     constructor(
-        kind: DefKind,
+        private kind: DefKind,
     ) {}
+
+    resolve(): Res {
+        const k = this.kind;
+        switch (k.tag) {
+            case "fn":
+                return new Res({ tag: "fn", def: this });
+            case "param":
+            case "let":
+                return new Res({ tag: "local", def: this });
+        }
+    }
+
+    line(): number {
+        const k = this.kind;
+        switch (k.tag) {
+            case "fn":
+                return k.stmt.line;
+            case "param":
+                return k.pat.line;
+            case "let":
+                return k.pat.line;
+        }
+    }
 }
 
 export type DefKind =
@@ -11,6 +58,10 @@ export type DefKind =
     | { tag: "param"; stmt: Stmt; pat: Pat }
     | { tag: "let"; stmt: Stmt; pat: Pat };
 
+type DefineResult =
+    | { ok: true }
+    | { ok: false; error: "redefinition"; originalDef: Def };
+
 export class Rib {
     private syms = new Map<string, Def>();
 
@@ -18,64 +69,231 @@ export class Rib {
         private kind: RibKind,
     ) {}
 
-    define(ident: string, def: Def) {
+    define(ident: string, def: Def): DefineResult {
+        if (this.syms.has(ident)) {
+            return {
+                ok: false,
+                error: "redefinition",
+                originalDef: this.syms.get(ident)!,
+            };
+        }
         this.syms.set(ident, def);
+        return { ok: true };
+    }
+
+    resolve(ident: string): Res {
+        const k = this.kind;
+        const sym = this.syms.get(ident);
+        if (!sym) {
+            if (k.tag === "root") {
+                return new Res({ tag: "unresolved" });
+            }
+            return k.parent.resolve(ident);
+        }
+        const res = sym.resolve();
+        if (k.tag === "fn" && res.is("local")) {
+            return new Res({ tag: "unresolved" });
+        }
+        return res;
     }
 }
 
 export type RibKind =
     | { tag: "root" }
     | { tag: "fn"; parent: Rib }
+    | { tag: "param"; parent: Rib }
     | { tag: "block"; parent: Rib }
     | { tag: "let"; parent: Rib };
 
+export class Syms {
+    constructor(
+        private astNodeDefs: Map<number, Res>,
+    ) {}
+
+    exprRes(expr: Expr): Res {
+        const res = this.astNodeDefs.get(expr.id);
+        if (!res) throw new Error();
+        return res;
+    }
+
+    patRes(pat: Pat): Res {
+        const res = this.astNodeDefs.get(pat.id);
+        if (!res) throw new Error();
+        return res;
+    }
+
+    tyRes(ty: Ty): Res {
+        const res = this.astNodeDefs.get(ty.id);
+        if (!res) throw new Error();
+        return res;
+    }
+}
+
 export class Resolver implements Visitor {
     private rib = new Rib({ tag: "root" });
-    private ribStateStack: Rib[] = [];
+    private scopeStack: Rib[] = [];
+    private astNodeDefs = new Map<number, Res>();
 
-    pushRib<Tag extends RibKind["tag"]>(
-        tag: Tag,
-        kind: Omit<RibKind & { tag: Tag }, "tag" | "parent">,
-    ) {
-        this.rib = new Rib({ tag, parent: this.rib, ...kind } as RibKind);
-    }
+    resolveFile(file: File): Syms {
+        file.visit({
+            visitStmt: (stmt): void | VisitorBreak => {
+                const k = stmt.kind;
+                if (k.tag === "fn") {
+                    this.tryDefine(
+                        stmt.line,
+                        k.ident,
+                        new Def({ tag: "fn", stmt }),
+                    );
+                }
+                return VisitorBreak;
+            },
+        });
 
-    saveRibState() {
-        this.ribStateStack.push(this.rib);
-    }
-
-    restoreRibState() {
-        this.rib = this.ribStateStack.pop()!;
-    }
-
-    define(ident: string, def: Def) {
-        this.rib.define(ident, def);
+        file.visit(this);
+        return new Syms(this.astNodeDefs);
     }
 
     visitStmt(stmt: Stmt): void | VisitorBreak {
         const k = stmt.kind;
         if (k.tag === "fn") {
-            this.define(k.ident, new Def({ tag: "fn", stmt }));
-            this.saveRibState();
+            this.saveScope();
             this.pushRib("fn", {});
-            k.params.forEach((param) => param.visit(this));
+
+            k.body.visit({
+                visitStmt: (stmt): void | VisitorBreak => {
+                    const k = stmt.kind;
+                    if (k.tag === "fn") {
+                        this.tryDefine(
+                            stmt.line,
+                            k.ident,
+                            new Def({ tag: "fn", stmt }),
+                        );
+                    }
+                    return VisitorBreak;
+                },
+            });
+
+            this.pushRib("param", {});
+            for (const param of k.params) {
+                param.pat.visit({
+                    visitPat: (pat: Pat) => {
+                        const k = pat.kind;
+                        if (k.tag !== "ident") {
+                            return;
+                        }
+                        this.tryDefine(
+                            pat.line,
+                            k.ident,
+                            new Def({ tag: "param", stmt, pat }),
+                        );
+                    },
+                });
+            }
+
             k.retTy?.visit(this);
             k.body.visit(this);
-            this.restoreRibState();
+
+            this.restoreScope();
             return VisitorBreak;
         } else if (k.tag === "let") {
             this.pushRib("let", {});
             k.param.pat.visit({
                 visitPat: (pat: Pat) => {
                     const k = pat.kind;
-                    if (k.tag === "ident") {
-                        this.define(
-                            k.ident,
-                            new Def({ tag: "let", stmt, pat }),
-                        );
+                    if (k.tag !== "ident") {
+                        return;
                     }
+                    this.tryDefine(
+                        pat.line,
+                        k.ident,
+                        new Def({ tag: "let", stmt, pat }),
+                    );
                 },
             });
         }
     }
+
+    visitBlock(block: Block): void | VisitorBreak {
+        this.saveScope();
+        this.pushRib("block", {});
+        block.stmts.forEach((stmt) => stmt.visit(this));
+        block.expr?.visit(this);
+        this.restoreScope();
+        return VisitorBreak;
+    }
+
+    visitExpr(expr: Expr): void | VisitorBreak {
+        const k = expr.kind;
+        if (k.tag !== "ident") {
+            return;
+        }
+        const res = this.resolve(expr.line, k.ident);
+        this.astNodeDefs.set(expr.id, res);
+    }
+
+    visitTy(ty: Ty): void | VisitorBreak {
+        const k = ty.kind;
+        if (k.tag !== "ident") {
+            return;
+        }
+        const res = this.resolve(ty.line, k.ident);
+        this.astNodeDefs.set(ty.id, res);
+    }
+
+    private pushRib<Tag extends RibKind["tag"]>(
+        tag: Tag,
+        kind: Omit<RibKind & { tag: Tag }, "tag" | "parent">,
+    ) {
+        this.rib = new Rib({ tag, parent: this.rib, ...kind } as RibKind);
+    }
+
+    private saveScope() {
+        this.scopeStack.push(this.rib);
+    }
+
+    private restoreScope() {
+        this.rib = this.scopeStack.pop()!;
+    }
+
+    private tryDefine(line: number, ident: string, def: Def) {
+        const result = this.define(ident, def);
+        if (!result.ok) {
+            this.error(line, `redefinition of '${ident}'`);
+            this.info(result.originalDef.line(), `'${ident}' defined here`);
+        }
+    }
+
+    private define(ident: string, def: Def): DefineResult {
+        return this.rib.define(ident, def);
+    }
+
+    private resolve(line: number, ident: string): Res {
+        const res = this.rib.resolve(ident);
+        if (res.is("unresolved")) {
+            this.error(line, `unresolved ident '${ident}'`);
+        }
+        return res;
+    }
+
+    public errorOccured = false;
+    private error(line: number, message: string) {
+        this.errorOccured = true;
+        console.error(
+            `%cerror%c: ${message}\n %c--> line ${line}%c`,
+            "font-weight: bold; color: red",
+            "font-weight: bold; color: while",
+            "color: cyan",
+            "",
+        );
+    }
+
+    private info(line: number, message: string) {
+        console.error(
+            `%cinfo%c: ${message}\n %c--> line ${line}%c`,
+            "font-weight: bold; color: blue",
+            "font-weight: bold; color: while",
+            "color: cyan",
+            "",
+        );
+    }
 }
diff --git a/src/tok.ts b/src/tok.ts
index 3baeccf..5d83357 100644
--- a/src/tok.ts
+++ b/src/tok.ts
@@ -5,10 +5,14 @@ export type Tok = {
 };
 
 const keywords = new Set([
-    "fn",
-    "let",
     "true",
     "false",
+    "bool",
+    "int",
+    "char",
+    "str",
+    "fn",
+    "let",
 ]);
 
 type OpTree = Map<string, OpTree | null>;