diff --git a/compiler/compiler.ts b/compiler/compiler.ts
index 6d85a1b..d2714b0 100644
--- a/compiler/compiler.ts
+++ b/compiler/compiler.ts
@@ -10,11 +10,13 @@ import { FnNamesMap, Lowerer } from "./lowerer.ts";
 import { Parser } from "./parser.ts";
 import { Resolver } from "./resolver.ts";
 import { AstVisitor, VisitRes, visitStmts } from "./ast_visitor.ts";
-
-import * as path from "jsr:@std/path";
 import { Pos } from "./token.ts";
 import { ArrayLiteralDesugarer } from "./desugar/array_literal.ts";
 
+import * as path from "jsr:@std/path";
+import { AstLowerer } from "./middle/lower_ast.ts";
+import { printMir } from "./middle/mir.ts";
+
 export type CompileResult = {
     program: number[];
     fnNames: FnNamesMap;
@@ -29,28 +31,32 @@ export class Compiler {
     }
 
     public async compile(): Promise<CompileResult> {
-        const mod = new ModTree(
+        const { ast } = new ModTree(
             this.startFilePath,
             this.astCreator,
             this.reporter,
         ).resolve();
 
-        new SpecialLoopDesugarer(this.astCreator).desugar(mod.ast);
-        new ArrayLiteralDesugarer(this.astCreator).desugar(mod.ast);
-        new StructLiteralDesugarer(this.astCreator).desugar(mod.ast);
+        new SpecialLoopDesugarer(this.astCreator).desugar(ast);
+        new ArrayLiteralDesugarer(this.astCreator).desugar(ast);
+        new StructLiteralDesugarer(this.astCreator).desugar(ast);
 
-        new Resolver(this.reporter).resolve(mod.ast);
+        new Resolver(this.reporter).resolve(ast);
 
-        new CompoundAssignDesugarer(this.astCreator).desugar(mod.ast);
+        new CompoundAssignDesugarer(this.astCreator).desugar(ast);
 
-        new Checker(this.reporter).check(mod.ast);
+        new Checker(this.reporter).check(ast);
+
+        const mir = new AstLowerer(ast).lower();
+
+        printMir(mir);
 
         if (this.reporter.errorOccured()) {
             console.error("Errors occurred, stopping compilation.");
             Deno.exit(1);
         }
 
-        const { monoFns, callMap } = new Monomorphizer(mod.ast).monomorphize();
+        const { monoFns, callMap } = new Monomorphizer(ast).monomorphize();
 
         const lastPos = await lastPosInTextFile(this.startFilePath);
 
diff --git a/compiler/middle/lower_ast.ts b/compiler/middle/lower_ast.ts
new file mode 100644
index 0000000..b38513f
--- /dev/null
+++ b/compiler/middle/lower_ast.ts
@@ -0,0 +1,469 @@
+import * as Ast from "../ast.ts";
+import { AllFnsCollector } from "../mono.ts";
+import { VType, vtypesEqual } from "../vtype.ts";
+import {
+    Block,
+    BlockId,
+    Fn,
+    Local,
+    LocalId,
+    Mir,
+    Op,
+    OpKind,
+    Ter,
+    TerKind,
+} from "./mir.ts";
+
+export class AstLowerer {
+    public constructor(private ast: Ast.Stmt[]) {}
+
+    public lower(): Mir {
+        const fnAsts = new AllFnsCollector().collect(this.ast).values();
+        const fns = fnAsts
+            .map((fnAst) => new FnAstLowerer(fnAst).lower())
+            .toArray();
+        return { fns };
+    }
+}
+
+class LocalAllocator {
+    private locals: Local[] = [];
+
+    public alloc(vtype: VType): LocalId {
+        const id = this.locals.length;
+        this.locals.push({ id, vtype });
+        return id;
+    }
+
+    public finish(): Local[] {
+        return this.locals;
+    }
+}
+
+class FnAstLowerer {
+    private locals = new LocalAllocator();
+    private blockIdCounter = 0;
+    private currentBlockId = 0;
+    private blocks = new Map<BlockId, Block>();
+
+    private fnParamIndexLocals = new Map<number, LocalId>();
+    private letStmtIdLocals = new Map<number, LocalId>();
+
+    private breakStack: { local: LocalId; block: BlockId }[] = [];
+
+    public constructor(private ast: Ast.Stmt) {}
+
+    public lower(): Fn {
+        const stmt = this.ast;
+        if (stmt.kind.type !== "fn") {
+            throw new Error();
+        }
+        const vtype = stmt.kind.vtype;
+        if (vtype?.type !== "fn") {
+            throw new Error();
+        }
+
+        this.locals.alloc(stmt.kind.vtype!);
+        for (const param of stmt.kind.params) {
+            const id = this.locals.alloc(param.vtype!);
+            this.fnParamIndexLocals.set(param.index!, id);
+        }
+
+        this.pushBlock("entry");
+        this.lowerBlockExpr(stmt.kind.body);
+        this.pushBlock("exit");
+
+        const locals = this.locals.finish();
+        const blocks = this.blocks.values().toArray();
+        return { stmt, locals, blocks };
+    }
+
+    private lowerStmt(stmt: Ast.Stmt) {
+        switch (stmt.kind.type) {
+            case "error":
+            case "mod_block":
+            case "mod_file":
+            case "mod":
+                break;
+            case "break": {
+                const { local, block } = this.breakStack.at(-1)!;
+                if (stmt.kind.expr) {
+                    const val = this.lowerExpr(stmt.kind.expr);
+                    this.addOp({ type: "assign", dst: local, src: val });
+                } else {
+                    this.addOp({ type: "assign_null", dst: local });
+                }
+                this.setTer({ type: "jump", target: block });
+                this.pushBlock();
+                return;
+            }
+            case "return":
+                break;
+            case "fn":
+                // nothing
+                return;
+            case "let":
+                this.lowerLetStmt(stmt);
+                return;
+            case "type_alias":
+                break;
+            case "assign":
+                return this.lowerAssign(stmt);
+            case "expr": {
+                const val = this.lowerExpr(stmt.kind.expr);
+                this.addOp({ type: "drop", val });
+                return;
+            }
+        }
+        throw new Error(`statement type '${stmt.kind.type}' not covered`);
+    }
+
+    private lowerAssign(stmt: Ast.Stmt) {
+        if (stmt.kind.type !== "assign") {
+            throw new Error();
+        }
+        if (stmt.kind.assignType !== "=") {
+            throw new Error("incomplete desugar");
+        }
+        const src = this.lowerExpr(stmt.kind.value);
+        const s = stmt.kind.subject;
+        switch (s.kind.type) {
+            case "field": {
+                const subject = this.lowerExpr(s.kind.subject);
+                const ident = s.kind.ident;
+                this.addOp({ type: "assign_field", subject, ident, src });
+                return;
+            }
+            case "index": {
+                const subject = this.lowerExpr(s.kind.subject);
+                const index = this.lowerExpr(s.kind.value);
+                this.addOp({ type: "assign_field", subject, index, src });
+                return;
+            }
+            case "sym": {
+                const sym = s.kind.sym;
+                switch (sym.type) {
+                    case "let": {
+                        const dst = this.letStmtIdLocals.get(sym.stmt.id)!;
+                        this.addOp({ type: "assign", dst, src });
+                        return;
+                    }
+                    case "fn_param": {
+                        const dst = this.fnParamIndexLocals.get(
+                            sym.param.index!,
+                        )!;
+                        this.addOp({ type: "assign", dst, src });
+                        return;
+                    }
+                }
+                throw new Error(`symbol type '${sym.type}' not covered`);
+            }
+            default:
+                throw new Error();
+        }
+    }
+
+    private lowerLetStmt(stmt: Ast.Stmt) {
+        if (stmt.kind.type !== "let") {
+            throw new Error();
+        }
+        const src = this.lowerExpr(stmt.kind.value);
+        const dst = this.locals.alloc(stmt.kind.param.vtype!);
+        this.addOp({ type: "assign", dst, src });
+        this.letStmtIdLocals.set(stmt.id, dst);
+    }
+
+    private lowerExpr(expr: Ast.Expr): LocalId {
+        switch (expr.kind.type) {
+            case "error": {
+                const dst = this.locals.alloc({ type: "error" });
+                this.addOp({ type: "assign_error", dst });
+                return dst;
+            }
+            case "null": {
+                const dst = this.locals.alloc({ type: "null" });
+                this.addOp({ type: "assign_null", dst });
+                return dst;
+            }
+            case "bool": {
+                const val = expr.kind.value;
+                const dst = this.locals.alloc({ type: "bool" });
+                this.addOp({ type: "assign_bool", dst, val });
+                return dst;
+            }
+            case "int": {
+                const val = expr.kind.value;
+                const dst = this.locals.alloc({ type: "int" });
+                this.addOp({ type: "assign_int", dst, val });
+                return dst;
+            }
+            case "string": {
+                const val = expr.kind.value;
+                const dst = this.locals.alloc({ type: "string" });
+                this.addOp({ type: "assign_string", dst, val });
+                return dst;
+            }
+            case "ident":
+                throw new Error("should've been resolved");
+            case "sym":
+                return this.lowerSymExpr(expr);
+            case "group":
+                return this.lowerExpr(expr.kind.expr);
+            case "array":
+                throw new Error("incomplete desugar");
+            case "struct":
+                throw new Error("incomplete desugar");
+            case "field":
+                return this.lowerFieldExpr(expr);
+            case "index":
+                return this.lowerIndexExpr(expr);
+            case "call":
+                return this.lowerCallExpr(expr);
+            case "path":
+            case "etype_args":
+            case "unary":
+                break;
+            case "binary":
+                return this.lowerBinaryExpr(expr);
+            case "if":
+                return this.lowerIfExpr(expr);
+            case "loop":
+                return this.lowerLoopExpr(expr);
+            case "block":
+                return this.lowerBlockExpr(expr);
+            case "while":
+            case "for_in":
+            case "for":
+                throw new Error("incomplete desugar");
+        }
+        throw new Error(`expression type '${expr.kind.type}' not covered`);
+    }
+
+    private lowerSymExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "sym") {
+            throw new Error();
+        }
+        const sym = expr.kind.sym;
+        switch (sym.type) {
+            case "let":
+                return this.letStmtIdLocals.get(sym.stmt.id)!;
+            case "let_static":
+            case "type_alias":
+                break;
+            case "fn": {
+                const stmt = sym.stmt;
+                if (sym.stmt.kind.type !== "fn") {
+                    throw new Error();
+                }
+                const dst = this.locals.alloc(sym.stmt.kind.vtype!);
+                this.addOp({ type: "assign_fn", dst, stmt });
+                return dst;
+            }
+            case "fn_param": {
+                return this.fnParamIndexLocals.get(sym.param.index!)!;
+            }
+            case "closure":
+            case "generic":
+            case "mod":
+        }
+        throw new Error(`symbol type '${sym.type}' not covered`);
+    }
+
+    private lowerFieldExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "field") {
+            throw new Error();
+        }
+        const ident = expr.kind.ident;
+        const subject = this.lowerExpr(expr.kind.subject);
+
+        const subjectVType = expr.kind.subject.vtype!;
+        if (subjectVType.type !== "struct") {
+            throw new Error();
+        }
+        const fieldVType = subjectVType.fields.find((field) =>
+            field.ident === ident
+        );
+        if (fieldVType === undefined) {
+            throw new Error();
+        }
+
+        const dst = this.locals.alloc(fieldVType.vtype);
+        this.addOp({ type: "field", dst, subject, ident });
+        return dst;
+    }
+
+    private lowerIndexExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "index") {
+            throw new Error();
+        }
+        const subject = this.lowerExpr(expr.kind.subject);
+        const index = this.lowerExpr(expr.kind.value);
+
+        const dstVType = ((): VType => {
+            const outer = expr.kind.subject.vtype!;
+            if (outer.type === "array") {
+                return outer.inner;
+            }
+            if (outer.type === "string") {
+                return { type: "int" };
+            }
+            throw new Error();
+        })();
+
+        const dst = this.locals.alloc(dstVType);
+        this.addOp({ type: "index", dst, subject, index });
+        return dst;
+    }
+
+    private lowerCallExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "call") {
+            throw new Error();
+        }
+
+        const args = expr.kind.args.map((arg) => this.lowerExpr(arg));
+
+        const subject = this.lowerExpr(expr.kind.subject);
+
+        const subjectVType = expr.kind.subject.vtype!;
+        if (subjectVType.type !== "fn") {
+            throw new Error();
+        }
+
+        const dst = this.locals.alloc(subjectVType.returnType);
+        this.addOp({ type: "call_val", dst, subject, args });
+        return dst;
+    }
+
+    private lowerBinaryExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "binary") {
+            throw new Error();
+        }
+        const leftVType = expr.kind.left.vtype!;
+        const rightVType = expr.kind.right.vtype!;
+        if (!vtypesEqual(leftVType, rightVType)) {
+            throw new Error();
+        }
+        //const vtype = leftVType.type === "error" && rightVType || leftVType;
+
+        const binaryType = expr.kind.binaryType;
+        const left = this.lowerExpr(expr.kind.left);
+        const right = this.lowerExpr(expr.kind.right);
+
+        const dst = this.locals.alloc(expr.vtype!);
+
+        this.addOp({ type: "binary", binaryType, dst, left, right });
+        return dst;
+
+        //throw new Error(
+        //    `binary vtype '${vtypeToString(leftVType)}' not covered`,
+        //);
+    }
+
+    private lowerIfExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "if") {
+            throw new Error();
+        }
+        const condBlock = this.currentBlock();
+        const cond = this.lowerExpr(expr.kind.cond);
+        const end = this.reserveBlock();
+
+        const val = this.locals.alloc(expr.vtype!);
+
+        const truthy = this.pushBlock();
+        const truthyVal = this.lowerExpr(expr.kind.truthy);
+        this.addOp({ type: "assign", dst: val, src: truthyVal });
+        this.setTer({ type: "jump", target: end });
+
+        if (expr.kind.falsy) {
+            const falsy = this.pushBlock();
+            const falsyVal = this.lowerExpr(expr.kind.falsy);
+            this.addOp({ type: "assign", dst: val, src: falsyVal });
+            this.setTer({ type: "jump", target: end });
+
+            this.setTerOn(condBlock, { type: "if", cond, truthy, falsy });
+        } else {
+            this.setTerOn(condBlock, { type: "if", cond, truthy, falsy: end });
+        }
+
+        return val;
+    }
+
+    private lowerLoopExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "loop") {
+            throw new Error();
+        }
+
+        const val = this.locals.alloc(expr.vtype!);
+        const breakBlock = this.reserveBlock();
+        this.breakStack.push({ local: val, block: breakBlock });
+
+        const body = this.pushBlock();
+        this.setTer({ type: "jump", target: body });
+
+        this.lowerExpr(expr.kind.body);
+        this.setTer({ type: "jump", target: body });
+
+        this.breakStack.pop();
+
+        this.pushBlockWithId(breakBlock);
+        return val;
+    }
+
+    private lowerBlockExpr(expr: Ast.Expr): LocalId {
+        if (expr.kind.type !== "block") {
+            throw new Error();
+        }
+
+        for (const stmt of expr.kind.stmts) {
+            this.lowerStmt(stmt);
+        }
+        if (expr.kind.expr) {
+            return this.lowerExpr(expr.kind.expr);
+        } else {
+            const local = this.locals.alloc({ type: "null" });
+            this.addOp({ type: "assign_null", dst: local });
+            return local;
+        }
+    }
+
+    private addOp(kind: OpKind) {
+        this.blocks.get(this.currentBlockId)!.ops.push({ kind });
+    }
+
+    private addOpOn(blockId: BlockId, kind: OpKind) {
+        this.blocks.get(blockId)!.ops.push({ kind });
+    }
+
+    private setTer(kind: TerKind) {
+        this.blocks.get(this.currentBlockId)!.ter = { kind };
+    }
+
+    private setTerOn(blockId: BlockId, kind: TerKind) {
+        this.blocks.get(blockId)!.ter = { kind };
+    }
+
+    private currentBlock(): BlockId {
+        return this.currentBlockId;
+    }
+
+    private reserveBlock(): BlockId {
+        const id = this.blockIdCounter;
+        this.blockIdCounter += 1;
+        return id;
+    }
+
+    private pushBlock(label?: string): BlockId {
+        const id = this.blockIdCounter;
+        this.blockIdCounter += 1;
+        const ter: Ter = { kind: { type: "error" } };
+        this.blocks.set(id, { id, ops: [], ter, label });
+        return id;
+    }
+
+    private pushBlockWithId(id: BlockId): BlockId {
+        this.blockIdCounter += 1;
+        const ter: Ter = { kind: { type: "error" } };
+        this.blocks.set(id, { id, ops: [], ter });
+        return id;
+    }
+}
diff --git a/compiler/middle/mir.ts b/compiler/middle/mir.ts
new file mode 100644
index 0000000..725e3bd
--- /dev/null
+++ b/compiler/middle/mir.ts
@@ -0,0 +1,152 @@
+import { BinaryType, Stmt } from "../ast.ts";
+import { VType, vtypeToString } from "../vtype.ts";
+
+export type Mir = {
+    fns: Fn[];
+};
+
+export type Fn = {
+    stmt: Stmt;
+    locals: Local[];
+    blocks: Block[];
+};
+
+export type LocalId = number;
+
+export type Local = {
+    id: LocalId;
+    vtype: VType;
+};
+
+export type BlockId = number;
+
+export type Block = {
+    id: BlockId;
+    ops: Op[];
+    ter: Ter;
+    label?: string;
+};
+
+export type Op = {
+    kind: OpKind;
+};
+
+type L = LocalId;
+
+export type OpKind =
+    | { type: "error" }
+    | { type: "return" }
+    | { type: "drop"; val: L }
+    | { type: "assign"; dst: L; src: L }
+    | { type: "assign_error"; dst: L }
+    | { type: "assign_null"; dst: L }
+    | { type: "assign_bool"; dst: L; val: boolean }
+    | { type: "assign_int"; dst: L; val: number }
+    | { type: "assign_string"; dst: L; val: string }
+    | { type: "assign_fn"; dst: L; stmt: Stmt }
+    | { type: "field"; dst: L; subject: L; ident: string }
+    | { type: "assign_field"; subject: L; ident: string; src: L }
+    | { type: "index"; dst: L; subject: L; index: number }
+    | { type: "assign_field"; subject: L; index: L; src: L }
+    | { type: "call_val"; dst: L; subject: L; args: L[] }
+    | { type: "binary"; binaryType: BinaryType; dst: L; left: L; right: L };
+
+export type Ter = {
+    kind: TerKind;
+};
+
+export type TerKind =
+    | { type: "error" }
+    | { type: "jump"; target: BlockId }
+    | { type: "if"; cond: L; truthy: BlockId; falsy: BlockId };
+
+export function printMir(mir: Mir) {
+    for (const fn of mir.fns) {
+        const stmt = fn.stmt;
+        if (stmt.kind.type !== "fn") {
+            throw new Error();
+        }
+        const name = stmt.kind.ident;
+
+        const vtype = stmt.kind.vtype;
+        if (vtype?.type !== "fn") {
+            throw new Error();
+        }
+        const generics = vtype.genericParams
+            ?.map(({ ident }) => `${ident}`).join(", ") ?? "";
+        const params = vtype.params
+            .map(({ vtype }, i) =>
+                `_${fn.locals[i + 1].id}: ${vtypeToString(vtype)}`
+            )
+            .join(", ");
+        const returnType = vtypeToString(vtype.returnType);
+        console.log(`${name}${generics}(${params}) -> ${returnType}:`);
+        for (const { id, vtype } of fn.locals) {
+            console.log(`    let _${id}: ${vtypeToString(vtype)};`);
+        }
+        for (const block of fn.blocks) {
+            console.log(`.${block.label ?? block.id}:`);
+            for (const op of block.ops) {
+                const k = op.kind;
+                switch (k.type) {
+                    case "error":
+                        console.log(`    <error>;`);
+                        break;
+                    case "return":
+                        console.log(`    return;`);
+                        break;
+                    case "drop":
+                        console.log(`    drop _${k.val};`);
+                        break;
+                    case "assign":
+                        console.log(`    _${k.dst} = _${k.src};`);
+                        break;
+                    case "assign_error":
+                        console.log(`    _${k.dst} = <error>;`);
+                        break;
+                    case "assign_null":
+                        console.log(`    _${k.dst} = null;`);
+                        break;
+                    case "assign_bool":
+                        console.log(`    _${k.dst} = ${k.val};`);
+                        break;
+                    case "assign_int":
+                        console.log(`    _${k.dst} = ${k.val};`);
+                        break;
+                    case "assign_string":
+                        console.log(`    _${k.dst} = "${k.val}";`);
+                        break;
+                    case "assign_fn": {
+                        const stmt = k.stmt;
+                        if (stmt.kind.type !== "fn") {
+                            throw new Error();
+                        }
+                        console.log(`    _${k.dst} = ${stmt.kind.ident};`);
+                        break;
+                    }
+                    case "field":
+                        console.log(
+                            `    _${k.dst} = _${k.subject}.${k.ident};`,
+                        );
+                        break;
+                    case "index":
+                        console.log(
+                            `    _${k.dst} = _${k.subject}[_${k.index}];`,
+                        );
+                        break;
+                    case "call_val": {
+                        const args = k.args.map((arg) => `_${arg}`).join(", ");
+                        console.log(`    _${k.dst} = _${k.subject}(${args});`);
+                        break;
+                    }
+                    case "binary": {
+                        console.log(
+                            `    _${k.dst} = _${k.left} ${k.binaryType} _${k.right};`,
+                        );
+                        break;
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/compiler/mono.ts b/compiler/mono.ts
index 9ccc45b..45a1cb3 100644
--- a/compiler/mono.ts
+++ b/compiler/mono.ts
@@ -181,7 +181,7 @@ function vtypeNameGenPart(vtype: VType): string {
     }
 }
 
-class AllFnsCollector implements AstVisitor {
+export class AllFnsCollector implements AstVisitor {
     private allFns = new Map<number, Stmt>();
 
     public collect(ast: Stmt[]): Map<number, Stmt> {
diff --git a/compiler/vtype.ts b/compiler/vtype.ts
index bf432d1..c0bbe1b 100644
--- a/compiler/vtype.ts
+++ b/compiler/vtype.ts
@@ -130,7 +130,7 @@ export function vtypeToString(vtype: VType): string {
             `${param.ident}: ${vtypeToString(param.vtype)}`
         )
             .join(", ");
-        return `fn (${paramString}) -> ${vtypeToString(vtype.returnType)}`;
+        return `fn(${paramString}) -> ${vtypeToString(vtype.returnType)}`;
     }
     if (vtype.type === "generic") {
         return `generic`;