Idris (programming language)

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Idris (programming language)
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Agda (programming language)>Agda, Clean (programming language),"UNIQUENESS TYPES"ACCESSDATE=2018-11-20, Coq,IDRIS, A LANGUAGE WITH DEPENDENT TYPES>URL=HTTP://WWW.IDRIS-LANG.ORG/Epigram (programming language)>Epigram, Haskell (programming language), ML (programming language)>ML, Rust| influenced =| operating_system = Cross-platform| license = BSD-3| file ext = .idr,}}}}Idris is a general-purpose purely functional programming language with dependent types, optional lazy evaluation, and features such as a totality checker.Idris may be used to prove mathematical theorems, but it is primarily designed to be a general-purpose programming language like Haskell. The type system is similar to Agda, and proofs are similar to Coq, including tactics. Compared to Agda and Coq, Idris prioritizes management of side effects and support for embedded domain-specific languages.Idris compiles to C (relying on a custom copying garbage collector using Cheney's algorithm) and JavaScript (both browser- and Node.js-based). There are several third-party code generators for other platforms, including LLVM, JVM, and CIL.WEB,weblink Code Generation Targets — Idris 1.1.1 documentation,, Idris is named after a singing dragon from the 1970s UK children's television program Ivor the Engine.WEB, Frequently Asked Questions,weblink 2015-07-19,


Idris combines a number of features from relatively mainstream functional programming languages with features borrowed from proof assistants.

Functional programming

The syntax of Idris shows many similarities with that of Haskell. A hello world program in Idris might look like this:module Mainmain : IO ()main = putStrLn "Hello, World!"The only differences between this program and its Haskell equivalent are the single colon (instead of two) in the signature of the main function and the omission of the word "where" in the module declaration.

Inductive and parametric data types

Idris supports inductively-defined data types and parametric polymorphism. Such types can be defined both in traditional "Haskell98" syntax:data Tree a = Node (Tree a) (Tree a) | Leaf aor in the more general GADT syntax:data Tree : Type -> Type where
Node : Tree a -> Tree a -> Tree a
Leaf : a -> Tree a

Dependent types

With dependent types, it is possible for values to appear in the types; in effect, any value-level computation can be performed during typechecking. The following defines a type of lists of statically known length, traditionally called 'vectors':data Vect : Nat -> Type -> Type where
Nil : Vect 0 a
(::) : (x : a) -> (xs : Vect n a) -> Vect (n + 1) a
This type can be used as follows:totalappend : Vect n a -> Vect m a -> Vect (n + m) aappend Nil ys = ysappend (x :: xs) ys = x :: append xs ysThe functions append a vector of m elements of type a to a vector of n elements of type a. Since the precise types of the input vectors depend on a value, it is possible to be certain at compile-time that the resulting vector will have exactly (n + m) elements of type a.The word "total" invokes the totality checker which will report an error if the function doesn't cover all possible cases or cannot be (automatically) proven not to enter an infinite loop.Another common example is pairwise addition of two vectors that are parameterized over their length:totalpairAdd : Num a => Vect n a -> Vect n a -> Vect n apairAdd Nil Nil = NilpairAdd (x :: xs) (y :: ys) = x + y :: pairAdd xs ysNum a signifies that the type a belongs to the type class Num. Note that this function still typechecks successfully as total, even though there is no case matching Nil in one vector and a number in the other. Since both vectors are ensured by the type system to have exactly the same length, we can be sure at compile time that this case will not occur. Hence it does not need to be mentioned for the function to be total.

Proof assistant features

Dependent types are powerful enough to encode most properties of programs, and an Idris program can prove invariants at compile-time. This makes Idris into a proof assistant.There are two standard ways of interacting with proof assistants: by writing a series of tactic invocations (Coq style), or by interactively elaborating a proof term (Epigram/Agda style). Idris supports both modes of interaction, although the set of available tactics is not yet as useful as that of Coq.

Code generation

Because Idris contains a proof assistant, Idris programs can be written to pass proofs around. If treated naïvely, such proofs remain around at runtime. Idris aims to avoid this pitfall by aggressively erasing unused terms,WEB,weblink Erasure By Usage Analysis — Idris 1.1.1 documentation,, with promising{{Vague|date=May 2018}} results.WEB,weblink Benchmark results,, By default, Idris generates native code through C. The other officially supported backend generates JavaScript.

See also



External links

{{Programming languages}}

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- "Idris (programming language)" does not exist on GetWiki (yet)
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M.R.M. Parrott