Functional Programming Language with Dependent Types

LTS Haskell 7.20:0.12.3
Stackage Nightly 2016-09-14:0.12.2
Latest on Hackage:0.99.2
BSD3 licensed by Edwin Brady
Maintained by Edwin Brady

Module documentation for 0.12.3


Build Status Appveyor build Documentation Status Hackage Stackage LTS Stackage Nightly IRC

Idris ( is a general-purpose functional programming language with dependent types.

Installation Guides.

This repository represents the latest development version of the language, and may contain bugs that are being actively worked on. For those who wish to use a more stable version of Idris please consider installing the latest version that has been released on Hackage. Installation instructions for various platforms can be found on the Idris Wiki.

More information about building Idris from source has been detailed in the Installation Guide

Code Generation

Idris has support for external code generators. Supplied with the distribution is a C code generator to compile executables, and a JavaScript code generator with support for node.js and browser JavaScript.

At this moment in time there are two external repositories with a Java code generator and an LLVM-based code generator.

More Information

If you would like to find out more information, or ask questions, we currently have a Wiki; a mailing list, and an IRC channel #idris on freenode. To join the IRC channel, point your irc client to then /join #idris.

For those further interested in using Idris for projects, the Idris Hackers GitHub organisation is where some interesting projects are being hosted.

For those interested in contributing to Idris directly we kindly ask that prospective developers please consult the Contributing Guide first.


New in 0.99.2

Library Updates

  • Added Data.Buffer to base. This allows basic manipulation of mutable buffers of Bits8, including reading from and writing to files.

Tool Updates

  • Idris now checks the list of packages specified at the command line against those installed. If there is a mismatch Idris will complain.

Miscellaneous Updates

  • Documentation updates for the new Control.ST library
  • Various stability/efficiency fixes

New in 0.99.1:

Language updates

  • Language pragmas now required for the less stable existing features, in addition to the existing TypeProviders and ErrorReflection: + ElabReflection, which must be enabled to use %runElab + UniquenessTypes, which must be enabled to use UniqueType + DSLNotation, which must be enabled to define a dsl block + FirstClassReflection, which must be enabled to define a %reflection function

  • New language extension LinearTypes: + This allows adding a /multiplicity/ to a binder which says how often it is allowed to be used; either 0 or 1 (if unstated, multiplicity is "many") + The typing rules follow Conor McBride's paper "I Got Plenty o' Nuttin'" + This is highly experimental, unfinished, not at all polished. and there are still lots of details to sort out. Some features don't quite work properly yet. But it is there to play with for the brave!

Tool Updates

  • Idris' output has been updated to more accurately reflect its progress through the compiler i.e. Type Checking; Totality Checking; IBC Generation; Compiling; and Code Generation. To control the loudness of the reporting three verbosity levels are introduced: --V0, --V1, and --V2. The old aliases of -V and --verbose persist.

  • New REPL command :! that runs an external shell command.

  • The REPL now colourises output on MinTTY consoles (e.g., Cygwin and MSYS) on Windows, which previously did not occur due to a bug.

  • Idris now runs in a UTF-8-compatible codepage on Windows. This fixes many Unicode-rendering issues on Windows (e.g., error messages stating commitBuffer: invalid argument (invalid character)).

  • Idris now has a --warnipkg flag to enable auditing of Idris packages during build time. Currently auditing check's the list of modules specified in the iPKG file with those presented in the package directory.

Library Updates

  • Terminating programs has been improved with more appropriate functions (exitWith, exitFailure, and exitSuccess) and a data structure (ExitCode) to capture a program's return code.
  • Casting a String to an Int, Integer or a Double now ignores leading and trailing whitespace. Previously only leading whitespace was ignored.
  • RTS functions openFile, do_popen, and ARGV are now properly encoded using UTF-8 on Windows.

New in 0.99:

Language updates

  • record syntax now allows updating fields, including nested fields, by applying a function using the $= operator. For example:

    record Score where
           constructor MkScore
           correct : Nat
           attempted : Nat
    record GameState where
           constructor MkGameState
           score : Score
           difficulty : Nat
    correct : GameState -> GameState
    correct st = record { score->correct $= (+1),
                          score->attempted $= (+1) } st
  • Implicit parameter to interfaces are now allowed. For example:

    interface Shows (ts : Vect k Type) where
      shows : HVect ts -> Vect k String

    In this interface, k is an implicit parameter, but previously needed to be explicit

Library updates

  • The File Effect has been updated to take into account changes in Prelude.File and to provide a 'better' API.
  • natEnumFromThen and natEnumFromTo have been updated to correctly calculate reverse ranges. Range syntax [a,b..c] now can be used again to generate reverse ranges.
  • divBN and modBN now can only be used for unsigned numbers.
  • return, which has been an alias for pure for many releases, is now deprecated.
  • Replace instance with implementation: + InstanceN is deprecated, use ImplementationN instead. + InstanceCtorN is deprecated, use ImplementationCtorN instead. + addInstance is deprecated, use addImplementation instead. + %instance keyword is deprecated, use %implementation instead.
  • Idris packages are now installed within a sub-directory libs of Idris' data directory, before they were installed in the directory's root.

Tool updates

  • Idris' documentation system now displays the documentation for auto implicits in the output of :doc. This is tested for in docs005.
  • New command line flag --info that displays information about the installation.
  • New command line flag --sourcepath <dir> that allows adding directories to the source search path.
  • Allow 'installation' of a package's IdrisDoc documentation into a central location. The default location is the subdirectory docs of Idris' data directory. New flag --installdoc <ipkg> provided to install documentation New flag --docdir provided to show default documentation installation location. * New environment variable IDRIS_DOC_PATH to allow specification of an alternative installation path for documentation.
  • Semantic meaning behind several environment variables has been clarified in documentation and code. See compilation section of the reference manual for more details.
  • Interface parameter constraints are now printed in the output of :doc. This is tested for in docs006.

Miscellaneous updates

  • New, faster, better, implementation of the coverage checker
  • The test suite now uses tasty-golden. New tests must be registered in test/TestData.hs, as explained in the relevant
  • Added OSX and Windows continous integration with Travis and Appveyor.

UI Changes

  • The :e command can now handle an $EDITOR with arguments in it, like "emacs -nw"

New in 0.12:

Language updates

  • rewrite can now be used to rewrite equalities on functions over dependent types
  • rewrite can now be given an optional rewriting lemma, with the syntax rewrite [rule] using [rewrite_lemma] in [scope].
  • Reorganised elaboration of implementation, so that interfaces with dependencies between methods now work more smoothly
  • Allow naming of parent implementations when defining an implementation. For example:

    [PlusNatSemi] Semigroup Nat where
      (<+>) x y = x + y
    [MultNatSemi] Semigroup Nat where
      (<+>) x y = x * y
    -- use PlusNatSemi as the parent implementation
    [PlusNatMonoid] Monoid Nat using PlusNatSemi where
      neutral = 0
    -- use MultNatSemi as the parent implementation
    [MultNatMonoid] Monoid Nat using MultNatSemi where
      neutral = 1
  • Interface definitions can now include data declarations (but not data definitions). Any implementation of the interface must define the method using a data type. The effect is to cause Idris to treat the method as a data type (for unification and interface resolution purposes).
  • Experimentally, allow named implementations to be available by default in a block of declarations with using notation. For example:

    using implementation PlusNatMonoid
      test : Nat -> Nat
      test x = x <+> x <+> neutral
  • Constraint arguments can now appear anywhere in function types, not just at the top level or after an implicit argument binding.
  • Experimental extended with syntax, which allows calling functions defined in a with block directly. For example:

    data SnocList : List a -> Type where
         Empty : SnocList []
         Snoc : SnocList xs -> SnocList (xs ++ [x])
    snocList : (xs : List a) -> SnocList a
    my_reverse : List a -> List a
    my_reverse xs with (snocList xs)
      my_reverse [] | Empty = []
      my_reverse (ys ++ [x]) | (Snoc p) = x :: my_reverse ys | p

    The | p on the right hand side means that the with block function will be called directly, so the recursive structure of SnocList can direct the recursion structure of my_reverse.

  • Added %fragile directive, which gives a warning and a message when a fragile name is referenced. For use in detailing fragile APIs.
  • The totality checker now looks under case blocks, rather than treating them as mutually defined functions with their top level function, meaning that it can spot more total functions.
  • The totality checker now looks under if...then...else blocks when checking for productivity.
  • The %assert_total directive is now deprecated. Instead, you can use one of the functions assert_total, assert_smaller or assert_unreachable to describe more precisely where a totality assertion is needed.

Library updates

  • Control.WellFounded module removed, and added to the Prelude as Prelude.WellFounded.
  • Added Data.List.Views with views on List and their covering functions.
  • Added Data.Nat.Views with views on Nat and their covering functions.
  • Added Data.Primitives.Views with views on various primitive types and their covering functions.
  • Added System.Concurrency.Sessions for simple management of conversations between processes

iPKG Updates

  • Taking cues from cabal, the iPKG format has been extended to include more package metadata information. The following fields have been added:

    • brief: Brief description of the package.
    • version: Version string to associate with the package.
    • readme: Location of the README file.
    • license: Description of the licensing information.
    • author: Author information.
    • maintainer: Maintainer information.
    • homepage: Website associated with the package.
    • sourcepage: Location of the DVCS where the source can be found.

Miscellaneous updates

  • The Idris man page is now installed as part of the cabal/stack build process.

  • Improved startup performance by reducing the processing of an already imported module that has changed accessibility.

  • A limited set of command line options can be used to override package declared options. Overridable options are currently, logging level and categories, default totality check, warn reach, IBC output folder, and idris path. Note overriding IBC output folder, only affects the installation of Idris packages.

  • Remove deprecated options --ideslave and --ideslave-socket. These options were replaced with --ide-mode and --ide-mode-socket in 0.9.17

  • The code generator output type MavenProject was specific to the Java codegen and has now been deprecated, together with the corresponding --mvn option.

  • Definitional equality on Double is now bit-pattern identity rather than IEEE's comparison operator. This prevents a bug where programs could distinguish between -0.0 and 0.0, but the type theory could not, leading to a contradiction. The new fine-grained equality prevents this.

  • Naming conventions for Idris packages in an iPKG file now follow the same rules for executables. Unquoted names must be valid namespaced Idris identifiers e.g. package my.first.package. Quoted package names allow for packages to be given valid file names, for example, package "my-first-package".

Reflection changes

  • The implicit coercion from String to TTName was removed.

  • Decidable equality for TTName is available.

New in 0.11

Updated export rules

  • The export rules are: - 'private' means that the definition is not exported at all - 'export' means that the top level type is exported, but not the definition. In the case of 'data', this means the type constructor is exported but not the data constructors. - 'public export' means that the entire definition is exported.
  • By default, names are 'private'. This can be altered with an %access directive as before.
  • Exported types can only refer to other exported names
  • Publicly exported definitions can only refer to publicly exported names

Improved C FFI

  • Idris functions can now be passed as callbacks to C functions or wrapped in a C function pointer.
  • C function pointers can be called.
  • Idris can access pointers to C globals.


  • Effects can now be given in any order in effect lists (there is no need for the ordering to be preserved in sub lists of effects)

Elaborator reflection updates

  • Datatypes can now be defined from elaborator reflection: - declareDatatype adds the type constructor declaration to the context - defineDatatype adds the constructors to the datatype - To declare an inductive-recursive family, declare the types of the function and the type constructor before defining the pattern-match cases and constructors.

Minor language changes

  • The [static] annotation is changed to %static to be consistent with the other annotations.
  • Added %auto_implicits directive. The default is %auto_implicits on. Placing %auto_implicits off in a source file means that after that point, any implicit arguments must be bound, e.g.:

    append : {n,m,a:_} -> Vect n a -> Vect m a -> Vect (n + m) a

    Only names which are used explicitly in the type need to be bound, e.g.:

    Here  : {x, xs : _} -> Elem x (x :: xs)

    In Here, there is no need to bind any of the variables in the type of xs (it could be e.g. List a or Vect n a; a and n will still be implicitly bound).

    You can still implicitly bind with 'using':

    ` using (xs : Vect _ _) data Elem : {a, n : _} -> a -> Vect n a -> Type where Here : {x : _} -> Elem x (x :: xs) There : {x, y : _} -> Elem x xs -> Elem x (y :: xs) `

    However, note that only names which appear in both the using block and the type being defined will be implicitly bound. The following will therefore fail because 'n' isn't implicitly bound:

      using (xs : Vect n a)
        bad : Elem x xs -> Elem x (y :: xs)
  • Sigma has been renamed to DPair.
  • Accessor functions for dependent pairs have been renamed to bring them into line with standard accessor functions for pairs. The function getWitness is now fst, and getProof is snd.
  • File Modes expanded: Append, ReadWriteTruncate, and ReadAppend added, Write is deprecated and renamed to WriteTruncate.
  • C11 Extended Mode variations added to File Modes.
  • More flexible holes. Holes can now depend on other holes in a term (such as implicit arguments which may be inferred from the definition of the hole).
  • Programs with holes can now be compiled. Attempting to evaluate an expression with a hole results in a run time error.
  • Dependent pairs now can be specified using a telescope-style syntax, without requirement of nesting, e.g. it is possible to now write the following:

      (a : Type ** n : Nat ** Vect n a)
  • Idris will give a warning if an implicit is bound automatically, but would otherwise be a valid expressio if the name was used as a global

External Dependencies

  • Curses has been removed as an external dependency.

New in 0.10

  • class and instance are now deprecated keywords. They have been replaced by interface and implementation respectively. This is to properly reflect their purpose.
  • (/) operator moved into new Fractional interface.
  • Idris' logging infrastructure has been categorised. Command line and repl are available. For command line the option --logging-categories CATS is used to pass in the categories. Here CATS is a colon separated quoted string containing the categories to log. The REPL command is logcats CATS. Where CATS is a whitespace separated list of categoriese. Default is for all categories to be logged.
  • New flag --listlogcats to list logging categories.

New in 0.9.20

Language updates

  • Improved unification by implementing a pattern unification rule
  • The syntax `{{n}}`` quotes n without resolving it, allowing short syntax for defining new names. {n}` still quotes n to an existing name in scope.
  • A new primitive operator prim__strSubstr for more efficient extraction of substrings. External code generators should implement this.
  • The previous syntax for tactic proofs and the previous interactive prover are now deprecated in favour of reflected elaboration. They will be removed at some point in the future.
  • Changed scoping rules for unbound implicits: any name which would be a valid unbound implicit is now always an unbound implicit. This is much more resilient to changes in inputs, but does require that function names be explicitly qualified when in argument position.
  • Name binding in patterns follows the same rule as name binding for implicits in types: names which begin with lower case letters, not applied to any arguments, are treated as bound pattern variables.
  • Added %deprecate directive, which gives a warning and a message when a deprecated name is referenced.

Library updates

  • The Neg class now represents numeric types which can be negative. As such, the (-) operator and abs have been moved there from Num.
  • A special version of (-) on Nat requires that the second argument is smaller than or equal to the first. minus retains the old behaviour, returning Z if there is an underflow.
  • The (+), (-), and (*) operations on Fin have been removed.
  • New Logging Effects have been added to facilitate logging of effectful programmes.
  • Elaborator reflection is now a part of the prelude. It is no longer necessary to import Language.Reflection.Elab.
  • The PERF effect allows for simple performance metrics to be collected from Effectful programs.
  • Some constructors that never actually occurred have been removed from the TT and Raw reflection datatypes in Language.Reflection.
  • File IO operations (for example openFile/fread/fwrite) now return Either FileError ty where the return type was previously ty to indicate that they may fail.

Tool updates

  • Records are now shown as records in :doc, rather than as the underlying datatype
  • iPKG files have a new option pkgs which takes a comma-separated list of package names that the idris project depends on. This reduces bloat in the opts option with multiple package declarations.
  • iPKG files now allow executable = "your filename here" in addition to the Existing Executable = yourFilenameHere style. While the unquoted version is limited to filenames that look like namespaced Idris identifiers (, the quoted version accepts any valid filename.
  • Add definition command (\d in Vim, Ctrl-Alt-A in Atom, C-c C-s in Emacs) now adds missing clauses if there is already a definition.

Miscellaneous updates

  • Disable the deprecation warnings for %elim and old-style tactic scripts with the --no-elim-deprecation-warnings and --no-tactic-deprecation-warnings flags.

New in 0.9.19

  • The Idris Reference manual has been fleshed out with content originally found on the GitHub wiki.
  • The Show class has been moved into Prelude.Show and augmented with the method showPrec, which allows correct parenthesization of showed terms. This comes with the type Prec of precedences and a few helper functions.
  • New REPL command :printerdepth that sets the pretty-printer to only descend to some particular depth when printing. The default is set to a high number to make it less dangerous to experiment with infinite structures. Infinite depth can be set by calling :printerdepth with no argument.
  • Compiler output shows applications of >>= in do-notation
  • fromInteger i where i is an integer constant is now shown just as i in compiler output
  • An interactive shell, similar to the prover, for running reflected elaborator actions. Access it with :elab from the REPL.
  • New command-line option --highlight that causes Idris to save highlighting information when successfully type checking. The information is in the same format sent by the IDE mode, and is saved in a file with the extension ".idh".
  • Highlighting information is saved by the parser as well, allowing it to highlight keywords like case, of, let, and do.
  • Use predicates instead of boolean equality proofs as preconditions on List functions
  • More flexible 'case' construct, allowing each branch to target different types, provided that the case analysis does not affect the form of any variable used in the right hand side of the case.
  • Some improvements in interactive editing, particularly in lifting out definitions and proof search.
  • Moved System.Interactive, along with getArgs to the Prelude.
  • Major improvements to reflected elaboration scripts, including the ability to run them in a declaration context and many bug fixes.
  • decl syntax rules to allow syntax extensions at the declaration level
  • Experimental Windows support for console colours

New in 0.9.18:

  • GHC 7.10 compatibility
  • Add support for bundled toolchains.
  • Strings are now UTF8 encoded in the default back end
  • Idris source files are now assumed to be in UTF8, regardless of locale settings.
  • Some reorganisation of primitives: + Buffer and BitVector primitives have been removed (they were not tested sufficiently, and lack a maintainer) + Float has been renamed Double (Float is defined in the Prelude for compatibility) + Externally defined primitives and operations now supported with %extern directive, allowing back ends to define their own special purpose primitives + Ptr and ManagedPtr have been removed and replaced with external primitives
  • Add %hint function annotation, which allows functions to be used as hints in proof search for auto arguments. Only functions which return an instance of a data or record type are allowed as hints.
  • Syntax rules no longer perform variable capture. Users of effects will need to explicitly name results in dependent effect signatures instead of using the default name result.
  • Pattern-matching lambdas are allowed to be impossible. For example, Dec (2 = 3) can now be constructed with No $ \(Refl) impossible, instead of requiring a separate lemma.
  • Case alternatives are allowed to be impossible:

    case Vect.Nil {a=Nat} of { (x::xs) impossible ; [] => True }
  • The default Semigroup and Monoid instances for Maybe are now prioritised choice, keeping the first success as Alternative does. The version that collects successes is now a named instance.
  • :exec REPL command now takes an optional expression to compile and run/show
  • The return types of Vect.findIndex, Vect.elemIndex and Vect.elemIndexBy were changed from Maybe Nat to Maybe (Fin n)
  • A new :browse command shows the contents of a namespace
  • `{n} is syntax for a quotation of the reflected representation of the name n. If n is lexically bound, then the resulting quotation will be for it, whereas if it is not, then it will succeed with a quotation of the unique global name that matches.
  • New syntax for records that closely matches our other record-like structures: type classes. See the updated tutorial for details.
  • Records can be coinductive. Define coinductive records with the corecord keyword.
  • Type class constructors can be assigned user-accessible names. This is done using the same syntax as record constructors.
  • if ... then ... else ... is now built-in syntax instead of being defined in a library. It is shown in REPL output and error messages, rather than its desugaring.
  • The desugaring of if ... then ... else ... has been renamed to ifThenElse from boolElim. This is for consistency with GHC Haskell and scala-virtualized, and to reflect that if-notation makes sense with non-Bool datatypes.
  • Agda-style semantic highlighting is supported over the IDE protocol.
  • Experimental support for elaborator reflection. Users can now script the elaborator, for use in code generation and proof automation. This feature is still under rapid development and is subject to change without notice. See Language.Reflection.Elab and the %runElab constructs

New in 0.9.17

  • The --ideslave command line option has been replaced with a --ide-mode command line option with the same semantics.
  • A new tactic claim N TY that introduces a new hole named N with type TY
  • A new tactic unfocus that moves the current hole to the bottom of the hole stack
  • Quasiquotation supports the generation of Language.Reflection.Raw terms in addition to Language.Reflection.TT. Types are used for disambiguation, defaulting to TT at the REPL.
  • Language.Reflection.Quotable now takes an extra type parameter which determines the type to be quoted to. Instances are provided to quote common types to both TT and Raw.
  • Library operators have been renamed for consistency with Haskell. In particular, Applicative.(<$>) is now Applicative.(<*>) and (<$>) is now an alias for Correspondingly, ($>) and (<$) have been renamed to (<*) and (*>). The cascading effects of this rename are that Algebra.(<*>) has been renamed to Algebra.(<.>) and Matrix.(<.>) is now Matrix.(<:>).
  • Binding forms in DSL notation are now given an extra argument: a reflected representation of the name that the user chose. Specifically, the rewritten lambda, pi, and let binders will now get an extra argument of type TTName. This allows more understandable dynamic errors in DSL code and more readable code generation results.
  • DSL notation can now be applied with $
  • Added FFI_Export type which allows Idris functions to be exportoed and called from foreign code
  • Instances can now have documentation strings.
  • Type providers can have documentation strings.
  • Unification errors now (where possible) contain information about provenance of a type
  • New REPL command :core TM that shows the elaborated form of TM along with its elaborated type using the syntax of TT. IDE mode has a corresponding command :elaborate-term for serialized terms.
  • Effectful and IO function names for sending data to STDOUT have been aligned, semantically. + print is now for putting showable things to STDOUT. + printLn is for putting showable things to STDOUT with a new line + putCharLn for putting a single character to STDOUT, with a new line.
  • Classes can now be annotated with 'determining parameters' to say which must be available before resolving instances. Only determining parameters are checked when checking for overlapping instances.
  • New package contrib containing things that are less mature or less used than the contents of base. contrib is not available by default, so you may need to add -p contrib to your .ipkg file or Idris command line.
  • Arguments to class instances are now checked for injectivity. Unification assumes this, so we need to check when instances are defined.

New in 0.9.16

  • Inductive-inductive definitions are now supported (i.e. simultaneously defined types where one is indexed by the other.)
  • Implicits and type class constraints can now appear in scopes other than the top level.
  • Importing a module no longer means it is automatically reexported. A new public modifier has been added to import statements, which will reexport the names exported from that module.
  • Implemented @-patterns. A pattern of the form x@p on the left hand side matches p, with x in scope on the right hand side with value p.
  • A new tactic sourceLocation that fills the current hole with the current source code span, if this information is available. If not, it raises an error.
  • Better Unicode support for the JavaScript/Node codegen
  • :search and :apropos commands can now be given optional package lists to search.
  • Vect, Fin and So moved out of prelude into base, in modules Data.Vect, Data.Fin and Data.So respectively.
  • Several long-standing issues resolved, particularly with pattern matching and coverage checking.
  • Modules can now have API documentation strings.

New in 0.9.15

  • Two new tactics: skip and fail. Skip does nothing, and fail takes a string as an argument and produces it as an error.
  • Corresponding reflected tactics Skip and Fail. Reflected Fail takes a list of ErrorReportParts as an argument, like error handlers produce, allowing access to the pretty-printer.
  • Stop showing irrelevant and inaccessible internal names in the interactive prover.
  • The proof arguments in the List library functions are now implicit and solved automatically.
  • More efficient representation of proof state, leading to faster elaboration of large expressions.
  • EXPERIMENTAL Implementation of uniqueness types
  • Unary negation now desugars to negate, which is a method of the Neg type class. This allows instances of Num that can't be negative, like Nat, and it makes correct IEEE Float operations easier to encode. Additionally, unary negation is now available to DSL authors.
  • The Java and LLVM backends have been factored out for separate maintenance. Now, the compiler distribution only ships with the C and JavaScript backends.
  • New REPL command :printdef displays the internal definition of a name
  • New REPL command :pprint pretty-prints a definition or term with LaTeX or HTML highlighting
  • Naming of data and type constructors is made consistent across the standard library (see #1516)
  • Terms in code blocks inside of documentation strings are now parsed and type checked. If this succeeds, they are rendered in full color in documentation lookups, and with semantic highlighting for IDEs.
  • Fenced code blocks in docs defined with the "example" attribute are rendered as code examples.
  • Fenced code blocks declared to be Idris code that fail to parse or type check now provide error messages to IDE clients.
  • EXPERIMENTAL support for partial evaluation (Scrapping your Inefficient Engine style)

New in 0.9.14

  • Tactic for case analysis in proofs
  • Induction and case tactic now work on expressions
  • Support for running tests for a package with the tests section of .ipkg files and the --testpkg command-line option
  • Clearly distinguish between type providers and postulate providers at the use site
  • Allow dependent function syntax to be overridden in dsl blocks, similarly to functions and let. The keyword for this is pi.
  • Updated effects library, with simplified API
  • All new JavaScript backend (avoids callstack overflows)
  • Add support for %lib directive for NodeJS
  • Quasiquotes and quasiquote patterns allow easier work with reflected terms. `(EXPR) quasiquotes EXPR, causing the elaborator to be used to produce a reflected version of it. Subterms prefixed with ~ are unquoted - on the RHS, they are reflected terms to splice in, while on the LHS they are patterns.

    A quasiquote expression can be given a goal type for the elaborator, which helps with disambiguation. For instance, `(() : ())`` quotes the unit constructor, while (() : Type)` quotes the unit type. Both goal types and quasiquote are typechecked in the global environment.

  • Better inference of unbound implicits

New in 0.9.13

  • IDE support for retrieving structured information about metavariables
  • Experimental Bits support for JavaScript
  • IdrisDoc: a Haddock- and JavaDoc-like HTML documentation generator
  • Command line option -e (or --eval) to evaluate expressions without loading the REPL. This is useful for writing more portable tests.
  • Many more of the basic functions and datatypes are documented.
  • Primitive types such as Int and String are documented
  • Removed javascript lib in favor of idris-hackers/iQuery
  • Specify codegen for :compile REPL command (e.g. :compile javascript program.js)
  • Remove :info REPL command, subsume and enhance its functionality in the :doc command
  • New (first class) nested record update/access syntax:

    record { a->b->c = val } x -- sets field accessed by c (b (a x)) to val
    record { a->b->c } x -- accesses field, equivalent to c (b (a x))
  • The banner at startup can be suppressed by adding :set nobanner to the initialisation script.
  • :apropos now accepts space-delimited lists of query items, and searches for the conjunction of its inputs. It also accepts binder syntax as search strings - for instance, -> finds functions.
  • Totality errors are now treated as warnings until code generation time, when they become errors again. This allows users to use the interactive editing features to fix totality issues, but no programs that violate the stated assumptions will actually run.
  • Added :makelemma command, which adds a new top level definition to solve a metavariable.
  • Extend :addclause to add instance bodies as well as definitions
  • Reverse parameters to BoundedList -- now matches Vect, and is easier to instantiate classes.
  • Move foldl into Foldable so it can be overridden.
  • Experimental :search REPL command for finding functions by type

Internal changes

  • New implementation of erasure

New in 0.9.12

  • Proof search now works for metavariables in types, giving some interactive type inference.
  • New Lazy type, replacing laziness annotations.
  • JavaScript and Node codegen now understand the %include directive.
  • Concept of null is now understood in the JavaScript and Node codegen.
  • Lots of performance patches for generated JavaScript.
  • New commands :eval (:e) and :type (:t) in the prover, which either normalise or show the type of expressions.
  • Allow type providers to return postulates in addition to terms.
  • Syntax for dealing with match failure in <- and pattern matching let.
  • New syntax for inline documentation. Documentation starts with |||, and arguments are documented by preceding their name with @. Example:

    ||| Add two natural numbers
    ||| @ n the first number (examined by the function)
    ||| @ m the second number (not examined)
    plus (n, m : Nat) -> Nat
  • Allow the auto-solve behaviour in the prover to be disabled, for easier debugging of proof automation. Use :set autosolve and :unset autosolve.
  • Updated effects library
  • New :apropos command at REPL to search documentation, names, and types
  • Unification errors are now slightly more informative
  • Support mixed induction/coinduction with Inf type
  • Add covering function option, which checks whether a function and all descendants cover all possible inputs

New in 0.9.11

  • Agda-style equational reasoning (in Syntax.PreorderReasoning)
  • 'case' construct now abstracts over the scrutinee in its type
  • Added label type 'name (equivalent to the empty type). This is intended for field/effect disambiguation. "name" can be any valid identifier. Two labels are definitionally equal if they have the same name.
  • General improvements in error messages, especially %error_reverse annotation, which allows a hint as to how to display a term in error messages
  • --ideslave mode now transmits semantic information about many of the strings that it emits, which can be used by clients to implement semantic highlighting like that of the REPL. This has been implemented in the Emacs mode and the IRC bot, which can serve as examples.
  • New expression form: with NAME EXPR privileges the namespace NAME when disambiguating overloaded names. For example, it is possible to write with Vect [1,2,3] at the REPL instead of the (Vect _ _) [1,2,3], because the Vect constructors are defined in a namespace called Vect.
  • assert_smaller internal function, which marks an expression as smaller than a pattern for use in totality checking. e.g. assert_smaller (x :: xs) (f xs) asserts that f xs will always be structurally smaller than (x :: xs)
  • assert_total internal function, which marks a subexpression as assumed to be total, e.g assert_total (tail (x :: xs)).
  • Terminal width is automatically detected if Idris is compiled with curses support. If curses is not available, automatic mode assumes 80 columns.
  • Changed argument order for Prelude.Either.either.
  • Experimental neweffects'library, intended to replace effects in the next release.

Internal changes

  • Faster elaboration
  • Smaller .ibc files
  • Pretty-printer now used for all term output

New in 0.9.10

  • Type classes now implemented as dependent records, meaning that method types may now depend on earlier methods.
  • More flexible class instance resolution, so that function types and lambda expressions can be made instances of a type class.
  • Add !expr notation for implicit binding of intermediate results in monadic/do/etc expressions.
  • Extend Effects package to cope with possibly failing operations, using if_valid, if_error, etc.
  • At the REPL, it now refers to the previous expression.
  • Semantic colouring at the REPL. Turn this off with --nocolour.
  • Some prettifying of error messages.
  • The contents of ~/.idris/repl/init are run at REPL start-up.
  • The REPL stores a command history in ~/.idris/repl/history.
  • The [a..b], [a,b..c], [a..], and [a,b..] syntax now pass the totality checker and can thus be used in types. The [x..] syntax now returns an actually infinite stream.
  • Add %reflection option for functions, for compile-time operations on syntax.
  • Add expression form quoteGoal x by p in e which applies p to the expected expression type and binds the result to x in the scope e.
  • Performance improvements in Strings library.
  • Library reorganisation, separated into prelude/ and base/.

Internal changes

  • New module/dependency tree checking.
  • New parser implementation with more precise errors.
  • Improved type class resolution.
  • Compiling Nat via GMP integers.
  • Performance improvements in elaboration.
  • Improvements in termination checking.
  • Various REPL commands to support interactive editing, and a client/server mode to allow external invocation of REPL commands.

New in 0.9.9

User visible changes

  • Apply functions by return type, rather than with arguments: t <== f means "apply f with arguments such that it returns a value of type t"
  • Allow the result type of a rewrite to be specified
  • Allow names to be attached to provisional definitions lhs ?= {name} rhs -- generates a lemma called name which makes the types of the lhs and rhs match. {name} is optional - a unique name is generated if it is absent.
  • Experimental LLVM backend
  • Added Data.HVect module
  • Fix fromInteger to take an Integer, rather than an Int
  • Integer literals for Fin
  • Renamed O to Z, and fO to fZ
  • Swapped Vect arguments, now Vect : Nat -> Type -> Type
  • Added DecEq instances
  • Add equiv tactic, which rewrites a goal to an equivalent (convertible) goal

Internal changes

  • Add annotation for unification traces
  • Add mrefine tactic for refining by matching against a type
  • Type class resolution fixes
  • Much faster coverage checking

New in 0.9.8

User visible changes

  • Added rewrite ... in ... construct
  • Allow type class constraints in using clauses
  • Renamed EFF to EFFECT in Effect package
  • Experimental Java backend
  • Tab completion in REPL
  • Dynamic loading of C libraries in the interpreter
  • Testing IO actions at the REPL with :x command
  • Improve rendering of :t
  • Fixed some INTERNAL ERROR messages

Internal Changes

  • Fix non-linear pattern checking
  • Improved name disambiguation
  • More flexible unification and elaboration of lambdas
  • Various unification and totality checking bug fixes

New in 0.9.7

User visible changes

  • implicit keyword, for implicit type conversion
  • Added Effects package
  • Primitives for 8,16,32 and 64 bit integers

Internal Changes

  • Change unification so that it keeps track of failed constraints in case later information helps to resolve them
  • Distinguishing parameters and indices in data types
  • Faster termination/coverage checking
  • Split 'javascript' target into 'javascript' and 'node'

New in 0.9.6

User visible changes

  • The type of types is now Type rather than Set
  • Forward declarations of data allowed - supporting induction recursion and mutually recursive data
  • Type inference of definitions in where clauses - Provided that the type can be completely determined from the first application of the function (in the top level definition)
  • mutual blocks added - effect is to elaborate all types of declarations in the block before elaborating their definitions - allows inductive-recursive definitions
  • Expression inspected by with clause now abstracted from the goal - i.e. "magic" with
  • Implicit arguments will be added automatically only if their initial letter is lower case, or they are in a using declaration
  • Added documentation comments (Haddock style) and :doc REPL command
  • Pattern matching on strings, big integers and characters
  • Added System.Concurrency modules
  • Added postulate declarations
  • Allow type annotations on let tactic
  • EXPERIMENTAL JavaScript generation, with --target javascript option

Internal Changes

  • Separate inlining methods at compile-time and run-time
  • Fixed nested parameters blocks
  • Improve efficiency of elaborator by: - only normalising when necessary - reducing backtracking with resolving ambiguities
  • Better compilation of case trees

New in 0.9.5

User visible changes

  • Added codata - as data declarations, but constructor arguments are evaluated lazily - functions which return a codata type do not reduce at compile time
  • Added parameters blocks
  • Allow local data definitions in where blocks
  • Added %default directive to declare total-by-default or partial-by-default for functions, and a corresponding "partial" reserved words to mark functions as allowed to be partial. Also --total and --partial added as command line options.
  • Command line option --warnpartial for flagging all undeclared partial functions, without error.
  • New termination checker supporting mutually recursive definitions.
  • Added :load command to REPL, for loading a new file
  • Added :module command to REPL, for adding modules
  • Renamed library modules (now have initial capital)

Internal changes

  • Several improvements and fixes to unification
  • Added collapsing optimisation and more aggressive erasure

New in 0.9.4:

User visible changes

  • Simple packaging system
  • Added --dumpc flag for displaying generated code

Internal changes

  • Improve overloading resolution (especially where this is a type error)
  • Various important bug fixes with evaluation and compilation
  • More aggressive compile-time evaluation

New in 0.9.3

User visible changes

  • Added binding forms to syntax rules
  • Named class instances
  • Added :set command, with options errorcontext for displaying local variables in scope when a unification error occurs, and showimplicits for displaying elaborated terms in full
  • Added --errorcontext command line switch
  • Added :proofs and :rmproofs commands
  • Various minor REPL improvements and fixes

Internal changes

  • Completely new run time system (not based on Epic or relying on Boehm GC)
  • Normalise before forcing to catch more forceable arguments
  • Types no longer exported in normal form
  • Try to resolve overloading by inspecting types, rather than full type checking

New in 0.9.2

User visible changes

  • backtick notation added: x `foo` y ==> foo x y
  • case expressions allowed in type signatures
  • Library extensions in prelude.vect and prelude.algebra
  • malloc/trace_malloc added to builtins.idr

Internal changes

  • Some type class resolution fixes
  • Several minor bug fixes
  • Performance improvements in resolving overloading and type classes

New in 0.9.1

User visible changes

  • DSL notation, for overloading lambda and let bindings
  • Dependent records, with projection and update
  • Totality checking and total keyword
  • Auto implicits and default argument values {auto n : T}, {default val n : T}
  • Overlapping type class instances disallowed
  • Many extensions to prelude.nat and prelude.list libraries (mostly thanks to Dominic Mulligan)
  • New libraries: control.monad.identity, control.monad.state
  • Small improvements in error reporting

Internal changes

  • Faster compilation (only compiling names which are used)
  • Better type class resolution
  • Lots of minor bug fixes

0.1.x to 0.9.0

Complete rewrite.

User visible changes

  • New proof/tactics syntax
  • New syntax for pairs/dependent pairs
  • Indentation-significant syntax
  • Added type classes
  • Added where clauses
  • Added case expressions, pattern matching let and lambda
  • Added monad comprehensions
  • Added cumulativity and universe checking
  • Ad-hoc name overloading - Resolved by type or explicit namespace
  • Modules (Haskell-style)
  • public, abstract and private access to functions and types
  • Separate type-checking
  • Improved interactive environment
  • Replaced 'do using' with Monad class
  • Extended syntax macros

Internal changes

  • Everything :-)
  • All definitions (functions, classes and instances) are elaborated to top level, fully explicit, data declarations and pattern matching definitions, which are verified by a minimal type checker.

This is the first release of a complete reimplementation. There will be bugs. If you find any, please do not hesitate to contact Edwin Brady (

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