diff --git a/slige/compiler/main.ts b/slige/compiler/main.ts
index 765a2de..fcb1cae 100644
--- a/slige/compiler/main.ts
+++ b/slige/compiler/main.ts
@@ -1,10 +1,10 @@
 import * as path from "jsr:@std/path";
 import { Parser } from "./parse/parser.ts";
-import * as ast from "./ast/mod.ts";
+import * as ast from "@slige/ast";
 import { Ctx, File } from "@slige/common";
 import { Resolver } from "./resolve/resolver.ts";
 import { Checker } from "./check/checker.ts";
-import { AstLowerer } from "./middle/ast_lower.ts";
+import { ast_lower, mir_lower } from "@slige/middle";
 import { HirStringifyer } from "@slige/stringify";
 
 async function main() {
@@ -53,7 +53,7 @@ export class PackCompiler {
             console.error("error(s) occurred.");
             Deno.exit(1);
         }
-        const astLowerer = new AstLowerer(
+        const astLowerer = new ast_lower.AstLowerer(
             this.ctx,
             resols,
             checker,
@@ -65,6 +65,16 @@ export class PackCompiler {
             Deno.exit(1);
         }
         console.log("=== MIR ===\n" + astLowerer.mirString());
+        if (this.ctx.errorOccured()) {
+            console.error("error(s) occurred. stopping...");
+            Deno.exit(1);
+        }
+        const mirLowerer = new mir_lower.MirLowerer(
+            this.ctx,
+            astLowerer.toArray(),
+        );
+        mirLowerer.lower();
+        console.log("=== LIR ===\n" + mirLowerer.lirString());
     }
 
     public enableDebug() {
diff --git a/slige/compiler/middle/ast_lower.ts b/slige/compiler/middle/ast_lower.ts
index a540f07..d69efbe 100644
--- a/slige/compiler/middle/ast_lower.ts
+++ b/slige/compiler/middle/ast_lower.ts
@@ -35,6 +35,10 @@ export class AstLowerer implements ast.Visitor {
             .toArray()
             .join("\n");
     }
+
+    public toArray(): Fn[] {
+        return this.fns.values().toArray();
+    }
 }
 
 export class FnLowerer {
diff --git a/slige/compiler/middle/lir.ts b/slige/compiler/middle/lir.ts
new file mode 100644
index 0000000..4e1e5f3
--- /dev/null
+++ b/slige/compiler/middle/lir.ts
@@ -0,0 +1,62 @@
+import { IdBase, IdMap } from "@slige/common";
+import * as mir from "./mir.ts";
+import { BlockId } from "./mir.ts";
+
+export type Fn = {
+    mirFn: mir.Fn;
+    blocks: IdMap<BlockId, Block>;
+    locals: IdMap<LocalId, Local>;
+};
+
+export type LocalId = IdBase & { readonly _: unique symbol };
+
+export type Local = {
+    id: LocalId;
+    base: mir.LocalId;
+    version: number;
+};
+
+export type Block = {
+    id: mir.BlockId;
+    stmts: Stmt[];
+    ter: Ter;
+};
+
+export type Stmt = {
+    kind: StmtKind;
+};
+
+export type StmtKind =
+    | { tag: "error" }
+    | { tag: "assign"; local: LocalId; rval: RVal };
+
+export type Ter = {
+    kind: TerKind;
+};
+
+export type TerKind =
+    | { tag: "error" }
+    | { tag: "goto"; target: BlockId }
+    | {
+        tag: "switch";
+        discr: RVal;
+        targets: SwitchTarget[];
+        otherwise: BlockId;
+    }
+    | { tag: "return" };
+
+export type SwitchTarget = {
+    value: number;
+    target: BlockId;
+};
+
+export type PhiSource = {
+    local: LocalId;
+    branch: BlockId;
+};
+
+export type RVal =
+    | { tag: "error" }
+    | { tag: "phi"; sources: PhiSource[] }
+    | { tag: "use"; local: LocalId }
+    | { tag: "const"; val: mir.Const };
diff --git a/slige/compiler/middle/mir.ts b/slige/compiler/middle/mir.ts
index ec5763e..4984eaf 100644
--- a/slige/compiler/middle/mir.ts
+++ b/slige/compiler/middle/mir.ts
@@ -35,13 +35,15 @@ export type Stmt = {
 
 export type StmtKind =
     | { tag: "error" }
-    | { tag: "assign"; place: Place; rval: RVal }
+    | { tag: "assign" } & AssignStmt
     | { tag: "fake_read"; place: Place }
     | { tag: "deinit"; place: Place }
     | { tag: "live"; local: LocalId }
     | { tag: "dead"; local: LocalId }
     | { tag: "mention"; place: Place };
 
+export type AssignStmt = { place: Place; rval: RVal };
+
 export type Ter = {
     kind: TerKind;
 };
diff --git a/slige/compiler/middle/mir_lower.ts b/slige/compiler/middle/mir_lower.ts
new file mode 100644
index 0000000..ed9d276
--- /dev/null
+++ b/slige/compiler/middle/mir_lower.ts
@@ -0,0 +1,259 @@
+import * as mir from "./mir.ts";
+import * as lir from "./lir.ts";
+import { Ctx, exhausted, IdMap, Ids, todo } from "@slige/common";
+import { BlockId } from "./mir.ts";
+import { LirFnStringifyer } from "@slige/stringify";
+
+export class MirLowerer {
+    private lirFns: lir.Fn[] = [];
+
+    public constructor(
+        private ctx: Ctx,
+        private mirFns: mir.Fn[],
+    ) {}
+
+    public lower() {
+        for (const fn of this.mirFns) {
+            this.lirFns.push(new FnLowerer(fn).lower());
+        }
+    }
+
+    public lirString(): string {
+        return this.lirFns
+            .values()
+            .map((fn) => new LirFnStringifyer(this.ctx).fn(fn))
+            .toArray()
+            .join("\n");
+    }
+}
+
+export class FnLowerer {
+    private localIds = new Ids<lir.LocalId>();
+    private locals = new IdMap<lir.LocalId, lir.Local>();
+
+    private localVersionCounter = new IdMap<mir.LocalId, number>();
+
+    private blocks = new IdMap<BlockId, lir.Block>();
+
+    private blockLocals = new IdMap<BlockId, IdMap<mir.LocalId, lir.Local>>();
+
+    private currentBlockId?: BlockId;
+
+    public constructor(
+        private fn: mir.Fn,
+    ) {}
+
+    public lower(): lir.Fn {
+        for (const mirBlock of this.fn.blocks.values()) {
+            const lirBlock = this.lowerBlock(mirBlock);
+            this.blocks.set(lirBlock.id, lirBlock);
+        }
+        return {
+            mirFn: this.fn,
+            blocks: this.blocks,
+            locals: this.locals,
+        };
+    }
+
+    private lowerBlock(block: mir.Block): lir.Block {
+        this.currentBlockId = block.id;
+        this.blockLocals.set(block.id, new IdMap());
+        const stmts: lir.Stmt[] = [];
+
+        const locals = new IdMap<mir.LocalId, lir.Local>();
+        for (const mirId of this.fn.locals.keys()) {
+            const lirId = this.localIds.nextThenStep();
+            this.localVersionCounter.set(mirId, 0);
+            const local: lir.Local = {
+                id: lirId,
+                base: mirId,
+                version: block.id.rawId,
+            };
+            locals.set(mirId, local);
+            this.locals.set(lirId, local);
+            this.blockLocals.get(block.id)!.set(mirId, local);
+        }
+
+        const superBlocks = this.fn.blocks
+            .values()
+            .filter((b) => blockHasTarget(b, block.id))
+            .toArray();
+
+        if (block.id.rawId !== 0) {
+            for (const mirId of locals.keys()) {
+                const sources: lir.PhiSource[] = [];
+                for (const superBlock of superBlocks) {
+                    const local = this.blockLocals.get(superBlock.id)!.get(
+                        mirId,
+                    )!;
+                    sources.push({ branch: superBlock.id, local: local.id });
+                }
+                stmts.push(
+                    this.stmt({
+                        tag: "assign",
+                        local: locals.get(mirId)!.id,
+                        rval: { tag: "phi", sources },
+                    }),
+                );
+            }
+        }
+
+        for (const stmt of block.stmts) {
+            stmts.push(...this.lowerStmt(stmt));
+        }
+        const [s1, ter] = this.lowerTer(block.terminator);
+        stmts.push(...s1);
+        return { id: block.id, stmts, ter };
+    }
+
+    private lowerStmt(stmt: mir.Stmt): lir.Stmt[] {
+        const k = stmt.kind;
+        switch (k.tag) {
+            case "error":
+                return [this.stmt({ tag: "error" })];
+            case "assign":
+                return this.lowerAssignStmt(stmt, k);
+            case "fake_read":
+                return [this.stmt({ tag: "error" })];
+            case "deinit":
+                return todo();
+            case "live":
+                return todo();
+            case "dead":
+                return todo();
+            case "mention":
+                return todo();
+        }
+        exhausted(k);
+    }
+
+    private lowerAssignStmt(stmt: mir.Stmt, kind: mir.AssignStmt): lir.Stmt[] {
+        if (kind.place.proj.length !== 0) {
+            return todo();
+        }
+        const [s1, rval] = this.lowerRVal(kind.rval);
+
+        const version = this.localVersionCounter.get(kind.place.local)!;
+        this.localVersionCounter.set(kind.place.local, version + 1);
+
+        const lirId = this.localIds.nextThenStep();
+        this.blockLocals
+            .get(this.currentBlockId!)!
+            .set(kind.place.local, {
+                id: lirId,
+                base: kind.place.local,
+                version,
+            });
+
+        return [...s1, this.stmt({ tag: "assign", local: lirId, rval })];
+    }
+
+    private lowerRVal(rval: mir.RVal): [lir.Stmt[], lir.RVal] {
+        switch (rval.tag) {
+            case "error":
+                return [[], { tag: "error" }];
+            case "use": {
+                switch (rval.operand.tag) {
+                    case "error":
+                        return [[], { tag: "error" }];
+                    case "copy":
+                    case "move":
+                        return [[], {
+                            tag: "use",
+                            local: this.blockLocals
+                                .get(this.currentBlockId!)!
+                                .get(rval.operand.place.local)!.id,
+                        }];
+                    case "const":
+                        return [[], {
+                            tag: "const",
+                            val: rval.operand.val,
+                        }];
+                }
+                return exhausted(rval.operand);
+            }
+            case "repeat":
+            case "ref":
+            case "ptr":
+            case "binary":
+            case "unary":
+                return todo();
+            case "adt":
+            case "call":
+            case "builtin":
+                return todo();
+        }
+        exhausted(rval);
+    }
+
+    private lowerTer(ter: mir.Ter): [lir.Stmt[], lir.Ter] {
+        const tk = ter.kind;
+        switch (tk.tag) {
+            case "unset":
+                return [[], this.ter({ tag: "error" })];
+            case "goto":
+                return [[], this.ter({ tag: "goto", target: tk.target })];
+            case "switch": {
+                const [s1, discr] = this.lowerOperand(tk.discr);
+                return [
+                    [...s1],
+                    this.ter({
+                        tag: "switch",
+                        discr,
+                        targets: tk.targets
+                            .map(({ target, value }) => ({ target, value })),
+                        otherwise: tk.otherwise,
+                    }),
+                ];
+            }
+            case "return":
+                return [[], this.ter({ tag: "return" })];
+            case "unreachable":
+                return [[], this.ter({ tag: "error" })];
+            case "drop":
+                return [[], this.ter({ tag: "error" })];
+        }
+        exhausted(tk);
+    }
+
+    private lowerOperand(operand: mir.Operand): [lir.Stmt[], lir.RVal] {
+        switch (operand.tag) {
+            case "error":
+                return [[], { tag: "error" }];
+            case "copy":
+            case "move":
+                return todo(operand.tag);
+            case "const":
+                return [[], { tag: "const", val: operand.val }];
+        }
+        exhausted(operand);
+    }
+
+    private stmt(kind: lir.StmtKind): lir.Stmt {
+        return { kind };
+    }
+
+    private ter(kind: lir.TerKind): lir.Ter {
+        return { kind };
+    }
+}
+
+function blockHasTarget(block: mir.Block, target: BlockId): boolean {
+    const tk = block.terminator.kind;
+    switch (tk.tag) {
+        case "unset":
+            return false;
+        case "goto":
+            return tk.target == target;
+        case "switch":
+            return tk.targets.some((st) => st.target === target) ||
+                tk.otherwise == target;
+        case "return":
+            return false;
+        case "unreachable":
+            return false;
+        case "drop":
+            return tk.target == target;
+    }
+    exhausted(tk);
+}
diff --git a/slige/compiler/middle/mod.ts b/slige/compiler/middle/mod.ts
index 353fac5..9002460 100644
--- a/slige/compiler/middle/mod.ts
+++ b/slige/compiler/middle/mod.ts
@@ -1,2 +1,6 @@
+export * as mir from "./mir.ts";
+export * as lir from "./lir.ts";
+export * as ast_lower from "./ast_lower.ts";
+export * as mir_lower from "./mir_lower.ts";
+
 export * from "./mir.ts";
-export * from "./ast_lower.ts";
diff --git a/slige/compiler/program.slg b/slige/compiler/program.slg
index ce8a38b..7905a9b 100644
--- a/slige/compiler/program.slg
+++ b/slige/compiler/program.slg
@@ -1,9 +1,15 @@
 
-#[builtin(Hello)]
-fn c_hello() -> int {}
+// #[builtin(Hello)]
+// fn c_hello() -> int {}
 
 fn main() {
-    c_hello();
+    let mut a = 2;
+    if true {
+        a = 3;
+    } else {
+
+    }
+    let b = a;
 }
 
 
diff --git a/slige/compiler/stringify/lir.ts b/slige/compiler/stringify/lir.ts
new file mode 100644
index 0000000..e8460ca
--- /dev/null
+++ b/slige/compiler/stringify/lir.ts
@@ -0,0 +1,127 @@
+import { BlockId, lir, mir } from "@slige/middle";
+import { Ctx, exhausted, IdMap, todo } from "@slige/common";
+import { Ty, tyToString } from "@slige/ty";
+
+export class LirFnStringifyer {
+    private blockIds = new IdMap<BlockId, number>();
+    private localIds = new IdMap<lir.LocalId, number>();
+
+    public constructor(
+        private ctx: Ctx,
+    ) {}
+
+    public fn(fn: lir.Fn): string {
+        for (
+            const [idx, id] of fn.blocks
+                .keys()
+                .toArray()
+                .entries()
+        ) {
+            this.blockIds.set(id, idx);
+        }
+        for (
+            const [idx, id] of fn.locals
+                .keys()
+                .toArray()
+                .entries()
+        ) {
+            this.localIds.set(id, idx);
+        }
+        const blocks = fn.blocks
+            .values()
+            .toArray()
+            .map((block) => this.block(block))
+            .join("\n");
+        return `fn ${fn.mirFn.label} {\n${blocks}\n}`
+            .replaceAll("#", "    ");
+    }
+
+    private block(block: lir.Block): string {
+        const id = this.blockIds.get(block.id);
+        return `#.b${id}: {\n${
+            [
+                ...block.stmts
+                    .map((stmt) => this.stmt(stmt)),
+                this.ter(block.ter),
+            ]
+                .join("\n")
+        }\n#}`;
+    }
+
+    private stmt(stmt: lir.Stmt): string {
+        const k = stmt.kind;
+        switch (k.tag) {
+            case "error":
+                return "##<error>;";
+            case "assign":
+                return `##${this.local(k.local)} = ${this.rval(k.rval)}`;
+        }
+        exhausted(k);
+    }
+
+    private ter(ter: lir.Ter): string {
+        const k = ter.kind;
+        switch (k.tag) {
+            case "error":
+                return "##<error>;";
+            case "goto":
+                return `##goto ${this.blockId(k.target)}`;
+            case "switch": {
+                const discr = this.rval(k.discr);
+                const targets = k.targets
+                    .map((target) =>
+                        `\n###${target.value} => ${this.blockId(target.target)}`
+                    )
+                    .join("");
+                const otherwise = this.blockId(k.otherwise);
+                return `##switch ${discr}${targets}\n###_ => ${otherwise}`;
+            }
+            case "return":
+                return `##return;`;
+        }
+        exhausted(k);
+    }
+
+    private rval(rval: lir.RVal): string {
+        switch (rval.tag) {
+            case "error":
+                return "<error>";
+            case "phi":
+                return `phi [${
+                    rval.sources
+                        .map((src) =>
+                            `(${this.blockId(src.branch)}, ${
+                                this.local(src.local)
+                            })`
+                        )
+                        .join(",")
+                }]`;
+            case "use":
+                return this.local(rval.local);
+            case "const":
+                return `${this.constVal(rval.val)}`;
+        }
+    }
+
+    private constVal(val: mir.Const): string {
+        switch (val.tag) {
+            case "null":
+                return `null`;
+            case "int":
+                return `${val.value}`;
+            case "str":
+                return `"${val.value}"`;
+            case "fn":
+                return `${val.item.ident.text}`;
+        }
+        exhausted(val);
+    }
+
+    private blockId(id: BlockId): string {
+        return `.b${this.blockIds.get(id)!}`;
+    }
+
+    private local(local: lir.LocalId): string {
+        return `%${this.localIds.get(local)!}`;
+    }
+}
diff --git a/slige/compiler/stringify/mod.ts b/slige/compiler/stringify/mod.ts
index 28b54e5..eb237de 100644
--- a/slige/compiler/stringify/mod.ts
+++ b/slige/compiler/stringify/mod.ts
@@ -1,2 +1,3 @@
 export * from "./hir.ts";
 export * from "./mir.ts";
+export * from "./lir.ts";