7Idris comes with a ``REPL``.
12Being a fully dependently typed language, Idris has two phases where it
13evaluates things, compile-time and run-time. At compile-time it will only
14evaluate things which it knows to be total (i.e. terminating and covering all
15possible inputs) in order to keep type checking decidable. The compile-time
16evaluator is part of the Idris kernel, and is implemented in Haskell using a
17HOAS (higher order abstract syntax) style representation of values. Since
18everything is known to have a normal form here, the evaluation strategy doesn't
19actually matter because either way it will get the same answer, and in practice
20it will do whatever the Haskell run-time system chooses to do.
22The REPL, for convenience, uses the compile-time notion of evaluation. As well
23as being easier to implement (because we have the evaluator available) this can
24be very useful to show how terms evaluate in the type checker. So you can see
25the difference between:
29 Idris> \n, m => (S n) + m
30 \n => \m => S (plus n m) : Nat -> Nat -> Nat
32 Idris> \n, m => n + (S m)
33 \n => \m => plus n (S m) : Nat -> Nat -> Nat
38Idris supports initialisation scripts.
43When the Idris REPL starts up, it will attempt to open the file
44repl/init in Idris's application data directory. The application data
45directory is the result of the Haskell function call
46``getAppUserDataDirectory "idris"``, which on most Unix-like systems
47will return $HOME/.idris and on various versions of Windows will return
48paths such as ``C:/Documents And Settings/user/Application Data/appName``.
50The file repl/init is a newline-separate list of REPL commands. Not all
51commands are supported in initialisation scripts — only the subset that
52will not interfere with the normal operation of the REPL. In particular,
53setting colours, display options such as showing implicits, and log
56Example initialisation script
57~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
60 :colour prompt white italic bold
61 :colour implicit magenta italic
68The current set of supported commands are:
70+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
71|Command | Arguments | Purpose |
72+================+==============================+==========================================================================================================+
73|<expr> | | Evaluate an expression |
74+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
75|:t :type | <expr> | Check the type of an expression |
76+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
77|:core | <expr> | View the core language representation of a term |
78+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
79|:miss :missing | <name> | Show missing clauses |
80+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
81|:doc | <name> | Show internal documentation |
82+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
83|:mkdoc | <namespace> | Generate IdrisDoc for namespace(s) and dependencies |
84+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
85|:apropos | [<package list>] <name> | Search names, types, and documentation |
86+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
87|:s :search | [<package list>] <expr> | Search for values by type |
88+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
89|:wc :whocalls | <name> | List the callers of some name |
90+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
91|:cw :callswho | <name> | List the callees of some name |
92+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
93|:browse | <namespace> | List the contents of some namespace |
94+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
95|:total | <name> | Check the totality of a name |
96+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
97|:r :reload | | Reload current file |
98+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
99|:l :load | <filename> | Load a new file |
100+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
101|:cd | <filename> | Change working directory |
102+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
103|:module | <module> | Import an extra module |
104+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
105|:e :edit | | Edit current file using $EDITOR or $VISUAL |
106+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
107|:m :metavars | | Show remaining proof obligations (holes) |
108+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
109|:p :prove | <hole> | Prove a hole |
110+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
111|:a :addproof | <name> | Add proof to source file |
112+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
113|:rmproof | <name> | Remove proof from proof stack |
114+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
115|:showproof | <name> | Show proof |
116+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
117|:proofs | | Show available proofs |
118+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
119|:x | <expr> | Execute IO actions resulting from an expression using the interpreter |
120+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
121|:c :compile | <filename> | Compile to an executable [codegen] <filename> |
122+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
123|:exec :execute | [<expr>] | Compile to an executable and run |
124+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
125|:dynamic | <filename> | Dynamically load a C library (similar to %dynamic) |
126+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
127|:dynamic | | List dynamically loaded C libraries |
128+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
129|:? :h :help | | Display this help text |
130+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
131|:set | <option> | Set an option (errorcontext, showimplicits, originalerrors, autosolve, nobanner, warnreach, evaltypes, |
133+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
134|:unset | <option> | Unset an option |
135+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
136|:color :colour | <option> | Turn REPL colours on or off; set a specific colour |
137+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
138|:consolewidth | auto|infinite|<number> | Set the width of the console |
139+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
140|:printerdepth | <number-or-blank> | Set the maximum pretty-printing depth, or infinite if nothing specified |
141+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
142|:q :quit | | Exit the Idris system |
143+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
144|:w :warranty | | Displays warranty information |
145+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
146|:let | (<top-level-declaration>)... | Evaluate a declaration, such as a function definition, instance implementation, or fixity declaration |
147+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
148|:unlet :undefine|(<name>)... | Remove the listed repl definitions, or all repl definitions if no names given |
149+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
150|:printdef | <name> | Show the definition of a function |
151+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
152|:pp :pprint | <option> <number> <name> | Pretty prints an Idris function in either LaTeX or HTML and for a specified width. |
153+----------------+------------------------------+----------------------------------------------------------------------------------------------------------+
163The command ``:help`` (or ``:h`` or ``:?``) prints a short summary of
164the available commands.
169If you would like to leave Idris, simply use ``:q`` or ``:quit``.
171Evaluating expressions
172~~~~~~~~~~~~~~~~~~~~~~
174To evaluate an expression, simply type it. If Idris is unable to infer
175the type, it can be helpful to use the operator ``the`` to manually
176provide one, as Idris's syntax does not allow for direct type
177annotations. Examples of ``the`` include:
185 Idris> the (List Nat) [1,2]
187 Idris> the (Vect _ Nat) [1,2]
190This may not work in cases where the expression still involves ambiguous
191names. The name can be disambiguated by using the ``with`` keyword:
196 When elaborating an application of function Prelude.Foldable.sum:
197 Can't disambiguate name: Prelude.List.::,
200 Idris> with List sum [1,2,3]
206To add a let binding to the REPL, use ``:let``. It's likely you'll also
207need to provide a type annotation. ``:let`` also works for other
208declarations as well, such as ``data``.
212 Idris> :let x : String; x = "hello"
218 Idris> :let data Foo : Type where Bar : Foo
222Getting type information
223~~~~~~~~~~~~~~~~~~~~~~~~
225To ask Idris for the type of some expression, use the ``:t`` command.
226Additionally, if used with an overloaded name, Idris will provide all
227overloadings and their types. To ask for the type of an infix operator,
228surround it in parentheses.
235 Prelude.Nat.plus : Nat -> Nat -> Nat
237 Builtins.++ : String -> String -> String
238 Prelude.List.++ : (List a) -> (List a) -> List a
239 Prelude.Vect.++ : (Vect m a) -> (Vect n a) -> Vect (m + n) a
241 plus (Builtins.fromInteger 4) : Nat -> Nat
243You can also ask for basic information about interfaces with ``:doc``:
254 (>>=) : Monad m => m a -> (a -> m b) -> m b
266Other documentation is also available from ``:doc``:
271 Prelude.Interfaces.(+) : Num ty => ty -> ty -> ty
275 The function is Total
280 Data type Prelude.Vect.Vect : Nat -> Type -> Type
288 Prelude.Vect.Nil : (a : Type) -> Vect 0 a
291 Prelude.Vect.:: : (a : Type) -> (n : Nat) -> a -> (Vect n a) -> Vect (S n) a
308 (>>=) : Monad m => m a -> (a -> m b) -> m b
312 The function is Total
313 join : Monad m => m (m a) -> m a
314 Also called flatten or mu
316 The function is Total
330The command ``:apropos`` searches names, types, and documentation for
331some string, and prints the results. For example:
336 eqPtr : Ptr -> Ptr -> IO Bool
339 eqSucc : (left : Nat) -> (right : Nat) -> (left = right) -> S left = S right
342 lemma_both_neq : ((x = x') -> _|_) -> ((y = y') -> _|_) -> ((x, y) = (x', y')) -> _|_
345 lemma_fst_neq_snd_eq : ((x = x') -> _|_) -> (y = y') -> ((x, y) = (x', y)) -> _|_
348 lemma_snd_neq : (x = x) -> ((y = y') -> _|_) -> ((x, y) = (x, y')) -> _|_
351 lemma_x_eq_xs_neq : (x = y) -> ((xs = ys) -> _|_) -> (x :: xs = y :: ys) -> _|_
354 lemma_x_neq_xs_eq : ((x = y) -> _|_) -> (xs = ys) -> (x :: xs = y :: ys) -> _|_
357 lemma_x_neq_xs_neq : ((x = y) -> _|_) -> ((xs = ys) -> _|_) -> (x :: xs = y :: ys) -> _|_
360 prim__eqB16 : Bits16 -> Bits16 -> Int
362 prim__eqB16x8 : Bits16x8 -> Bits16x8 -> Bits16x8
364 prim__eqB32 : Bits32 -> Bits32 -> Int
366 prim__eqB32x4 : Bits32x4 -> Bits32x4 -> Bits32x4
368 prim__eqB64 : Bits64 -> Bits64 -> Int
370 prim__eqB64x2 : Bits64x2 -> Bits64x2 -> Bits64x2
372 prim__eqB8 : Bits8 -> Bits8 -> Int
374 prim__eqB8x16 : Bits8x16 -> Bits8x16 -> Bits8x16
376 prim__eqBigInt : Integer -> Integer -> Int
378 prim__eqChar : Char -> Char -> Int
380 prim__eqFloat : Double -> Double -> Int
382 prim__eqInt : Int -> Int -> Int
384 prim__eqString : String -> String -> Int
386 prim__syntactic_eq : (a : Type) -> (b : Type) -> (x : a) -> (y : b) -> Maybe (x = y)
388 sequence : Traversable t => Applicative f => (t (f a)) -> f (t a)
391 sequence_ : Foldable t => Applicative f => (t (f a)) -> f ()
395 The Eq interface defines inequality and equality.
397 GTE : Nat -> Nat -> Type
398 Greater than or equal to
400 LTE : Nat -> Nat -> Type
401 Proofs that n is less than or equal to m
403 gte : Nat -> Nat -> Bool
404 Boolean test than one Nat is greater than or equal to another
406 lte : Nat -> Nat -> Bool
407 Boolean test than one Nat is less than or equal to another
410 Convert the number to its ASCII equivalent.
412 replace : (x = y) -> (P x) -> P y
413 Perform substitution in a term according to some equality.
415 sym : (l = r) -> r = l
416 Symmetry of propositional equality
418 trans : (a = b) -> (b = c) -> a = c
419 Transitivity of propositional equality
421``:search`` does a type-based search, in the spirit of Hoogle. See `Type-directed search (:search) <https://github.com/idris-lang/Idris-dev/wiki/Type-directed-search-%28%3Asearch%29>`_ for more details. Here is an example:
425 Idris> :search a -> b -> a
426 = Prelude.Basics.const : a -> b -> a
427 Constant function. Ignores its second argument.
429 = assert_smaller : a -> b -> b
430 Assert to the totality checker than y is always structurally
431 smaller than x (which is typically a pattern argument)
433 > malloc : Int -> a -> a
436 > Prelude.pow : Num a => a -> Nat -> a
439 > Prelude.Interfaces.(*) : Num a => a -> a -> a
442 > Prelude.Interfaces.(+) : Num a => a -> a -> a
445``:search`` can also look for dependent types:
449 Idris> :search plus (S n) n = plus n (S n)
450 < Prelude.Nat.plusSuccRightSucc : (left : Nat) ->
452 S (left + right) = left + S right
454Loading and reloading Idris code
455~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
457The command ``:l File.idr`` will load File.idr into the
458currently-running REPL, and ``:r`` will reload the last file that was
464All Idris definitions are checked for totality. The command
465``:total <NAME>`` will display the result of that check. If a definition
466is not total, this may be due to an incomplete pattern match. If that is
467the case, ``:missing`` or ``:miss`` will display the missing cases.
472The command ``:e`` launches your default editor on the current module.
473After control returns to Idris, the file is reloaded.
478The current module can be compiled to an executable using the command
479``:c <FILENAME>`` or ``:compile <FILENAME>``. This command allows to
480specify codegen, so for example JavaScript can be generated using
481``:c javascript <FILENAME>``. The ``:exec`` command will compile the
482program to a temporary file and run the resulting executable.
487Unlike GHCI, the Idris REPL is not inside of an implicit IO monad. This
488means that a special command must be used to execute IO actions.
489``:x tm`` will execute the IO action ``tm`` in an Idris interpreter.
491Dynamically loading C libraries
492~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
494Sometimes, an Idris program will depend on external libraries written in
495C. In order to use these libraries from the Idris interpreter, they must
496first be dynamically loaded. This is achieved through the
497``%dynamic <LIB>`` directive in Idris source files or through the
498``:dynamic <LIB>`` command at the REPL. The current set of dynamically
499loaded libraries can be viewed by executing ``:dynamic`` with no
500arguments. These libraries are available through the Idris FFI in `type
501providers <#type-providers>`__ and ``:exec``.
506Idris terms are available in amazing colour! By default, the Idris REPL
507uses colour to distinguish between data constructors, types or type
508constructors, operators, bound variables, and implicit arguments. This
509feature is available on all POSIX-like systems, and there are plans to
510allow it to work on Windows as well.
512If you do not like the default colours, they can be turned off using the
519and, when boredom strikes, they can be re-enabled using the command
525To modify a colour, use the command
529 :colour <CATEGORY> <OPTIONS>
531where ``<CATEGORY`` is one of ``keyword``, ``boundvar``, ``implicit``,
532``function``, ``type``, ``data``, or ``prompt``, and is a
533space-separated list drawn from the colours and the font options. The
534available colours are ``default``, ``black``, ``yellow``, ``cyan``,
535``red``, ``blue``, ``white``, ``green``, and ``magenta``. If more than
536one colour is specified, the last one takes precedence. The available
537options are ``dull`` and ``vivid``, ``bold`` and ``nobold``, ``italic``
538and ``noitalic``, ``underline`` and ``nounderline``, forming pairs of
539opposites. The colour ``default`` refers to your terminal's default
542The colours used at startup can be changed using REPL initialisation
545Colour can be disabled at startup by the ``--nocolour`` command-line
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