mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-26 21:23:53 +03:00
76 lines
3.1 KiB
ReStructuredText
76 lines
3.1 KiB
ReStructuredText
.. _sect-intro:
|
||
|
||
************
|
||
Introduction
|
||
************
|
||
|
||
In conventional programming languages, there is a clear distinction
|
||
between *types* and *values*. For example, in `Haskell
|
||
<https://www.haskell.org>`_, the following are types, representing
|
||
integers, characters, lists of characters, and lists of any value
|
||
respectively:
|
||
|
||
- ``Int``, ``Char``, ``[Char]``, ``[a]``
|
||
|
||
Correspondingly, the following values are examples of inhabitants of
|
||
those types:
|
||
|
||
- ``42``, ``’a’``, ``"Hello world!"``, ``[2,3,4,5,6]``
|
||
|
||
In a language with *dependent types*, however, the distinction is less
|
||
clear. Dependent types allow types to “depend” on values — in other
|
||
words, types are a *first class* language construct and can be
|
||
manipulated like any other value. The standard example is the type of
|
||
lists of a given length [#fn1]_, ``Vect n a``, where ``a`` is the element
|
||
type and ``n`` is the length of the list and can be an arbitrary term.
|
||
|
||
When types can contain values, and where those values describe
|
||
properties, for example the length of a list, the type of a function
|
||
can begin to describe its own properties. Take for example the
|
||
concatenation of two lists. This operation has the property that the
|
||
resulting list's length is the sum of the lengths of the two input
|
||
lists. We can therefore give the following type to the ``app``
|
||
function, which concatenates vectors:
|
||
|
||
.. code-block:: idris
|
||
|
||
app : Vect n a -> Vect m a -> Vect (n + m) a
|
||
|
||
This tutorial introduces Idris, a general purpose functional
|
||
programming language with dependent types. The goal of the Idris
|
||
project is to build a dependently typed language suitable for
|
||
verifiable general purpose programming. To this end, Idris is a compiled
|
||
language which aims to generate efficient executable code. It also has
|
||
a lightweight foreign function interface which allows easy interaction
|
||
with external libraries.
|
||
|
||
Intended Audience
|
||
=================
|
||
|
||
This tutorial is intended as a brief introduction to the language, and
|
||
is aimed at readers already familiar with a functional language such
|
||
as `Haskell <https://www.haskell.org>`_ or `OCaml <https://ocaml.org>`_.
|
||
In particular, a certain amount of familiarity with Haskell syntax is
|
||
assumed, although most concepts will at least be explained
|
||
briefly. The reader is also assumed to have some interest in using
|
||
dependent types for writing and verifying software.
|
||
|
||
For a more in-depth introduction to Idris, which proceeds at a much slower
|
||
pace, covering interactive program development, with many more examples, see
|
||
`Type-Driven Development with Idris <https://www.manning.com/books/type-driven-development-with-idris>`_
|
||
by Edwin Brady, available from `Manning <https://www.manning.com>`_.
|
||
|
||
Example Code
|
||
============
|
||
|
||
This tutorial includes some example code, which has been tested
|
||
against Idris 2. These files are available with the Idris 2 distribution,
|
||
so that you can try them out easily. They can be found under
|
||
``samples``. It is, however, strongly recommended that you type
|
||
them in yourself, rather than simply loading and reading them.
|
||
|
||
.. rubric:: Footnotes
|
||
|
||
.. [#fn1] Typically, and perhaps confusingly, referred to in the dependently
|
||
typed programming literature as "vectors".
|