diff --git a/compiler/ast.ts b/compiler/ast.ts
index 46f030d..9c3a51d 100644
--- a/compiler/ast.ts
+++ b/compiler/ast.ts
@@ -63,6 +63,9 @@ export type ExprKind =
         sym: Sym;
     }
     | { type: "group"; expr: Expr }
+    | { type: "ref"; subject: Expr }
+    | { type: "ref_mut"; subject: Expr }
+    | { type: "deref"; subject: Expr }
     | { type: "array"; exprs: Expr[] }
     | { type: "struct"; fields: Field[] }
     | { type: "field"; subject: Expr; ident: string }
@@ -117,6 +120,7 @@ export type Param = {
     id: number;
     index?: number;
     ident: string;
+    mut: boolean;
     etype?: EType;
     pos: Pos;
     sym?: Sym;
@@ -157,7 +161,11 @@ export type ETypeKind =
         ident: string;
         sym: Sym;
     }
-    | { type: "array"; inner: EType }
+    | { type: "ref"; subject: EType }
+    | { type: "ref_mut"; subject: EType }
+    | { type: "ptr"; subject: EType }
+    | { type: "ptr_mut"; subject: EType }
+    | { type: "array"; subject: EType }
     | { type: "struct"; fields: Param[] }
     | { type: "type_of"; expr: Expr };
 
@@ -227,3 +235,7 @@ export class AnnoView {
         return anno;
     }
 }
+
+export function forceType(v: unknown): { type: string } {
+    return v as { type: string };
+}
diff --git a/compiler/ast_visitor.ts b/compiler/ast_visitor.ts
index ba6c8ac..578e23d 100644
--- a/compiler/ast_visitor.ts
+++ b/compiler/ast_visitor.ts
@@ -22,6 +22,9 @@ export interface AstVisitor<Args extends unknown[] = []> {
     visitStringExpr?(expr: Expr, ...args: Args): VisitRes;
     visitIdentExpr?(expr: Expr, ...args: Args): VisitRes;
     visitGroupExpr?(expr: Expr, ...args: Args): VisitRes;
+    visitRefExpr?(expr: Expr, ...args: Args): VisitRes;
+    visitRefMutExpr?(expr: Expr, ...args: Args): VisitRes;
+    visitDerefExpr?(expr: Expr, ...args: Args): VisitRes;
     visitArrayExpr?(expr: Expr, ...args: Args): VisitRes;
     visitStructExpr?(expr: Expr, ...args: Args): VisitRes;
     visitFieldExpr?(expr: Expr, ...args: Args): VisitRes;
@@ -50,6 +53,10 @@ export interface AstVisitor<Args extends unknown[] = []> {
     visitStringEType?(etype: EType, ...args: Args): VisitRes;
     visitIdentEType?(etype: EType, ...args: Args): VisitRes;
     visitSymEType?(etype: EType, ...args: Args): VisitRes;
+    visitRefEType?(etype: EType, ...args: Args): VisitRes;
+    visitRefMutEType?(etype: EType, ...args: Args): VisitRes;
+    visitPtrEType?(etype: EType, ...args: Args): VisitRes;
+    visitPtrMutEType?(etype: EType, ...args: Args): VisitRes;
     visitArrayEType?(etype: EType, ...args: Args): VisitRes;
     visitStructEType?(etype: EType, ...args: Args): VisitRes;
     visitTypeOfEType?(etype: EType, ...args: Args): VisitRes;
@@ -152,6 +159,18 @@ export function visitExpr<Args extends unknown[] = []>(
             if (v.visitGroupExpr?.(expr, ...args) == "stop") return;
             visitExpr(expr.kind.expr, v, ...args);
             break;
+        case "ref":
+            if (v.visitRefExpr?.(expr, ...args) == "stop") return;
+            visitExpr(expr.kind.subject, v, ...args);
+            break;
+        case "ref_mut":
+            if (v.visitRefMutExpr?.(expr, ...args) == "stop") return;
+            visitExpr(expr.kind.subject, v, ...args);
+            break;
+        case "deref":
+            if (v.visitDerefExpr?.(expr, ...args) == "stop") return;
+            visitExpr(expr.kind.subject, v, ...args);
+            break;
         case "field":
             if (v.visitFieldExpr?.(expr, ...args) == "stop") return;
             visitExpr(expr.kind.subject, v, ...args);
@@ -289,9 +308,25 @@ export function visitEType<Args extends unknown[] = []>(
         case "sym":
             if (v.visitSymEType?.(etype, ...args) == "stop") return;
             break;
+        case "ref":
+            if (v.visitRefEType?.(etype, ...args) == "stop") return;
+            visitEType(etype.kind.subject, v, ...args);
+            break;
+        case "ref_mut":
+            if (v.visitRefMutEType?.(etype, ...args) == "stop") return;
+            visitEType(etype.kind.subject, v, ...args);
+            break;
+        case "ptr":
+            if (v.visitPtrEType?.(etype, ...args) == "stop") return;
+            visitEType(etype.kind.subject, v, ...args);
+            break;
+        case "ptr_mut":
+            if (v.visitPtrMutEType?.(etype, ...args) == "stop") return;
+            visitEType(etype.kind.subject, v, ...args);
+            break;
         case "array":
             if (v.visitArrayEType?.(etype, ...args) == "stop") return;
-            if (etype.kind.inner) visitEType(etype.kind.inner, v, ...args);
+            visitEType(etype.kind.subject, v, ...args);
             break;
         case "struct":
             if (v.visitStructEType?.(etype, ...args) == "stop") return;
diff --git a/compiler/checker.ts b/compiler/checker.ts
index 703644d..132eb25 100644
--- a/compiler/checker.ts
+++ b/compiler/checker.ts
@@ -1,4 +1,4 @@
-import { AnnoView, EType, Expr, Stmt, Sym } from "./ast.ts";
+import { AnnoView, EType, Expr, forceType, Stmt, Sym } from "./ast.ts";
 import { printStackTrace, Reporter } from "./info.ts";
 import { Pos } from "./token.ts";
 import {
@@ -286,7 +286,7 @@ export class Checker {
                 }
                 if (
                     subject.type == "array" &&
-                    !vtypesEqual(subject.inner, value)
+                    !vtypesEqual(subject.subject, value)
                 ) {
                     this.report(
                         `cannot assign incompatible type to array ` +
@@ -348,6 +348,12 @@ export class Checker {
                     return { type: "string" };
                 case "group":
                     return this.checkExpr(expr.kind.expr);
+                case "ref":
+                    return this.checkRefExpr(expr);
+                case "ref_mut":
+                    return this.checkRefMutExpr(expr);
+                case "deref":
+                    return this.checkDerefExpr(expr);
                 case "array":
                     throw new Error("should have been desugared");
                 case "struct":
@@ -421,6 +427,89 @@ export class Checker {
         }
     }
 
+    public checkRefExpr(expr: Expr): VType {
+        if (expr.kind.type !== "ref") {
+            throw new Error();
+        }
+        const subject = this.checkExpr(expr.kind.subject);
+        if (expr.kind.subject.kind.type === "sym") {
+            const sym = expr.kind.subject.kind.sym;
+            if (sym.type === "let" || sym.type === "fn_param") {
+                return { type: "ref", subject };
+            }
+            this.report(
+                `taking reference to symbol type '${sym.type}' not supported`,
+                expr.pos,
+            );
+            return { type: "error" };
+        }
+        this.report(
+            `taking reference to expression type '${
+                forceType(expr.kind.subject.kind).type
+            }' not supported`,
+            expr.pos,
+        );
+        return { type: "error" };
+    }
+
+    public checkRefMutExpr(expr: Expr): VType {
+        if (expr.kind.type !== "ref_mut") {
+            throw new Error();
+        }
+        const subject = this.checkExpr(expr.kind.subject);
+        if (expr.kind.subject.kind.type === "sym") {
+            const sym = expr.kind.subject.kind.sym;
+            if (sym.type === "let" || sym.type === "fn_param") {
+                if (!sym.param.mut) {
+                    this.report(
+                        `symbol '${sym.ident}' it not declared mutable`,
+                        expr.pos,
+                    );
+                    this.reporter.addNote({
+                        reporter: "checker",
+                        msg: "symbol defined here",
+                        pos: sym.param.pos,
+                    });
+                    return { type: "error" };
+                }
+                return { type: "ref_mut", subject };
+            }
+            this.report(
+                `taking reference to symbol type '${sym.type}' not supported`,
+                expr.pos,
+            );
+            return { type: "error" };
+        }
+        this.report(
+            `taking mutable reference to expression type '${
+                forceType(expr.kind.subject.kind).type
+            }' not supported`,
+            expr.pos,
+        );
+        return { type: "error" };
+    }
+    public checkDerefExpr(expr: Expr): VType {
+        if (expr.kind.type !== "deref") {
+            throw new Error();
+        }
+        const subject = this.checkExpr(expr.kind.subject);
+        switch (subject.type) {
+            case "ref":
+                return subject.subject;
+            case "ref_mut":
+                return subject.subject;
+            case "ptr":
+                return subject.subject;
+            case "ptr_mut":
+                return subject.subject;
+        }
+        this.report(
+            `dereferenced type is neither a reference nor a pointer`,
+            expr.pos,
+        );
+        return { type: "error" };
+    }
+
     public checkStructExpr(expr: Expr): VType {
         if (expr.kind.type !== "struct") {
             throw new Error();
@@ -472,7 +561,7 @@ export class Checker {
             return { type: "error" };
         }
         if (subject.type === "array") {
-            return subject.inner;
+            return subject.subject;
         }
         return { type: "int" };
     }
@@ -653,7 +742,7 @@ export class Checker {
             return { a, b };
         }
         if (a.type === "array" && b.type === "array") {
-            return this.reduceToSignificant(a.inner, b.inner);
+            return this.reduceToSignificant(a.subject, b.subject);
         }
         if (a.type === "generic" && b.type === "generic") {
             return { a, b };
@@ -670,8 +759,13 @@ export class Checker {
             case "int":
             case "bool":
                 return false;
+            case "ref":
+            case "ref_mut":
+            case "ptr":
+            case "ptr_mut":
+                return this.vtypeContainsGeneric(vtype.subject);
             case "array":
-                return this.vtypeContainsGeneric(vtype.inner);
+                return this.vtypeContainsGeneric(vtype.subject);
             case "struct":
                 return vtype.fields.some((field) =>
                     this.vtypeContainsGeneric(field.vtype)
@@ -749,10 +843,14 @@ export class Checker {
             case "int":
             case "bool":
                 return vtype;
+            case "ref":
+            case "ref_mut":
+            case "ptr":
+            case "ptr_mut":
             case "array":
                 return {
-                    type: "array",
-                    inner: this.concretizeVType(vtype.inner, generics),
+                    type: vtype.type,
+                    subject: this.concretizeVType(vtype.subject, generics),
                 };
             case "struct":
                 return {
@@ -994,9 +1092,25 @@ export class Checker {
             this.report(`sym type '${etype.kind.sym.type}' used as type`, pos);
             return { type: "error" };
         }
+        if (etype.kind.type === "ref") {
+            const subject = this.checkEType(etype.kind.subject);
+            return { type: "ref", subject };
+        }
+        if (etype.kind.type === "ref_mut") {
+            const subject = this.checkEType(etype.kind.subject);
+            return { type: "ref", subject };
+        }
+        if (etype.kind.type === "ptr") {
+            const subject = this.checkEType(etype.kind.subject);
+            return { type: "ptr", subject };
+        }
+        if (etype.kind.type === "ptr_mut") {
+            const subject = this.checkEType(etype.kind.subject);
+            return { type: "ptr_mut", subject };
+        }
         if (etype.kind.type === "array") {
-            const inner = this.checkEType(etype.kind.inner);
-            return { type: "array", inner };
+            const subject = this.checkEType(etype.kind.subject);
+            return { type: "array", subject };
         }
         if (etype.kind.type === "struct") {
             const noTypeTest = etype.kind.fields.reduce(
diff --git a/compiler/compiler.ts b/compiler/compiler.ts
index 22f1783..dd3a6f3 100644
--- a/compiler/compiler.ts
+++ b/compiler/compiler.ts
@@ -21,7 +21,8 @@ import {
     eliminateOnlyChildsBlocks,
     eliminateUnreachableBlocks,
 } from "./middle/elim_blocks.ts";
-import { eliminateTransientVals } from "./middle/elim_transient_vals.ts";
+import { checkBorrows } from "./middle/borrow_checker.ts";
+import { makeMoveCopyExplicit } from "./middle/explicit_move_copy.ts";
 
 export type CompileResult = {
     program: number[];
@@ -53,44 +54,52 @@ export class Compiler {
 
         new Checker(this.reporter).check(ast);
 
-        const mir = lowerAst(ast);
+        //const mir = lowerAst(ast);
+        //
+        //console.log("Before optimizations:");
+        //printMir(mir);
 
-        console.log("Before optimizations:");
-        printMir(mir);
-
-        const mirHistory = [mirOpCount(mir)];
-        for (let i = 0; i < 1; ++i) {
-            eliminateUnusedLocals(mir, this.reporter, mirHistory.length === 1);
-            eliminateOnlyChildsBlocks(mir);
-            eliminateUnreachableBlocks(mir);
-            eliminateTransientVals(mir);
-
-            const opCount = mirOpCount(mir);
-            const histOccurence = mirHistory
-                .filter((v) => v === opCount).length;
-            if (histOccurence >= 2) {
-                break;
-            }
-            mirHistory.push(opCount);
-        }
-
-        console.log("After optimizations:");
-        printMir(mir);
+        //const mirHistory = [mirOpCount(mir)];
+        //for (let i = 0; i < 1; ++i) {
+        //    eliminateUnusedLocals(mir, this.reporter, mirHistory.length === 1);
+        //    eliminateOnlyChildsBlocks(mir);
+        //    eliminateUnreachableBlocks(mir);
+        //    eliminateTransientVals(mir);
+        //
+        //    const opCount = mirOpCount(mir);
+        //    const histOccurence = mirHistory
+        //        .filter((v) => v === opCount).length;
+        //    if (histOccurence >= 2) {
+        //        break;
+        //    }
+        //    mirHistory.push(opCount);
+        //}
+        //
+        //console.log("After optimizations:");
+        //printMir(mir);
 
         if (this.reporter.errorOccured()) {
             console.error("Errors occurred, stopping compilation.");
             Deno.exit(1);
         }
 
-        const { monoFns, callMap } = new Monomorphizer(ast).monomorphize();
+        const mir = lowerAst(ast);
 
-        const lastPos = await lastPosInTextFile(this.startFilePath);
+        makeMoveCopyExplicit(mir);
+        checkBorrows(mir, this.reporter);
 
-        const lowerer = new Lowerer(monoFns, callMap, lastPos);
-        const { program, fnNames } = lowerer.lower();
-        //lowerer.printProgram();
+        printMir(mir);
 
-        return { program, fnNames };
+        //const { monoFns, callMap } = new Monomorphizer(ast).monomorphize();
+        //
+        //const lastPos = await lastPosInTextFile(this.startFilePath);
+        //
+        //const lowerer = new Lowerer(monoFns, callMap, lastPos);
+        //const { program, fnNames } = lowerer.lower();
+        ////lowerer.printProgram();
+        //
+        //return { program, fnNames };
+        return { program: [], fnNames: {} };
     }
 }
 
diff --git a/compiler/desugar/array_literal.ts b/compiler/desugar/array_literal.ts
index 70cd488..c8bee61 100644
--- a/compiler/desugar/array_literal.ts
+++ b/compiler/desugar/array_literal.ts
@@ -51,6 +51,7 @@ export class ArrayLiteralDesugarer implements AstVisitor {
                     type: "let",
                     param: this.astCreator.param({
                         ident: "::value",
+                        mut: true,
                         pos: npos,
                     }),
                     value: Expr({
diff --git a/compiler/desugar/special_loop.ts b/compiler/desugar/special_loop.ts
index f32a776..3ef127f 100644
--- a/compiler/desugar/special_loop.ts
+++ b/compiler/desugar/special_loop.ts
@@ -72,6 +72,7 @@ export class SpecialLoopDesugarer implements AstVisitor {
                     type: "let",
                     param: this.astCreator.param({
                         ident: "::values",
+                        mut: true,
                         pos: npos,
                     }),
                     value: expr.kind.value,
@@ -80,6 +81,7 @@ export class SpecialLoopDesugarer implements AstVisitor {
                     type: "let",
                     param: this.astCreator.param({
                         ident: "::length",
+                        mut: false,
                         pos: npos,
                     }),
                     value: Expr({
@@ -104,6 +106,7 @@ export class SpecialLoopDesugarer implements AstVisitor {
                     type: "let",
                     param: this.astCreator.param({
                         ident: "::index",
+                        mut: true,
                         pos: npos,
                     }),
                     value: Expr({ type: "int", value: 0 }),
diff --git a/compiler/desugar/struct_literal.ts b/compiler/desugar/struct_literal.ts
index cec22d5..e7a24bf 100644
--- a/compiler/desugar/struct_literal.ts
+++ b/compiler/desugar/struct_literal.ts
@@ -54,6 +54,7 @@ export class StructLiteralDesugarer implements AstVisitor {
                     type: "let",
                     param: this.astCreator.param({
                         ident: "::value",
+                        mut: true,
                         pos: npos,
                     }),
                     value: Expr({
diff --git a/compiler/info.ts b/compiler/info.ts
index bc6d7ff..df1e6d1 100644
--- a/compiler/info.ts
+++ b/compiler/info.ts
@@ -31,7 +31,7 @@ export class Reporter {
     private printReport({ reporter, type, pos, msg }: Report) {
         console.error(
             `${reporter} ${type}: ${msg}${
-                pos ? `\n  at ${this.filePath}:${pos.line}:${pos.col}` : ""
+                pos ? `\n    at ${this.filePath}:${pos.line}:${pos.col}` : ""
             }`,
         );
     }
diff --git a/compiler/lexer.ts b/compiler/lexer.ts
index a962341..f5dd6fd 100644
--- a/compiler/lexer.ts
+++ b/compiler/lexer.ts
@@ -36,6 +36,7 @@ export class Lexer {
                 "break",
                 "return",
                 "let",
+                "mut",
                 "fn",
                 "loop",
                 "if",
@@ -128,7 +129,7 @@ export class Lexer {
             this.step();
             return { ...this.token("string", pos), stringValue: value };
         }
-        if (this.test(/[\+\{\};=\-\*\(\)\.,:;\[\]><!0#]/)) {
+        if (this.test(/[\+\{\};=\-\*\(\)\.,:;\[\]><!0#&]/)) {
             const first = this.current();
             this.step();
             if (first === "=" && !this.done() && this.test("=")) {
diff --git a/compiler/middle/borrow_checker.ts b/compiler/middle/borrow_checker.ts
new file mode 100644
index 0000000..8cb536d
--- /dev/null
+++ b/compiler/middle/borrow_checker.ts
@@ -0,0 +1,240 @@
+import { Reporter } from "../info.ts";
+import { Pos } from "../token.ts";
+import { createCfg } from "./cfg.ts";
+import { Cfg } from "./cfg.ts";
+import { Block, BlockId, Fn, Local, LocalId, Mir, RValue } from "./mir.ts";
+
+export function checkBorrows(
+    mir: Mir,
+    reporter: Reporter,
+) {
+    for (const fn of mir.fns) {
+        new BorrowCheckerFnPass(fn, reporter).pass();
+    }
+}
+
+class BorrowCheckerFnPass {
+    private cfg: Cfg;
+
+    public constructor(
+        private fn: Fn,
+        private reporter: Reporter,
+    ) {
+        this.cfg = createCfg(this.fn);
+    }
+
+    public pass() {
+        for (const local of this.fn.locals) {
+            new LocalChecker(local, this.fn, this.cfg, this.reporter).check();
+        }
+    }
+}
+
+class LocalChecker {
+    private visitedBlocks = new Set<BlockId>();
+
+    private assignedTo = false;
+    private moved = false;
+    private borrowed = false;
+    private borrowedMut = false;
+
+    private movedPos?: Pos;
+    private borrowedPos?: Pos;
+
+    public constructor(
+        private local: Local,
+        private fn: Fn,
+        private cfg: Cfg,
+        private reporter: Reporter,
+    ) {}
+
+    public check() {
+        this.checkBlock(this.cfg.entry());
+    }
+
+    private checkBlock(block: Block) {
+        if (this.visitedBlocks.has(block.id)) {
+            return;
+        }
+        this.visitedBlocks.add(block.id);
+        for (const op of block.ops) {
+            const ok = op.kind;
+            switch (ok.type) {
+                case "error":
+                    break;
+                case "assign":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.src);
+                    break;
+                case "ref":
+                case "ptr":
+                    this.markDst(ok.dst);
+                    this.markBorrow(ok.src);
+                    break;
+                case "ref_mut":
+                case "ptr_mut":
+                    this.markDst(ok.dst);
+                    this.markBorrowMut(ok.src);
+                    break;
+                case "deref":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.src);
+                    break;
+                case "assign_deref":
+                    this.markSrc(ok.subject);
+                    this.markSrc(ok.src);
+                    break;
+                case "field":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.subject);
+                    break;
+                case "assign_field":
+                    this.markSrc(ok.subject);
+                    this.markSrc(ok.src);
+                    break;
+                case "index":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.subject);
+                    this.markSrc(ok.index);
+                    break;
+                case "assign_index":
+                    this.markSrc(ok.subject);
+                    this.markSrc(ok.index);
+                    this.markSrc(ok.src);
+                    break;
+                case "call_val":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.subject);
+                    for (const arg of ok.args) {
+                        this.markSrc(arg);
+                    }
+                    break;
+                case "binary":
+                    this.markDst(ok.dst);
+                    this.markSrc(ok.left);
+                    this.markSrc(ok.right);
+                    break;
+            }
+        }
+        const tk = block.ter.kind;
+        switch (tk.type) {
+            case "error":
+                break;
+            case "return":
+                break;
+            case "jump":
+                break;
+            case "if":
+                this.markSrc(tk.cond);
+                break;
+        }
+        for (const child of this.cfg.children(block)) {
+            this.checkBlock(child);
+        }
+    }
+
+    private markDst(localId: LocalId) {
+        if (localId !== this.local.id) {
+            return;
+        }
+        if (!this.assignedTo) {
+            this.assignedTo = true;
+            return;
+        }
+        if (!this.local.mut) {
+            this.reportReassignToNonMut();
+            return;
+        }
+    }
+
+    private markBorrow(localId: LocalId) {
+        if (localId !== this.local.id) {
+            return;
+        }
+
+        if (!this.assignedTo) {
+            this.assignedTo = true;
+            return;
+        }
+    }
+
+    private markBorrowMut(localId: LocalId) {
+        if (localId !== this.local.id) {
+            return;
+        }
+
+        if (!this.assignedTo) {
+            this.assignedTo = true;
+            return;
+        }
+    }
+
+    private markSrc(src: RValue) {
+        if (src.type === "local") {
+            throw new Error("should be 'copy' or 'move'");
+        }
+        if (
+            (src.type !== "copy" && src.type !== "move") ||
+            src.id !== this.local.id
+        ) {
+            return;
+        }
+        if (src.type === "move") {
+            if (this.moved) {
+                this.reportUseMoved();
+                return;
+            }
+            if (this.borrowed) {
+                this.reportUseBorrowed();
+                return;
+            }
+            this.moved = true;
+        }
+    }
+
+    private reportReassignToNonMut() {
+        const ident = this.local.sym!.ident;
+        this.reporter.reportError({
+            reporter: "borrow checker",
+            msg: `cannot re-assign to '${ident}' as it was not declared mutable`,
+            pos: this.local.sym!.pos!,
+        });
+        this.reporter.addNote({
+            reporter: "borrow checker",
+            msg: `declared here`,
+            pos: this.local.sym!.pos!,
+        });
+    }
+
+    private reportUseMoved() {
+        const ident = this.local.sym!.ident;
+        this.reporter.reportError({
+            reporter: "borrow checker",
+            msg: `cannot use '${ident}' as it has been moved`,
+            pos: this.local.sym!.pos!,
+        });
+        if (this.movedPos) {
+            this.reporter.addNote({
+                reporter: "borrow checker",
+                msg: `moved here`,
+                pos: this.movedPos,
+            });
+        }
+    }
+
+    private reportUseBorrowed() {
+        const ident = this.local.sym!.ident;
+        this.reporter.reportError({
+            reporter: "borrow checker",
+            msg: `cannot use '${ident}' as it has been borrowed`,
+            pos: this.local.sym!.pos!,
+        });
+        if (this.borrowedPos) {
+            this.reporter.addNote({
+                reporter: "borrow checker",
+                msg: `borrowed here`,
+                pos: this.movedPos,
+            });
+        }
+    }
+}
diff --git a/compiler/middle/cfg.ts b/compiler/middle/cfg.ts
index 377b3bc..3f72dfc 100644
--- a/compiler/middle/cfg.ts
+++ b/compiler/middle/cfg.ts
@@ -1,4 +1,4 @@
-import { Block, BlockId, Fn, Mir } from "./mir.ts";
+import { Block, BlockId, Fn } from "./mir.ts";
 
 export function createCfg(fn: Fn): Cfg {
     return new CfgBuilder(fn).build();
@@ -7,10 +7,14 @@ export function createCfg(fn: Fn): Cfg {
 export class Cfg {
     public constructor(
         private graph: Map<BlockId, CfgNode>,
-        private entry: BlockId,
+        private entry_: BlockId,
         private exit: BlockId,
     ) {}
 
+    public entry(): Block {
+        return this.graph.get(this.entry_)!.block;
+    }
+
     public parents(block: Block): Block[] {
         return this.graph
             .get(block.id)!.parents
diff --git a/compiler/middle/elim_transient_locals.ts b/compiler/middle/elim_transient_locals.ts
deleted file mode 100644
index d62c3da..0000000
--- a/compiler/middle/elim_transient_locals.ts
+++ /dev/null
@@ -1,111 +0,0 @@
-import { FnStmtKind } from "../ast.ts";
-import {
-    Block,
-    Fn,
-    Local,
-    LocalId,
-    Mir,
-    replaceBlockSrcs,
-    RValue,
-} from "./mir.ts";
-
-export function eliminateTransientLocals(mir: Mir) {
-    for (const fn of mir.fns) {
-        const otherLocals = fn.locals
-            .slice(1 + (fn.stmt.kind as FnStmtKind).params.length)
-            .map((local) => local.id);
-
-        for (const block of fn.blocks) {
-            new EliminateTransientLocalsBlockPass(block, otherLocals)
-                .pass();
-        }
-    }
-}
-
-type Candidate = {
-    dst: LocalId;
-    src: LocalId;
-};
-
-class EliminateTransientLocalsBlockPass {
-    private candidates: Candidate[] = [];
-
-    public constructor(
-        private block: Block,
-        private readonly locals: LocalId[],
-    ) {
-    }
-
-    public pass() {
-        this.findCandidatesInBlock(this.block);
-
-        this.candidates = this.candidates
-            .filter((cand) => this.locals.includes(cand.dst));
-
-        this.eliminateCandidatesInBlock(this.block);
-    }
-
-    private eliminateCandidatesInBlock(block: Block) {
-        replaceBlockSrcs(block, (src) => this.replaceMaybe(src));
-    }
-
-    private replaceMaybe(src: RValue): RValue {
-        if (src.type !== "local") {
-            return src;
-        }
-        const candidate = this.candidates
-            .find((cand) => cand.dst === src.id)?.src;
-        return candidate !== undefined ? { type: "local", id: candidate } : src;
-    }
-
-    private findCandidatesInBlock(block: Block) {
-        for (const op of block.ops) {
-            const ok = op.kind;
-            switch (ok.type) {
-                case "error":
-                    break;
-                case "assign":
-                    this.markDst(ok.dst, ok.src);
-                    break;
-                case "assign_error":
-                case "assign_null":
-                case "assign_bool":
-                case "assign_int":
-                case "assign_string":
-                case "assign_fn":
-                case "field":
-                case "assign_field":
-                case "index":
-                case "assign_index":
-                case "call_val":
-                case "binary":
-                    break;
-                default:
-                    throw new Error();
-            }
-        }
-        const tk = block.ter.kind;
-        switch (tk.type) {
-            case "error":
-                break;
-            case "return":
-                break;
-            case "jump":
-                break;
-            case "if":
-                break;
-        }
-    }
-
-    private markDst(dst: LocalId, src: RValue) {
-        if (src.type !== "local") {
-            return;
-        }
-
-        this.candidates = this.candidates
-            .filter((cand) => cand.dst !== dst);
-        this.candidates = this.candidates
-            .filter((cand) => cand.src !== dst);
-        this.candidates.push({ dst, src: src.id });
-    }
-}
diff --git a/compiler/middle/elim_transient_vals.ts b/compiler/middle/elim_transient_vals.ts
deleted file mode 100644
index 30c9eeb..0000000
--- a/compiler/middle/elim_transient_vals.ts
+++ /dev/null
@@ -1,99 +0,0 @@
-import { Mir, Op, RValue, visitBlockSrcs } from "./mir.ts";
-
-export function eliminateTransientVals(mir: Mir) {
-    for (const fn of mir.fns) {
-        for (const block of fn.blocks) {
-            const cands: { src: RValue; consumer: Op; definition: Op }[] = [];
-
-            visitBlockSrcs(block, (src, op, i) => {
-                if (src.type !== "local") {
-                    return;
-                }
-                const found = block.ops.find((op, fi) =>
-                    op.kind.type === "assign" &&
-                    op.kind.dst === src.id &&
-                    fi < i!
-                );
-                if (!found) {
-                    return;
-                }
-                cands.push({ src, consumer: op!, definition: found! });
-            });
-
-            //console.log(cands);
-
-            for (const { src: oldsrc, consumer, definition } of cands) {
-                if (oldsrc.type !== "local") {
-                    throw new Error();
-                }
-                if (definition.kind.type !== "assign") {
-                    throw new Error();
-                }
-                const src = definition.kind.src;
-
-                const k = consumer.kind;
-                switch (k.type) {
-                    case "error":
-                        break;
-                    case "assign":
-                        k.src = src;
-                        break;
-                    case "field":
-                        if (same(k.subject, oldsrc)) {
-                            k.subject = src;
-                        }
-                        break;
-                    case "assign_field":
-                        if (same(k.subject, oldsrc)) {
-                            k.subject = src;
-                        }
-                        if (same(k.src, oldsrc)) {
-                            k.src = src;
-                        }
-                        break;
-                    case "index":
-                        if (same(k.subject, oldsrc)) {
-                            k.subject = src;
-                        }
-                        if (same(k.index, oldsrc)) {
-                            k.index = src;
-                        }
-                        break;
-                    case "assign_index":
-                        if (same(k.subject, oldsrc)) {
-                            k.subject = src;
-                        }
-                        if (same(k.index, oldsrc)) {
-                            k.index = src;
-                        }
-                        if (same(k.src, oldsrc)) {
-                            k.src = src;
-                        }
-                        break;
-                    case "call_val":
-                        if (same(k.subject, oldsrc)) {
-                            k.subject = src;
-                        }
-                        for (let i = 0; i < k.args.length; ++i) {
-                            if (same(k.args[i], oldsrc)) {
-                                k.args[i] = src;
-                            }
-                        }
-                        break;
-                    case "binary":
-                        if (same(k.left, oldsrc)) {
-                            k.left = src;
-                        }
-                        if (same(k.right, oldsrc)) {
-                            k.right = src;
-                        }
-                        break;
-                }
-            }
-        }
-    }
-}
-
-function same(a: RValue, b: RValue): boolean {
-    return a.type === "local" && a.type === b.type && a.id === b.id;
-}
diff --git a/compiler/middle/explicit_move_copy.ts b/compiler/middle/explicit_move_copy.ts
new file mode 100644
index 0000000..ea9984c
--- /dev/null
+++ b/compiler/middle/explicit_move_copy.ts
@@ -0,0 +1,58 @@
+import { VType } from "../vtype.ts";
+import { Fn, Local, Mir, replaceBlockSrcs, RValue } from "./mir.ts";
+
+export function makeMoveCopyExplicit(mir: Mir) {
+    for (const fn of mir.fns) {
+        for (const local of fn.locals) {
+            new LocalExpliciter(fn, local).pass();
+        }
+    }
+}
+
+class LocalExpliciter {
+    private copyable: boolean;
+
+    public constructor(private fn: Fn, private local: Local) {
+        this.copyable = copyableIsType(local.vtype);
+    }
+
+    public pass() {
+        for (const block of this.fn.blocks) {
+            replaceBlockSrcs(block, (src) => this.explicitSrc(src));
+        }
+    }
+
+    private explicitSrc(src: RValue): RValue {
+        if (src.type !== "local") {
+            return src;
+        }
+        return this.copyable
+            ? { type: "copy", id: src.id }
+            : { type: "move", id: src.id };
+    }
+}
+
+function copyableIsType(vtype: VType): boolean {
+    switch (vtype.type) {
+        case "error":
+        case "unknown":
+            throw new Error();
+        case "null":
+        case "int":
+        case "bool":
+        case "string":
+        case "ref":
+        case "ref_mut":
+        case "ptr":
+        case "ptr_mut":
+            return true;
+        case "array":
+        case "struct":
+        case "fn":
+            return false;
+        case "generic":
+            return false;
+        case "generic_spec":
+            throw new Error();
+    }
+}
diff --git a/compiler/middle/lower_ast.ts b/compiler/middle/lower_ast.ts
index edbe27b..8c1b408 100644
--- a/compiler/middle/lower_ast.ts
+++ b/compiler/middle/lower_ast.ts
@@ -103,7 +103,7 @@ class FnAstLowerer {
                     const val = this.lowerExpr(stmt.kind.expr);
                     this.addOp({ type: "assign", dst, src: local(val) });
                 } else {
-                    this.addOp({ type: "assign_null", dst });
+                    this.addOp({ type: "assign", dst, src: { type: "null" } });
                 }
                 this.setTer({ type: "jump", target: block });
                 this.pushBlock();
@@ -227,6 +227,24 @@ class FnAstLowerer {
                 return this.lowerSymExpr(expr);
             case "group":
                 return this.lowerExpr(expr.kind.expr);
+            case "ref": {
+                const src = this.lowerExpr(expr.kind.subject);
+                const dst = this.locals.alloc(expr.vtype!);
+                this.addOp({ type: "ref", dst, src });
+                return dst;
+            }
+            case "ref_mut": {
+                const src = this.lowerExpr(expr.kind.subject);
+                const dst = this.locals.alloc(expr.vtype!);
+                this.addOp({ type: "ref_mut", dst, src });
+                return dst;
+            }
+            case "deref": {
+                const src = local(this.lowerExpr(expr.kind.subject));
+                const dst = this.locals.alloc(expr.kind.subject.vtype!);
+                this.addOp({ type: "deref", dst, src });
+                return dst;
+            }
             case "array":
                 throw new Error("incomplete desugar");
             case "struct":
@@ -274,7 +292,7 @@ class FnAstLowerer {
                     throw new Error();
                 }
                 const dst = this.locals.alloc(sym.stmt.kind.vtype!);
-                this.addOp({ type: "assign_fn", dst, stmt });
+                this.addOp({ type: "assign", dst, src: { type: "fn", stmt } });
                 return dst;
             }
             case "fn_param": {
@@ -320,7 +338,7 @@ class FnAstLowerer {
         const dstVType = ((): VType => {
             const outer = expr.kind.subject.vtype!;
             if (outer.type === "array") {
-                return outer.inner;
+                return outer.subject;
             }
             if (outer.type === "string") {
                 return { type: "int" };
@@ -442,7 +460,7 @@ class FnAstLowerer {
             return this.lowerExpr(expr.kind.expr);
         } else {
             const local = this.locals.alloc({ type: "null" });
-            this.addOp({ type: "assign_null", dst: local });
+            this.addOp({ type: "assign", dst: local, src: { type: "null" } });
             return local;
         }
     }
diff --git a/compiler/middle/mir.ts b/compiler/middle/mir.ts
index d2f674a..128e384 100644
--- a/compiler/middle/mir.ts
+++ b/compiler/middle/mir.ts
@@ -41,6 +41,13 @@ type R = RValue;
 export type OpKind =
     | { type: "error" }
     | { type: "assign"; dst: L; src: R }
+    | { type: "ref"; dst: L; src: L }
+    | { type: "ref_mut"; dst: L; src: L }
+    | { type: "ptr"; dst: L; src: L }
+    | { type: "ptr_mut"; dst: L; src: L }
+    | { type: "drop"; src: L }
+    | { type: "deref"; dst: L; src: R }
+    | { type: "assign_deref"; subject: R; src: R }
     | { type: "field"; dst: L; subject: R; ident: string }
     | { type: "assign_field"; subject: R; ident: string; src: R }
     | { type: "index"; dst: L; subject: R; index: R }
@@ -61,6 +68,8 @@ export type TerKind =
 export type RValue =
     | { type: "error" }
     | { type: "local"; id: BlockId }
+    | { type: "copy"; id: BlockId }
+    | { type: "move"; id: BlockId }
     | { type: "null" }
     | { type: "bool"; val: boolean }
     | { type: "int"; val: number }
@@ -77,12 +86,18 @@ export function visitBlockDsts(
             case "error":
                 break;
             case "assign":
+            case "ref":
+            case "ref_mut":
+            case "ptr":
+            case "ptr_mut":
+            case "deref":
             case "field":
             case "index":
             case "call_val":
             case "binary":
                 visit(ok.dst, i);
                 break;
+            case "assign_deref":
             case "assign_field":
             case "assign_index":
                 break;
@@ -104,6 +119,19 @@ export function replaceBlockSrcs(
             case "assign":
                 ok.src = replace(ok.src);
                 break;
+            case "ref":
+            case "ref_mut":
+            case "ptr":
+            case "ptr_mut":
+            case "drop":
+                break;
+            case "deref":
+                ok.src = replace(ok.src);
+                break;
+            case "assign_deref":
+                ok.subject = replace(ok.subject);
+                ok.src = replace(ok.src);
+                break;
             case "field":
                 ok.subject = replace(ok.subject);
                 break;
@@ -158,6 +186,19 @@ export function visitBlockSrcs(
             case "assign":
                 visitor(ok.src, op, i);
                 break;
+            case "ref":
+            case "ref_mut":
+            case "ptr":
+            case "ptr_mut":
+            case "drop":
+                break;
+            case "deref":
+                visitor(ok.src, op, i);
+                break;
+            case "assign_deref":
+                visitor(ok.src, op, i);
+                visitor(ok.subject, op, i);
+                break;
             case "field":
                 visitor(ok.subject, op, i);
                 break;
@@ -254,6 +295,27 @@ export function printMir(mir: Mir) {
                     case "assign":
                         l(`_${k.dst} = ${r(k.src)};`);
                         break;
+                    case "ref":
+                        l(`_${k.dst} = &_${k.src};`);
+                        break;
+                    case "ref_mut":
+                        l(`_${k.dst} = &mut _${k.src};`);
+                        break;
+                    case "ptr":
+                        l(`_${k.dst} = *_${k.src};`);
+                        break;
+                    case "ptr_mut":
+                        l(`_${k.dst} = *mut _${k.src};`);
+                        break;
+                    case "drop":
+                        l(`drop _${k.src};`);
+                        break;
+                    case "deref":
+                        l(`_${k.dst} = *${r(k.src)};`);
+                        break;
+                    case "assign_deref":
+                        l(`*${r(k.subject)} = ${r(k.src)};`);
+                        break;
                     case "field":
                         l(`_${k.dst} = ${r(k.subject)}.${k.ident};`);
                         break;
@@ -277,6 +339,8 @@ export function printMir(mir: Mir) {
                         };`);
                         break;
                     }
+                    default:
+                        throw new Error();
                 }
             }
             const tk = block.ter.kind;
@@ -295,6 +359,8 @@ export function printMir(mir: Mir) {
                         r(tk.cond)
                     }, true: bb${tk.truthy}, false: bb${tk.falsy};`);
                     break;
+                default:
+                    throw new Error();
             }
             console.log("    }");
         }
@@ -308,6 +374,10 @@ export function rvalueToString(rvalue: RValue): string {
             return `<error>`;
         case "local":
             return `_${rvalue.id}`;
+        case "copy":
+            return `copy _${rvalue.id}`;
+        case "move":
+            return `move _${rvalue.id}`;
         case "null":
             return "null";
         case "bool":
diff --git a/compiler/mono.ts b/compiler/mono.ts
index 45a1cb3..d7abd63 100644
--- a/compiler/mono.ts
+++ b/compiler/mono.ts
@@ -163,8 +163,16 @@ function vtypeNameGenPart(vtype: VType): string {
         case "null":
         case "unknown":
             return vtype.type;
+        case "ref":
+            return `&${vtypeNameGenPart(vtype.subject)}`;
+        case "ref_mut":
+            return `&mut ${vtypeNameGenPart(vtype.subject)}`;
+        case "ptr":
+            return `*${vtypeNameGenPart(vtype.subject)}`;
+        case "ptr_mut":
+            return `*mut ${vtypeNameGenPart(vtype.subject)}`;
         case "array":
-            return `[${vtypeNameGenPart(vtype.inner)}]`;
+            return `[${vtypeNameGenPart(vtype.subject)}]`;
         case "struct": {
             const fields = vtype.fields
                 .map((field) =>
diff --git a/compiler/parser.ts b/compiler/parser.ts
index a423b51..4c02eb4 100644
--- a/compiler/parser.ts
+++ b/compiler/parser.ts
@@ -388,7 +388,12 @@ export class Parser {
 
     private parseParam(index?: number): Res<Param> {
         const pos = this.pos();
-        if (this.test("ident")) {
+        if (this.test("ident") || this.test("mut")) {
+            let mut = false;
+            if (this.test("mut")) {
+                mut = true;
+                this.step();
+            }
             const ident = this.current().identValue!;
             this.step();
             if (this.test(":")) {
@@ -396,12 +401,18 @@ export class Parser {
                 const etype = this.parseEType();
                 return {
                     ok: true,
-                    value: this.astCreator.param({ index, ident, etype, pos }),
+                    value: this.astCreator.param({
+                        index,
+                        ident,
+                        mut,
+                        etype,
+                        pos,
+                    }),
                 };
             }
             return {
                 ok: true,
-                value: this.astCreator.param({ index, ident, pos }),
+                value: this.astCreator.param({ index, ident, mut, pos }),
             };
         }
         this.report("expected param");
@@ -779,6 +790,21 @@ export class Parser {
             const subject = this.parsePrefix();
             return this.expr({ type: "unary", unaryType, subject }, pos);
         }
+        if (this.test("&")) {
+            this.step();
+            let type: "ref" | "ref_mut" = "ref";
+            if (this.test("mut")) {
+                this.step();
+                type = "ref_mut";
+            }
+            const subject = this.parsePrefix();
+            return this.expr({ type, subject }, pos);
+        }
+        if (this.test("*")) {
+            this.step();
+            const subject = this.parsePrefix();
+            return this.expr({ type: "deref", subject }, pos);
+        }
         return this.parsePostfix();
     }
 
@@ -955,13 +981,13 @@ export class Parser {
         }
         if (this.test("[")) {
             this.step();
-            const inner = this.parseEType();
+            const subject = this.parseEType();
             if (!this.test("]")) {
                 this.report("expected ']'", pos);
                 return this.etype({ type: "error" }, pos);
             }
             this.step();
-            return this.etype({ type: "array", inner }, pos);
+            return this.etype({ type: "array", subject }, pos);
         }
         if (this.test("struct")) {
             this.step();
@@ -972,6 +998,26 @@ export class Parser {
             const fields = this.parseETypeStructFields();
             return this.etype({ type: "struct", fields }, pos);
         }
+        if (this.test("&")) {
+            this.step();
+            let type: "ref" | "ref_mut" = "ref";
+            if (this.test("mut")) {
+                this.step();
+                type = "ref_mut";
+            }
+            const subject = this.parseEType();
+            return this.etype({ type, subject }, pos);
+        }
+        if (this.test("*")) {
+            this.step();
+            let type: "ptr" | "ptr_mut" = "ptr";
+            if (this.test("mut")) {
+                this.step();
+                type = "ptr_mut";
+            }
+            const subject = this.parseEType();
+            return this.etype({ type, subject }, pos);
+        }
         this.report("expected type");
         return this.etype({ type: "error" }, pos);
     }
diff --git a/compiler/resolver.ts b/compiler/resolver.ts
index b8afa4c..55723d9 100644
--- a/compiler/resolver.ts
+++ b/compiler/resolver.ts
@@ -107,7 +107,7 @@ export class Resolver implements AstVisitor<[Syms]> {
         return "stop";
     }
 
-    visitTypeAliasStmt(stmt: Stmt, syms: Syms): VisitRes {
+    visitTypeAliasStmt(stmt: Stmt, _syms: Syms): VisitRes {
         if (stmt.kind.type !== "type_alias") {
             throw new Error("expected type_alias statement");
         }
diff --git a/compiler/vtype.ts b/compiler/vtype.ts
index 48a8d8e..24946e8 100644
--- a/compiler/vtype.ts
+++ b/compiler/vtype.ts
@@ -5,7 +5,11 @@ export type VType =
     | { type: "int" }
     | { type: "string" }
     | { type: "bool" }
-    | { type: "array"; inner: VType }
+    | { type: "ref"; subject: VType }
+    | { type: "ref_mut"; subject: VType }
+    | { type: "ptr"; subject: VType }
+    | { type: "ptr_mut"; subject: VType }
+    | { type: "array"; subject: VType }
     | { type: "struct"; fields: VTypeParam[] }
     | {
         type: "fn";
@@ -45,8 +49,20 @@ export function vtypesEqual(
     ) {
         return true;
     }
+    if (a.type === "ref" && b.type === "ref") {
+        return vtypesEqual(a.subject, b.subject, generics);
+    }
+    if (a.type === "ref_mut" && b.type === "ref_mut") {
+        return vtypesEqual(a.subject, b.subject, generics);
+    }
+    if (a.type === "ptr" && b.type === "ptr") {
+        return vtypesEqual(a.subject, b.subject, generics);
+    }
+    if (a.type === "ptr_mut" && b.type === "ptr_mut") {
+        return vtypesEqual(a.subject, b.subject, generics);
+    }
     if (a.type === "array" && b.type === "array") {
-        return vtypesEqual(a.inner, b.inner, generics);
+        return vtypesEqual(a.subject, b.subject, generics);
     }
     if (a.type === "struct" && b.type === "struct") {
         if (a.fields.length !== b.fields.length) {
@@ -117,8 +133,20 @@ export function vtypeToString(vtype: VType): string {
     ) {
         return vtype.type;
     }
+    if (vtype.type === "ref") {
+        return `&${vtypeToString(vtype.subject)}`;
+    }
+    if (vtype.type === "ref_mut") {
+        return `&mut ${vtypeToString(vtype.subject)}`;
+    }
+    if (vtype.type === "ptr") {
+        return `*${vtypeToString(vtype.subject)}`;
+    }
+    if (vtype.type === "ptr_mut") {
+        return `*mut ${vtypeToString(vtype.subject)}`;
+    }
     if (vtype.type === "array") {
-        return `[${vtypeToString(vtype.inner)}]`;
+        return `[${vtypeToString(vtype.subject)}]`;
     }
     if (vtype.type === "struct") {
         const fields = vtype.fields
diff --git a/examples/example_2.slg b/examples/example_2.slg
index 45134ae..1dac50e 100644
--- a/examples/example_2.slg
+++ b/examples/example_2.slg
@@ -4,7 +4,14 @@ fn add(a: int, b: int) -> int {
 
 fn main() -> int {
     let result = 0;
-    let i = 0;
+
+    let a  = 0;
+    let b  = a;
+    let c  = b;
+    let d  = c;
+
+
+    let i = c;
     loop {
         if i >= 10 {
             break;
diff --git a/examples/refs.slg b/examples/refs.slg
new file mode 100644
index 0000000..8616137
--- /dev/null
+++ b/examples/refs.slg
@@ -0,0 +1,7 @@
+//
+
+fn main() {
+    let a = 5;
+    let b: &int = &a;
+}
+