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| id | title |
|---|---|
| introduction | Introduction To LIGO |
LIGO is a programming language for writing Tezos smart contracts.
The LIGO philosophy can be described in a few bullet points:
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Design a clean, simple language with no unnecessary parts.
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Give that language multiple syntaxes borrowed from other languages. Ideally LIGO requires the user to learn almost no new syntax.
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Have that simple language encourage people to write simple code, so that it's easy to formally verify the compiled output using a project like Mi-Cho-Coq.
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Stop waking up in the morning to find that your smart contract lost all its money to some stupid exploit.
The current trend in language design is more, more, more, so this might seem counterintuitive. However most useful smart contracts can express their core functionality in under a thousand lines of code. The problem domain necessitates that you get as close as possible to the minimal code size and resource use. LIGO is a functional language designed to include the features you need, while avoiding patterns that make formal verification hard.
For example LIGO doesn't use an object oriented paradigm, currently code is organized using functions. While LIGO plans to have a module system in the future, we don't want programs to have thousands of dependencies. Once a contract is put on the blockchain, it's not possible to change it. A new version can be uploaded, but the original contract remains available. Contracts tend to control money. In that environment it's not responsible to encourage users to incorporate lots of code from strangers. The immutability of contracts make formal verification of contract logic attractive. The eventual goal is to make it easy to compile a LIGO contract to a format that can be loaded into the Coq proof assistant.
LIGO for Programming Smart Contracts on Tezos
Perhaps the most striking feature of LIGO is that it comes in different concrete syntaxes, and even different programming paradigms. In other words, LIGO is not defined by one syntax and one paradigm, like imperative versus functional.
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There is PascaLIGO, which is inspired by Pascal, hence is an imperative language with lots of keywords, where values can be locally mutated after they have been annotated with their types (declaration).
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There is CameLIGO, which is inspired by the pure subset of OCaml, hence is a functional language with few keywords, where values cannot be mutated, but still require type annotations (unlike OCaml, whose compiler performs almost full type inference).
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There is ReasonLIGO, which is inspired by the pure subset of ReasonML, which is based upon OCaml.
Let's define some LIGO contract in the three flavours above. Do not worry if it is a little confusing at first; we will explain all the syntax in the upcoming sections of the documentation.
type storage is int
type parameter is
Increment of int
| Decrement of int
| Reset
type return is list (operation) * storage
function main (const action : parameter; const store : storage) : return is
((nil : list (operation)),
case action of
Increment (n) -> store + n
| Decrement (n) -> store - n
| Reset -> 0
end)
type storage = int
type parameter =
Increment of int
| Decrement of int
| Reset
type return = operation list * storage
let main (action, store : parameter * storage) : return =
([] : operation list),
(match action with
Increment n -> store + n
| Decrement n -> store - n
| Reset -> 0)
type storage = int;
type parameter =
Increment (int)
| Decrement (int)
| Reset;
type return = (list (operation), storage);
let main = ((action, store): (parameter, storage)) : return => {
(([] : list (operation)),
(switch (action) {
| Increment (n) => store + n
| Decrement (n) => store - n
| Reset => 0}));
};
This LIGO contract accepts the following LIGO expressions:
Increment(n), Decrement(n) and Reset. Those serve as
entrypoint identification.
Runnable code snippets & exercises
Some of the sections in this documentation will include runnable code snippets and exercises. Sources for those are available at the LIGO Gitlab repository.
Snippets
For example code snippets for the Types subsection of this doc, can be found here:
gitlab-pages/docs/language-basics/src/types/**
Exercises
Solutions to exercises can be found e.g. here: gitlab-pages/docs/language-basics/exercises/types/**/solutions/**
Running snippets / exercise solutions
In certain cases it makes sense to be able to run/evaluate the given snippet or a solution, usually there'll be an example command which you can use, such as:
ligo evaluate-value -s pascaligo gitlab-pages/docs/language-basics/src/variables-and-constants/const.ligo age
# Outputs: 25