Info about the unit type (#401)

* Info about the unit type

* Move unit to complex types

* Add note on where to get all types for languages

* Clarify

* Examples of the unit type

* Don't define unit as a case of option

docs/smart-contracts/data-types/complex-data-types.md

@@ -2,7 +2,7 @@
 title: Complex data types
 authors: 'Mathias Hiron (Nomadic Labs), Sasha Aldrick (TriliTech), Tim McMackin (TriliTech)'
 last_update:
-  date: 5 October 2023
+  date: 17 June 2024
 ---
 
 Tezos contracts support these complex data types.
@@ -17,6 +17,15 @@ The high-level languages may implement these data types slightly differently, bu
 - [Variants and Unions](#variants)
 - [Lambdas](#lambdas)
 - [Tickets](#tickets)
+- [Unit](#unit)
+
+This list is intended for general information for developers and is not intended to be comprehensive.
+For a complete list of data types that are available, see the reference information for the language that you are using:
+
+- Michelson: [Types](https://tezos.gitlab.io/michelson-reference/#types)
+- LIGO: [Introduction](https://ligolang.org/docs/intro/introduction?lang=jsligo)
+- Archetype: [Types](https://archetype-lang.org/docs/reference/types)
+- SmartPy: [Overview](https://smartpy.io/manual/syntax/overview)
 
 ## Pairs {#pairs}
 
@@ -456,3 +465,28 @@ Contracts can run these operations on tickets:
 - LIGO: [Tickets](https://ligolang.org/docs/reference/current-reference#tickets)
 - Archetype: [create_ticket and related](https://archetype-lang.org/docs/reference/expressions/builtins/#create_ticket%28s%20:%20T,%20n%20:%20nat%29)
 - SmartPy: [Tickets](https://smartpy.io/manual/syntax/tickets)
+
+## Unit {#unit}
+
+In Tezos, the `unit` type contains a single value that holds no information.
+Smart contracts use unit values as placeholders where a variable is required but no other information is needed.
+It is the input type of functions taking no input, the output type of functions producing no output, and the storage type of contracts storing no information.
+
+For example, if a LIGO entrypoint receives no parameter, the data type of the entrypoint's parameter is `unit`:
+
+```jsligo
+@entry
+const myentrypoint = (_unusedParameter: unit, store: storageType): returnType => {
+  // ...
+}
+```
+
+Similarly, if you call this entrypoint with the Octez client and omit the `--arg` argument to pass no parameter, the client passes unit in the background.
+
+Unit is a concept that Tezos inherits from OCaml; see [Side-Effects and the unit Type](https://ocaml.org/docs/tour-of-ocaml#side-effects-and-the-unit-type) in the OCaml documentation.
+
+### Implementation details
+
+- LIGO: [Unit](https://ligolang.org/docs/variants/unit/?lang=jsligo)
+- Archetype: [Unit](https://archetype-lang.org/docs/reference/types/#unit)
+- SmartPy: [Unit](https://smartpy.io/manual/syntax/unit)

docs/smart-contracts/data-types/primitive-data-types.md

@@ -2,7 +2,7 @@
 title: Primitive data types
 authors: 'Mathias Hiron (Nomadic Labs), Sasha Aldrick (TriliTech), Tim McMackin (TriliTech)'
 last_update:
-  date: 4 October 2023
+  date: 4 June 2024
 ---
 
 Tezos contracts support these primitive data types.
@@ -16,6 +16,14 @@ The high-level languages may implement these data types slightly differently, bu
 - [Timestamps](#timestamps)
 - [Addresses](#addresses)
 
+This list is intended for general information for developers and is not intended to be comprehensive.
+For a complete list of data types that are available, see the reference information for the language that you are using:
+
+- Michelson: [Types](https://tezos.gitlab.io/michelson-reference/#types)
+- LIGO: [Introduction](https://ligolang.org/docs/intro/introduction?lang=jsligo)
+- Archetype: [Types](https://archetype-lang.org/docs/reference/types)
+- SmartPy: [Overview](https://smartpy.io/manual/syntax/overview)
+
 ## Numeric data types: `int` and `nat` {#numeric}
 
 Integers (`int`) are whole numbers that can be positive or negative.