---
id: maps-records
title: Records and Maps
---

import Syntax from '@theme/Syntax';

So far we have seen pretty basic data types. LIGO also offers more
complex built-in constructs, such as *records* and *maps*.

## Records

Records are one way data of different types can be packed into a
single type. A record is made of a set of *fields*, which are made of
a *field name* and a *field type*. Given a value of a record type, the
value bound to a field can be accessed by giving its field name to a
special operator (`.`).

Let us first consider and example of record type declaration.



<Syntax syntax="pascaligo">

```pascaligo group=records1
type user is
  record [
    id       : nat;
    is_admin : bool;
    name     : string
  ]
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=records1
type user = {
  id       : nat;
  is_admin : bool;
  name     : string
}
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=records1
type user = {
  id       : nat,
  is_admin : bool,
  name     : string
};
```

</Syntax>


And here is how a record value is defined:


<Syntax syntax="pascaligo">

```pascaligo group=records1
const alice : user =
  record [
    id       = 1n;
    is_admin = True;
    name     = "Alice"
  ]
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=records1
let alice : user = {
  id       = 1n;
  is_admin = true;
  name     = "Alice"
}
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=records1
let alice : user = {
  id       : 1n,
  is_admin : true,
  name     : "Alice"
};
```

</Syntax>


### Accessing Record Fields

If we want the contents of a given field, we use the (`.`) infix
operator, like so:


<Syntax syntax="pascaligo">

```pascaligo group=records1
const alice_admin : bool = alice.is_admin
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=records1
let alice_admin : bool = alice.is_admin
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=records1
let alice_admin : bool = alice.is_admin;
```

</Syntax>


### Functional Updates

Given a record value, it is a common design pattern to update only a
small number of its fields. Instead of copying the fields that are
unchanged, LIGO offers a way to only update the fields that are
modified.

One way to understand the update of record values is the *functional
update*. The idea is to have an *expression* whose value is the
updated record.

Let us consider defining a function that translates three-dimensional
points on a plane.

<Syntax syntax="pascaligo">

In PascaLIGO, the shape of that expression is
`<record variable> with <record value>`.
The record variable is the record to update and the
record value is the update itself.

```pascaligo group=records2
type point is record [x : int; y : int; z : int]
type vector is record [dx : int; dy : int]

const origin : point = record [x = 0; y = 0; z = 0]

function xy_translate (var p : point; const vec : vector) : point is
  p with record [x = p.x + vec.dx; y = p.y + vec.dy]
```

You can call the function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_update.ligo
translate "(record [x=2;y=3;z=1], record [dx=3;dy=4])"
# Outputs: {z = 1 , y = 7 , x = 5}
```

You have to understand that `p` has not been changed by the functional
update: a namless new version of it has been created and returned by
the blockless function.

</Syntax>
<Syntax syntax="cameligo">

The syntax for the functional updates of record in CameLIGO follows
that of OCaml:

```cameligo group=records2
type point = {x : int; y : int; z : int}
type vector = {dx : int; dy : int}

let origin : point = {x = 0; y = 0; z = 0}

let xy_translate (p, vec : point * vector) : point =
  {p with x = p.x + vec.dx; y = p.y + vec.dy}
```

You can call the function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_update.mligo
xy_translate "({x=2;y=3;z=1}, {dx=3;dy=4})"
# Outputs: {z = 1 , y = 7 , x = 5}
```

> You have to understand that `p` has not been changed by the
> functional update: a nameless new version of it has been created and
> returned.

</Syntax>
<Syntax syntax="reasonligo">

The syntax for the functional updates of record in ReasonLIGO follows
that of ReasonML:

```reasonligo group=records2
type point = {x : int, y : int, z : int};
type vector = {dx : int, dy : int};

let origin : point = {x : 0, y : 0, z : 0};

let xy_translate = ((p, vec) : (point, vector)) : point =>
  {...p, x : p.x + vec.dx, y : p.y + vec.dy};
```

</Syntax>


You can call the function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_update.religo
xy_translate "({x:2,y:3,z:1}, {dx:3,dy:4})"
# Outputs: {z = 1 , y = 7 , x = 5}
```

You have to understand that `p` has not been changed by the functional
update: a nameless new version of it has been created and returned.

#### Nested updates

A unique feature of LIGO is the ability to perform nested updates on records.

For example if you have the following record structure:

<Syntax syntax="pascaligo">

```pascaligo
type color is
| Blue
| Green

type preferences is record [
  color : color;
  other : int;
]

type account is record [
  id : int;
  preferences : preferences;
]
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo
type color =
  Blue
| Green

type preferences = {
  color : color;
  other : int;
}

type account = {
  id: int;
  preferences: preferences;
}
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo
type color =
  Blue
| Green;

type preferences = {
  color : color,
  other : int
}

type account = {
  id : int,
  preferences : preferences
}
```

</Syntax>

You can update the nested record with the following code:

<Syntax syntax="pascaligo">

```pascaligo

function change_color_preference (const account : account; const color : color ) : account is
  block {
      account := account with record [preferences.color = color]
  } with account

```

</Syntax>
<Syntax syntax="cameligo">

```cameligo
let change_color_preference (account : account) (color : color) : account =
  { account with preferences.color = color }
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo
let change_color_preference = (account : account, color : color): account =>
  { ...account, preferences.color: color };
```

</Syntax>

Note that all the records in the path will get updated. In this example that's
`account` and `preferences`.

<Syntax syntax="pascaligo">

### Record Patches

Another way to understand what it means to update a record value is to
make sure that any further reference to the value afterwards will
exhibit the modification. This is called a `patch` and this is only
possible in PascaLIGO, because a patch is an *instruction*, therefore
we can only use it in a block. Similarly to a *functional update*, a
patch takes a record to be updated and a record with a subset of the
fields to update, then applies the latter to the former (hence the
name "patch").

Let us consider defining a function that translates three-dimensional
points on a plane.

```pascaligo group=records3
type point is record [x : int; y : int; z : int]
type vector is record [dx : int; dy : int]

function xy_translate (var p : point; const vec : vector) : point is
  block {
    patch p with record [x = p.x + vec.dx];
    patch p with record [y = p.y + vec.dy]
  } with p
```

You can call the function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_patch.ligo
xy_translate "(record [x=2;y=3;z=1], record [dx=3;dy=4])"
# Outputs: {z = 1 , y = 7 , x = 5}
```

Of course, we can actually translate the point with only one `patch`,
as the previous example was meant to show that, after the first patch,
the value of `p` indeed changed. So, a shorter version would be

```pascaligo group=records4
type point is record [x : int; y : int; z : int]
type vector is record [dx : int; dy : int]

function xy_translate (var p : point; const vec : vector) : point is
  block {
    patch p with record [x = p.x + vec.dx; y = p.y + vec.dy]
  } with p
```

You can call the new function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_patch2.ligo
xy_translate "(record [x=2;y=3;z=1], record [dx=3;dy=4])"
# Outputs: {z = 1 , y = 7 , x = 5}
```

Record patches can actually be simulated with functional updates. All
we have to do is *declare a new record value with the same name as the
one we want to update* and use a functional update, like so:

```pascaligo group=records5
type point is record [x : int; y : int; z : int]
type vector is record [dx : int; dy : int]

function xy_translate (var p : point; const vec : vector) : point is
  block {
    const p : point = p with record [x = p.x + vec.dx; y = p.y + vec.dy]
  } with p
```

You can call the new function `xy_translate` defined above by running the
following command of the shell:
```shell
ligo run-function
gitlab-pages/docs/language-basics/src/maps-records/record_simu.ligo
xy_translate "(record [x=2;y=3;z=1], record [dx=3;dy=4])"
# Outputs: {z = 1 , y = 7 , x = 5}
```

The hiding of a variable by another (here `p`) is called `shadowing`.

</Syntax>

## Maps

*Maps* are a data structure which associate values of the same type to
values of the same type. The former are called *key* and the latter
*values*. Together they make up a *binding*. An additional requirement
is that the type of the keys must be *comparable*, in the Michelson
sense.

### Declaring a Map

Here is how a custom map from addresses to a pair of integers is
defined.



<Syntax syntax="pascaligo">

```pascaligo group=maps
type move is int * int
type register is map (address, move)
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
type move = int * int
type register = (address, move) map
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
type move = (int, int);
type register = map (address, move);
```

</Syntax>


### Creating an Empty Map

Here is how to create an empty map.



<Syntax syntax="pascaligo">

```pascaligo group=maps
const empty : register = map []
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let empty : register = Map.empty
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let empty : register = Map.empty
```

</Syntax>


### Creating a Non-empty Map

And here is how to create a non-empty map value:


<Syntax syntax="pascaligo">

```pascaligo group=maps
const moves : register =
  map [
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address) -> (1,2);
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) -> (0,3)]
```

Notice the `->` between the key and its value and `;` to separate
individual map entries. The annotated value `("<string value>" :
address)` means that we cast a string into an address. Also, `map` is
a keyword.

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let moves : register =
  Map.literal [
    (("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address), (1,2));
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address), (0,3))]
```

The `Map.literal` predefined function builds a map from a list of
key-value pair tuples, `(<key>, <value>)`.  Note also the `;` to
separate individual map entries.  `("<string value>": address)` means
that we type-cast a string into an address. -->

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let moves : register =
  Map.literal ([
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address, (1,2)),
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address, (0,3))]);
```

The `Map.literal` predefined function builds a map from a list of
key-value pair tuples, `(<key>, <value>)`.  Note also the `;` to
separate individual map entries.  `("<string value>": address)` means
that we type-cast a string into an address. -->

</Syntax>


### Accessing Map Bindings


<Syntax syntax="pascaligo">

In PascaLIGO, we can use the postfix `[]` operator to read the `move`
value associated to a given key (`address` here) in the register. Here
is an example:

```pascaligo group=maps
const my_balance : option (move) =
  moves [("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address)]
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let my_balance : move option =
  Map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) moves
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let my_balance : option (move) =
  Map.find_opt (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address), moves);
```

</Syntax>


Notice how the value we read is an optional value: this is to force
the reader to account for a missing key in the map. This requires
*pattern matching*.



<Syntax syntax="pascaligo">

```pascaligo group=maps
function force_access (const key : address; const moves : register) : move is
  case moves[key] of
    Some (move) -> move
  | None -> (failwith ("No move.") : move)
  end
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let force_access (key, moves : address * register) : move =
  match Map.find_opt key moves with
    Some move -> move
  | None -> (failwith "No move." : move)
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let force_access = ((key, moves) : (address, register)) : move => {
  switch (Map.find_opt (key, moves)) {
  | Some (move) => move
  | None => failwith ("No move.") : move
  }
};
```

</Syntax>



### Updating a Map

Given a map, we may want to add a new binding, remove one, or modify
one by changing the value associated to an already existing key. All
those operations are called *updates*.



<Syntax syntax="pascaligo">

The values of a PascaLIGO map can be updated using the usual
assignment syntax `<map variable>[<key>] := <new value>`. Let us
consider an example.

```pascaligo group=maps
function assign (var m : register) : register is
  block {
    m [("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)] := (4,9)
  } with m
```

If multiple bindings need to be updated, PascaLIGO offers a *patch
instruction* for maps, similar to that for records.

```pascaligo group=maps
function assignments (var m : register) : register is
  block {
    patch m with map [
      ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) -> (4,9);
      ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address) -> (1,2)
    ]
  } with m
```

See further for the removal of bindings.

</Syntax>
<Syntax syntax="cameligo">

We can update a binding in a map in CameLIGO by means of the
`Map.update` built-in function:

```cameligo group=maps
let assign (m : register) : register =
  Map.update
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) (Some (4,9)) m
```

Notice the optional value `Some (4,9)` instead of `(4,9)`. If we had
use `None` instead, that would have meant that the binding is removed.

As a particular case, we can only add a key and its associated value.

```cameligo group=maps
let add (m : register) : register =
  Map.add
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) (4,9) m
```

</Syntax>
<Syntax syntax="reasonligo">

We can update a binding in a map in ReasonLIGO by means of the
`Map.update` built-in function:

```reasonligo group=maps
let assign = (m : register) : register =>
  Map.update
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address), Some ((4,9)), m);
```

Notice the optional value `Some (4,9)` instead of `(4,9)`. If we had
use `None` instead, that would have meant that the binding is removed.

As a particular case, we can only add a key and its associated value.

```reasonligo group=maps
let add = (m : register) : register =>
  Map.add
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address), (4,9), m);
```

</Syntax>


To remove a binding from a map, we need its key.



<Syntax syntax="pascaligo">

In PascaLIGO, there is a special instruction to remove a binding from
a map.
```pascaligo group=maps
function delete (const key : address; var moves : register) : register is
  block {
    remove key from map moves
  } with moves
```

</Syntax>
<Syntax syntax="cameligo">

In CameLIGO, we use the predefined function `Map.remove` as follows:

```cameligo group=maps
let delete (key, moves : address * register) : register =
  Map.remove key moves
```

</Syntax>
<Syntax syntax="reasonligo">

In ReasonLIGO, we use the predefined function `Map.remove` as follows:

```reasonligo group=maps
let delete = ((key, moves) : (address, register)) : register =>
  Map.remove (key, moves);
```

</Syntax>



### Functional Iteration over Maps

A *functional iterator* is a function that traverses a data structure
and calls in turn a given function over the elements of that structure
to compute some value. Another approach is possible in PascaLIGO:
*loops* (see the relevant section).

There are three kinds of functional iterations over LIGO maps: the
*iterated operation*, the *map operation* (not to be confused with the
*map data structure*) and the *fold operation*.

#### Iterated Operation over Maps

The first, the *iterated operation*, is an iteration over the map with
no return value: its only use is to produce side-effects. This can be
useful if for example you would like to check that each value inside
of a map is within a certain range, and fail with an error otherwise.

The predefined functional iterator implementing the iterated operation
over maps is called `Map.iter`. In the following example, the register
of moves is iterated to check that the start of each move is above
`3`.



<Syntax syntax="pascaligo">

```pascaligo group=maps
function iter_op (const m : register) : unit is
  block {
    function iterated (const i : address; const j : move) : unit is
      if j.1 > 3 then Unit else (failwith ("Below range.") : unit)
  } with Map.iter (iterated, m)
```

> Note that `map_iter` is *deprecated*.

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let iter_op (m : register) : unit =
  let predicate = fun (i,j : address * move) -> assert (j.0 > 3)
  in Map.iter predicate m
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let iter_op = (m : register) : unit => {
  let predicate = ((i,j) : (address, move)) => assert (j[0] > 3);
  Map.iter (predicate, m);
};
```

</Syntax>


#### Map Operations over Maps

We may want to change all the bindings of a map by applying to them a
function. This is called a *map operation*, not to be confused with
the map data structure. The predefined functional iterator
implementing the map operation over maps is called `Map.map`. In the
following example, we add `1` to the ordinate of the moves in the
register.



<Syntax syntax="pascaligo">

```pascaligo group=maps
function map_op (const m : register) : register is
  block {
    function increment (const i : address; const j : move) : move is
      (j.0, j.1 + 1)
  } with Map.map (increment, m)
```

> Note that `map_map` is *deprecated*.

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let map_op (m : register) : register =
  let increment = fun (i,j : address * move) -> j.0, j.1 + 1
  in Map.map increment m
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let map_op = (m : register) : register => {
  let increment = ((i,j): (address, move)) => (j[0], j[1] + 1);
  Map.map (increment, m);
};
```

</Syntax>


#### Folded Operations over Maps

A *folded operation* is the most general of iterations. The folded
function takes two arguments: an *accumulator* and the structure
*element* at hand, with which it then produces a new accumulator. This
enables having a partial result that becomes complete when the
traversal of the data structure is over.

The predefined functional iterator implementing the folded operation
over maps is called `Map.fold` and is used as follows.



<Syntax syntax="pascaligo">

```pascaligo group=maps
function fold_op (const m : register) : int is
  block {
    function folded (const i : int; const j : address * move) : int is
      i + j.1.1
  } with Map.fold (folded, m, 5)
```

> Note that `map_fold` is *deprecated*.

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=maps
let fold_op (m : register) : int =
  let folded = fun (i,j : int * (address * move)) -> i + j.1.1
  in Map.fold folded m 5
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=maps
let fold_op = (m : register) : int => {
  let folded = ((i,j): (int, (address, move))) => i + j[1][1];
  Map.fold (folded, m, 5);
};
```

</Syntax>


## Big Maps

Ordinary maps are fine for contracts with a finite lifespan or a
bounded number of users. For many contracts however, the intention is
to have a map holding *many* entries, potentially millions of
them. The cost of loading those entries into the environment each time
a user executes the contract would eventually become too expensive
were it not for *big maps*. Big maps are a data structure offered by
Michelson which handles the scaling concerns for us. In LIGO, the
interface for big maps is analogous to the one used for ordinary maps.

### Declaring a Map

Here is how we define a big map:


<Syntax syntax="pascaligo">

```pascaligo group=big_maps
type move is int * int
type register is big_map (address, move)
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=big_maps
type move = int * int
type register = (address, move) big_map
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=big_maps
type move = (int, int);
type register = big_map (address, move);
```

</Syntax>


### Creating an Empty Big Map

Here is how to create an empty big map.




<Syntax syntax="pascaligo">

```pascaligo group=big_maps
const empty : register = big_map []
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=big_maps
let empty : register = Big_map.empty
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=big_maps
let empty : register = Big_map.empty
```

</Syntax>


### Creating a Non-empty Map

And here is how to create a non-empty map value:


<Syntax syntax="pascaligo">

```pascaligo group=big_maps
const moves : register =
  big_map [
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address) -> (1,2);
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) -> (0,3)]
```

Notice the right arrow `->` between the key and its value and the
semicolon separating individual map entries. The value annotation
`("<string value>" : address)` means that we cast a string into an
address. -->

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=big_maps
let moves : register =
  Big_map.literal [
    (("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address), (1,2));
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address), (0,3))]
```

The predefind function `Big_map.literal` constructs a big map from a
list of key-value pairs `(<key>, <value>)`. Note also the semicolon
separating individual map entries.  The annotated value `("<string>
value>" : address)` means that we cast a string into an address.

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=big_maps
let moves : register =
  Big_map.literal ([
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address, (1,2)),
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address, (0,3))]);
```

The predefind function `Big_map.literal` constructs a big map from a
list of key-value pairs `(<key>, <value>)`. Note also the semicolon
separating individual map entries.  The annotated value `("<string>
value>" : address)` means that we cast a string into an address.

</Syntax>


### Accessing Values

If we want to access a move from our `register` above, we can use the
postfix `[]` operator to read the associated `move` value. However,
the value we read is an optional value (in our case, of type `option
(move)`), to account for a missing key. Here is an example:



<Syntax syntax="pascaligo">

```pascaligo group=big_maps
const my_balance : option (move) =
  moves [("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address)]
```

</Syntax>
<Syntax syntax="cameligo">

```cameligo group=big_maps
let my_balance : move option =
  Big_map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) moves
```

</Syntax>
<Syntax syntax="reasonligo">

```reasonligo group=big_maps
let my_balance : option (move) =
  Big_map.find_opt ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address, moves);
```

</Syntax>


### Updating Big Maps



<Syntax syntax="pascaligo">

The values of a PascaLIGO big map can be updated using the
assignment syntax for ordinary maps

```pascaligo group=big_maps
function assign (var m : register) : register is
  block {
    m [("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address)] := (4,9)
  } with m
```

If multiple bindings need to be updated, PascaLIGO offers a *patch
instruction* for maps, similar to that for records.

```pascaligo group=big_maps
function assignments (var m : register) : register is
  block {
    patch m with map [
      ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) -> (4,9);
      ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx" : address) -> (1,2)
    ]
  } with m
```

</Syntax>
<Syntax syntax="cameligo">

We can update a big map in CameLIGO using the `Big_map.update`
built-in:

```cameligo group=big_maps
let updated_map : register =
  Big_map.update
    ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN" : address) (Some (4,9)) moves
```

</Syntax>
<Syntax syntax="reasonligo">

We can update a big map in ReasonLIGO using the `Big_map.update`
built-in:

```reasonligo group=big_maps
let updated_map : register =
  Big_map.update
    (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), Some ((4,9)), moves);
```

</Syntax>


### Removing Bindings

Removing a binding in a map is done differently according to the LIGO
syntax.



<Syntax syntax="pascaligo">

PascaLIGO features a special syntactic construct to remove bindings
from maps, of the form `remove <key> from map <map>`. For example,

```pascaligo group=big_maps
function rem (var m : register) : register is
  block {
    remove ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) from map moves
  } with m

const updated_map : register = rem (moves)
```

</Syntax>
<Syntax syntax="cameligo">

In CameLIGO, the predefined function which removes a binding in a map
is called `Map.remove` and is used as follows:

```cameligo group=big_maps
let updated_map : register =
  Map.remove ("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address) moves
```

</Syntax>
<Syntax syntax="reasonligo">

In ReasonLIGO, the predefined function which removes a binding in a map
is called `Map.remove` and is used as follows:

```reasonligo group=big_maps
let updated_map : register =
  Map.remove (("tz1gjaF81ZRRvdzjobyfVNsAeSC6PScjfQwN": address), moves)
```

</Syntax>
