PureScript Documentation
Release 0.5.0
Phil Freeman
November 05, 2014
Contents
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3
3
4
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5
Getting Started
2.1 Compiler Installation . . . . . . .
2.2 Creating a new PureScript project
2.3 Compiler usage . . . . . . . . . .
2.4 psc-make . . . . . . . . . . . . .
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7
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8
Types
3.1 Primitive Types . . .
3.2 Arrays . . . . . . .
3.3 Records . . . . . . .
3.4 Tagged Unions . . .
3.5 Newtypes . . . . . .
3.6 Functions . . . . . .
3.7 Polymorphic Types .
3.8 Row Polymorphism
3.9 Rank N Types . . .
3.10 Rows . . . . . . . .
3.11 Type Synonyms . .
3.12 Constrained Types .
3.13 Type Annotations . .
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9
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4
Kind System
4.1 Row Kinds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 Quantification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5
Syntax
5.1 Whitespace Rules
5.2 Operators . . . . .
5.3 Literal Values . . .
5.4 Array Literals . . .
5.5 Record Literals . .
5.6 Array Indexing . .
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2
3
Introduction
1.1 Motivation . . . .
1.2 Hello, PureScript!
1.3 Another Example .
1.4 Related Projects .
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5.7
5.8
5.9
5.10
5.11
5.12
5.13
5.14
Property Accessors . . . .
Functions . . . . . . . . .
If-Then-Else Expressions
Do Notation . . . . . . .
Operators . . . . . . . . .
Record Updates . . . . .
Let Bindings . . . . . . .
Comments . . . . . . . .
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6
Type Classes
6.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 Superclasses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.3 Type Annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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7
Pattern Matching
7.1 Wildcard Patterns . .
7.2 Literal Patterns . . .
7.3 Variable Patterns . .
7.4 Array Patterns . . .
7.5 Cons Patterns . . . .
7.6 Constructor patterns
7.7 Record Patterns . . .
7.8 Nested Patterns . . .
7.9 Named Patterns . . .
7.10 Guards . . . . . . .
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8
Modules
8.1 Importing Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.2 Qualified Imports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8.3 Module Exports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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9
Foreign Function Interface
9.1 Importing Values . . . . . . . .
9.2 Inline Javascript . . . . . . . .
9.3 Importing Types . . . . . . . .
9.4 Importing Type Class Instances
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29
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10 Module Documentation
10.1 Module Prelude . . . . . . . . . .
10.2 Module Data.Function . . . . . . .
10.3 Module Data.Eq . . . . . . . . . .
10.4 Module Prelude.Unsafe . . . . . .
10.5 Module Control.Monad.Eff . . . .
10.6 Module Control.Monad.Eff.Unsafe
10.7 Module Debug.Trace . . . . . . . .
10.8 Module Control.Monad.ST . . . .
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Contents:
Contents
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2
Contents
CHAPTER 1
Introduction
PureScript is a small strongly, statically typed compile-to-JS language with a number of interesting features, such as:
• Type Inference
• Higher Kinded Polymorphism
• Support for basic Javascript types
• Extensible records
• Extensible effects
• Optimizer rules for generation of efficient Javascript
• Pattern matching
• Simple FFI
• Modules
• Rank N Types
• Do Notation
• Tail-call elimination
• Type Classes
1.1 Motivation
I was looking for a simple functional language which would compile to JavaScript and have the following characteristics:
• Generate simple readable Javascript
• Provide the ability to compile to tight loops if necessary
• Reasonable type system
• Ideally, written in a programming language I would enjoy working in
• Provides a simple interface to existing Javascript code
I didn’t find exactly what I was looking for, so I wrote PureScript. It doesn’t have everything right now, but it should
serve as a simple core on which to develop new ideas.
PureScript was originally designed to implement purely functional core logic. However, recent additions to the compiler and libraries now also make it a good option for general-purpose programming.
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PureScript can also be seen as a trade-off between a theoretically ideal language and one which generates reasonably
high performance code.
1.2 Hello, PureScript!
As an introductory example, here is the usual “Hello World” written in PureScript:
module Main where
import Debug.Trace
main = trace "Hello, World!"
which compiles to the following Javascript, ignoring the Prelude:
var Main;
(function (Main) {
var main = trace("Hello, World!");
Main.main = main;
})(Main = Main || {});
The following command will compile and execute the PureScript code above:
psc input.purs --main | node
1.3 Another Example
The following code defines a Person data type and a function to generate a string representation for a Person:
data Person = Person { name :: String, age :: Number }
showPerson :: Person -> String
showPerson (Person o) = o.name ++ ", aged " ++ show o.age
examplePerson :: Person
examplePerson = Person { name: "Bonnie", age: 26 }
Line by line, this reads as follows:
• Person is a data type with one constructor, also called Person
• The Person constructor takes an object with two properties, name which is a String, and age which is a
Number
• The showPerson function takes a Person and returns a String
• showPerson works by case analysis on its argument, first matching the constructor Person and then using
string concatenation and object accessors to return its result.
• examplePerson is a Person object, made with the Person constructor and given the String “Bonnie” for
the name value and the Number 26 for the age value.
The generated Javascript looks like this:
var Person = function (value) {
return { ctor: ’Person’, values: [value] };
};
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function showPerson(_1) {
return _1.values[0].name + ", aged " + numberToString(_1.values[0].age);
};
var examplePerson = Person({
name: "Bonnie",
age: 26
});
1.4 Related Projects
PureScript might be compared to other AltJS projects such as Roy, Haste, Fay, Elm and GHCJS. Certainly, there is a
lot of overlap in terms of syntax, but the goals of PureScript listed above separate it in one or more ways from each of
these languages.
Roy is probably the most similar language on the list, and was a large influence on the development of PureScript.
There are however, key differences in the foreign function interface, the type system and the choice of development
language (Haskell vs. Javascript)
Projects such as Haste, Fay and GHCJS aim to use some combination of the GHC compiler itself and/or its intermediate
representation, Core, to perform some of the tasks involved in compilation such as parsing and type checking. This
usually gives the advantage that tools and libraries can be shared with Haskell, but often at the cost of the size of the
generated Javascript. This is the main practical difference between PureScript and these projects.
Elm also shares a lot in terms of functionality with PureScript. Elm is designed for functional reactive programming,
and focusses on tools and language features suitable for that domain, while PureScript focusses on the development
of purely functional core application logic. Another difference between PureScript and Elm is PureScript’s lack of a
runtime system.
1.4. Related Projects
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Chapter 1. Introduction
CHAPTER 2
Getting Started
2.1 Compiler Installation
If you have the Haskell Plaform installed, then you can install the latest released version from Hackage:
cabal update
cabal install purescript
If you would like to build the latest version of the code, clone this repository and build:
git clone [email protected]:purescript/purescript.git
cd purescript
cabal configure --enable-tests
cabal build
cabal test
cabal install
Alternatively, consider installing PureScript in a Cabal sandbox using cabal sandbox init.
2.2 Creating a new PureScript project
You can create a new PureScript project using grunt-init and this PureScript project template. This will give you
a project that uses Grunt as its build tool and Bower for dependency management. See the README for step-by-step
instructions.
2.3 Compiler usage
The psc executable takes a list of PureScript source files as arguments and by default writes out its errors or output to
the console.
The following options are supported:
--stdin
Read input from standard input instead of from files.
--output
Write the generated Javascript to the specified file.
--externs
Write a list of foreign imports declarations to the specified file in addition to
generating Javascript output.
--no-tco
Turn off tail-call elimination.
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--no-prelude
Do not include the Prelude in the generated Javascript.
--no-magic-do
Turn off optimizations which inline calls to >>= for the Eff monad.
--no-opts
Disable all optimizations.
--main
Generate a call to main in the specified module after all other generated
Javascript. Defaults to Main if the option is used but no value is provided.
--module
If specified, any code which is not referenced transitively from this module will
be removed. This argument can be used multiple times.
--codegen
A list of modules for which Javascript and externs should be generated. This
argument can be used multiple times.
--browser-namespace Specify the namespace that PureScript modules will be exported to when running in the browser.
--verbose-errors
Generate verbose error messages.
2.4 psc-make
The psc-make executable makes CommonJS modules and supports incremental compilation. Unlike psc, it does
not do dead code elimination.
The following command line options are supported:
8
--output=VAL
The output directory. Default: output.
--verbose-errors
Display verbose error messages.
--help=FMT
Show this help in format FMT (pager, plain, or groff). Default: pager.
--no-magic-do
Disable the optimization that overloads the do keyword to generate efficient code
specifically for the Eff monad.
--no-opts
Skip the optimization phase.
--no-prelude
Omit the Prelude.
--no-tco
Disable tail call optimizations
Chapter 2. Getting Started
CHAPTER 3
Types
The type system defines the following types:
• Primitive Types: Number, String, Boolean
• Arrays
• Records
• Tagged Unions
• Newtypes
• Functions
• Polymorphic Types
• Constrained Types
• Type Synonyms
• Rows
3.1 Primitive Types
The three primitive types String, Number and Boolean correspond to their Javascript equivalents at runtime.
3.2 Arrays
PureScript arrays correspond to Javascript arrays at runtime, but all elements in an array must have the same type.
3.3 Records
PureScript records correspond to Javascript objects. They may have zero or more named fields, each with their own
types.
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3.4 Tagged Unions
Tagged unions consist of one or more constructors, each of which takes zero or more arguments.
Tagged unions can only be created using their constructors, and deconstructed through pattern matching (see later).
For example:
data Foo = Foo | Bar String
runFoo Foo = "It’s a Foo"
runFoo (Bar s) = "It’s a Bar. The string is " ++ s
test = runFoo Foo ++ runFoo (Bar "Test")
In the example, Foo is a tagged union type which has two constructors. Its first constructor Foo takes no arguments,
and its second Bar takes one, which must be a String.
runFoo is an example of pattern matching on a tagged union type to discover its constructor, and the last line shows
how to construct values of type Foo.
3.5 Newtypes
Newtypes are like data types introduced with the data keyword, but are restricted to a single contructor which
contains a single argument. Newtypes are introduced with the newtype keyword:
newtype Percentage = Percentage Number
The representation of a newtype at runtime is the same as the underlying data type. For example, a value of type
Percentage is just a JavaScript number at runtime.
Newtypes can be assigned their own type class instances, so for example, Percentage can be given its own Show
instance:
instance showPercentage :: Show Percentage where
show (Percentage n) = show n ++ "%"
3.6 Functions
Functions in PureScript are like their Javascript counterparts, but always have exactly one argument.
3.7 Polymorphic Types
Expressions defined at the top level may have polymorphic types.
Here is an example:
identity x = x
identity is inferred to have (polymorphic) type forall t0. t0 -> t0. This means that for any type t0,
identity can be given a value of type t0 and will give back a value of the same type.
A type annotation can also be provided:
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identity :: forall a. a -> a
identity x = x
3.8 Row Polymorphism
Polymorphism is not limited to abstracting over types. Values may also be polymorphic in types with other kinds, such
as rows or effects (see “Kind System”).
For example, the following function accesses two properties on a record:
addProps o = o.foo + o.bar
The inferred type of addProps is:
forall r. { foo :: Number, bar :: Number | r } -> Number
Here, the type variable r has kind # * - it represents a row of types. It can be instantiated with any row of named
types.
In other words, addProps accepts any record which has properties foo and bar, and any other record properties.
Therefore, the following application compiles:
addProps { foo: 1, bar: 2, baz: 3 }
even though the type of addProps does not mention the property baz. However, the following does not compile:
addProps { foo: 1 }
since the bar property is missing.
3.9 Rank N Types
It is also possible for the forall quantifier to appear on the left of a function arrow, inside types record fields and
data constructors, and in type synonyms.
In most cases, a type annotation is necessary when using this feature.
As an example, we can pass a polymorphic function as an argument to another function:
poly :: (forall a. a -> a) -> Boolean
poly f = (f 0 < 1) == f true
Notice that the polymorphic function’s type argument is instantiated to both Number and Boolean.
An argument to poly must indeed be polymorphic. For example, the following fails:
test = poly (\n -> n + 1)
since the skolemized type variable a does not unify with Number.
3.10 Rows
A row of types represents an unordered collection of named types without duplicates.
3.8. Row Polymorphism
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Rows have kind # k for some kind k, and so values do not have types which are rows. Rather, rows can be used in
type signatures to define record types or other type where labelled, unordered types are useful.
To denote a closed row, separate the fields with commas, with each label separated from its type with a double colon:
(name :: String, age :: Number)
It may be necessary, depending on the context, to surround a row in parentheses.
To denote an open row (i.e. one which may unify with another row to add new fields), separate the specified terms
from a row variable by a pipe:
(name :: String, age :: Number | r)
3.11 Type Synonyms
For convenience, it is possible to declare a synonym for a type using the type keyword. Type synonyms can include
type arguments.
For example:
type Foo = { foo :: Number, bar :: Number }
addFoo :: Foo -> Number
addFoo = \o -> o.foo + o.bar
3.12 Constrained Types
Polymorphic types may be predicated on one or more constraints. See the chapter on type classes for more
information.
3.13 Type Annotations
Most types can be inferred (not including Rank N Types and constrained types), but annotations can optionally be
provided using a double-colon:
one = 1 :: Number
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Chapter 3. Types
CHAPTER 4
Kind System
The kind system defines the following kinds:
• *, the kind of types.
• !, the kind of effects.
• Arrow kinds k1 -> k2
• Row kinds # k
4.1 Row Kinds
The kind # k of rows is used to classify labelled, unordered collections of types of kind k.
For example # * is the kind of rows of types, as used to define records, and # ! is the kind of rows of effects, used
to define the monad Eff of extensible effects.
4.2 Quantification
A type variable can refer to not only a type or a row, but a type constructor, or row constructor etc., and type variables
with those kinds can be bound inside a forall quantifier.
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Chapter 4. Kind System
CHAPTER 5
Syntax
5.1 Whitespace Rules
Syntax is whitespace sensitive. The general rule of thumb is that declarations which span multiple lines should be
indented past the column on which they were first defined on their subsequent lines.
That is, the following is valid:
foo = bar(x) +
baz(x)
But this is not:
foo = bar(x) +
baz(x)
5.2 Operators
Binary operators in PureScript are just regular functions. The Prelude defines a number of operators which correspond
to Javascript’s operators.
The Prelude defines the following functions which correspond to Javascript’s unary operators:
Function
negate
not
complement
Operator
!
~
Meaning
Numeric negation
Boolean negation
Binary negation
and the following binary operators:
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Function
+
*
/
%
==
/=
<
<=
>
>=
&&
||
&
|
^
shl
shr
zshr
++
JS Operator
+
*
/
%
==
!=
<
<=
>
>=
&&
||
&
|
^
<<
>>
>>>
+
Meaning
Numeric addition
Numeric subtraction
Numeric multiplication
Numeric division
Numeric modulus
Equality check
Inequality check
Less than
Less than or equal
Greater than
Greater than or equal
Boolean AND
Boolean OR
Binary AND
Binary OR
Binary XOR
Shift Left
Shift Right
Zero-Fill Shift Right
String concatenation
5.3 Literal Values
Numeric literals can be integers or floating point numbers. Numbers in hexadecimal notation should be preceded by
the characters 0x:
16
16.0
0xF0
String literals are enclosed in double-quotes and may extend over multiple lines. Line breaks should be surrounded by
slashes as follows:
"Hello World"
"Hello \
\World"
The two boolean literals are true and false.
5.4 Array Literals
Array literals are surrounded by square brackets, as in Javascript:
[]
[1, 2, 3]
5.5 Record Literals
Record literals are surrounded by braces, as in Javascript:
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{}
{ foo: "Foo", bar: 1 }
5.6 Array Indexing
The Prelude.Unsafe module defines the unsafeIndex function which retrieves the element of an array at an
index:
unsafeIndex :: forall a. [a] -> Number -> a
The code generator will turn the expression unsafeIndex arr index into the simplified Javascript
arr[index].
The purescript-array core library defines an alternative safe version !! of unsafeIndex which checks
arrays bounds and returns a value of type Maybe a.
5.7 Property Accessors
To access a property of a record, use a dot, followed by the property name, as in Javascript:
rec.propertyName
5.8 Functions
Functions are introduced by using a backslash followed by a list of argument names:
example1 = \a b -> a + b
which would correspond to the following Javascript:
function example1(a) {
return function (b) {
return a + b;
}
}
Function application is indicated by just the juxtaposition of a function with its arguments:
example1 10 20
Functions can also be defined at the top level by providing a list of patterns and an optional guard on the left hand side
of the equals sign:
f [] [] = []
f (x:xs) (y:ys) = x + y : f xs ys
5.9 If-Then-Else Expressions
The if, then and else keywords can be used to create conditional expressions. In this case, the else block is
always required.
5.6. Array Indexing
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For example:
conditional = if 2 > 1 then "ok" else "oops"
5.10 Do Notation
The do keyword introduces simple syntactic sugar for monadic expressions.
Here is an example, using the maybe monad:
data Maybe a = Nothing | Just a
isEven :: Number -> Maybe Unit
isEven n | n % 2 == 0 = Just unit
isEven _ = Nothing
evenSum a b = do
n <- a
m <- b
let sum = n + m
isEven sum
return sum
isEven adds two values of type Maybe Number and returns their sum, if the sum is even. If the sum is odd,
evenSum returns Nothing.
When using do notation, the corresponding type constructor must be an instance of the Prelude.Monad type class.
Statements can have the following form:
• a <- x which desugars to x >>= \a -> ...
• x which desugars to x >>= \_ -> ... or just x if this is the last statement.
• A let binding let a = x where a can be either a name or a binder. Note the lack of the in keyword.
The example evenSum desugars to:
evenSum a b =
a >>= \n ->
b >>= \m ->
let sum = n + m in
isEven sum >>= \_ ->
return sum
Binders can be used on the left hand side of <- or =. For example:
test arr = do
(x:y:_) <- arr
ret (x + y)
A pattern match failure will generate a runtime exception, just as in the case of a regular case statement.
5.11 Operators
User-defined infix operators can be created by enclosing names in parentheses.
E.g. to create an infix synonym for the Data.Array.range function:
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(..) :: Number -> Number -> [Number]
(..) = Data.Array.range
This function can be used as follows:
oneToTen = 1 .. 10
Regular functions can be used as operators by enclosing their names in backticks:
foo x y = x * y + y
test = 10 ‘foo‘ 20
Fixity declarations can associate a precedence level, which is a natural number, to a user-defined operator, and specify
which way it associates:
infix 5 ..
infixl 7 %%
infixr 9 ^^
5.12 Record Updates
Properties on records can be updated using the following syntax:
o { key = value, ..., key = value }
For example, the following function increments the foo property on its argument:
incr o = o { foo = o.foo + 1 }
5.13 Let Bindings
The let keywords a collection of local declarations, which may be mutually recursive, and which may include type
declarations:
factorial :: Number -> Number
factorial =
let
go :: Number -> Number -> Number
go acc 1 = acc
go acc n = go (acc * n) (n - 1)
in
go 1
The where keyword can also be used to introduce local declarations at the end of a value declaration:
factorial :: Number -> Number
factorial = go 1
where
go :: Number -> Number -> Number
go acc 1 = acc
go acc n = go (acc * n) (n - 1)
5.12. Record Updates
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5.14 Comments
A single line comment starts with --:
-- This is a comment
Multi-line comments are enclosed in {- and -}. These can be nested:
{- Comment {- nested comment -} continued comment -}
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Chapter 5. Syntax
CHAPTER 6
Type Classes
PureScript has basic support for type classes via the class and instance keywords.
Types appearing in class instances are must be of the form String, Number, Boolean, or C t1 ...
C is a type constructor (including [] and -> and t_i are types of the same form).
tn where
Type class instances are resolved based on the order in which they appeared in the source files. Overlapping instances
will result in a compilation error.
6.1 Example
Here is an example of the Show typeclass, with instances for String, Booleans and []:
class Show a where
show :: a -> String
instance showString :: Show String where
show s = s
instance showBoolean :: Show Boolean where
show true = "true"
show false = "false"
instance showArray :: (Show a) => Show [a] where
show [] = "[]"
show (x:xs) = show x ++ " : " ++ showArray xs
example = show [true, false]
6.2 Superclasses
Superclass implications can be indicated in a class declaration with a backwards fat arrow <=:
class (Monad m) <= MonadFail m where
fail :: forall a. String -> m a
Superclass instances will be used when searching for an instance of a subclass. For example, in the code below, the
Monad constraint introduced by the return function can be discharged since Monad is a superclass of MonadFail:
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assert :: forall m. (MonadFail m) => Boolean -> m Unit
assert true = return unit
assert false = fail "Assertion failed"
6.3 Type Annotations
A constrained type will never be inferred for a top-level declaration without an explicit type signature.
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Chapter 6. Type Classes
CHAPTER 7
Pattern Matching
Pattern matching deconstructs a value to bring zero or more expressions into scope. Pattern matches are introduced
with the case keyword.
Pattern matches have the following general form:
case value of
pattern -> result
...
pattern -> result
Pattern matching can also be used in the declaration of functions, as we have already seen:
fn pattern_1 ... pattern_n = result
Patterns can also be used when introducing functions. For example:
example x y z = x * y + z
The following pattern types are supported:
• Wildcard pattern
• Literal patterns
• Variable pattern
• Array patterns
• Cons patterns
• Constructor patterns
• Record patterns
• Named patterns
• Guards
Patterns need not be exhaustive. A pattern match failed exception will be thrown at runtime if no pattern matches the
input.
7.1 Wildcard Patterns
The wilcard _ matches any input and brings nothing into scope:
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f _ = 0
7.2 Literal Patterns
Literal patterns are provided to match on primitives:
f true = 0
f false = 1
g "Foo" = 0
g _ = 1
h 0 = 0
h _ = 1
7.3 Variable Patterns
A variable pattern matches any input and binds that input to its name:
double x = x * 2
7.4 Array Patterns
Array patterns match an input which is an array, and bring its elements into scope. For example:
f [x] = x
f [x, y] = x * y
f _ = 0
Here, the first pattern only matches arrays of length one, and brings the first element of the array into scope.
The second pattern matches arrays with two elements, and brings the first and second elements into scope.
7.5 Cons Patterns
The head and tail of a non-empty array can be matched by using a cons pattern:
sum [] = 0
sum (x : xs) = x + sum xs
: associates to the right:
addPairs (x : y : xs) = x * y + addPairs xs
addPairs _ = 0
7.6 Constructor patterns
Constructor patterns match a data constructor and its arguments:
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data Foo = Foo String | Bar Number Boolean
foo (Foo s) = true
foo (Bar _ b) = b
7.7 Record Patterns
Record patterns match an input which is a record, and bring its properties into scope:
f { foo = "Foo", bar = n } = n
f _ = 0
7.8 Nested Patterns
The patterns above can be combined to create larger patterns. For example:
f { arr = x : _, take = "car" } = x
f { arr = _ : x : _, take = "cadr" } = x
f _ = 0
7.9 Named Patterns
Named patterns bring additional names into scope when using nested patterns. Any pattern can be named by using the
@ symbol:
f a@(_ : _ : _) = true
f _ = false
Here, in the first pattern, any array with two or more elements will be matched and bound to the variable a.
7.10 Guards
Guards are used to impose additional constraints inside a pattern using boolean-valued expressions, and are introduced
with a pipe after the pattern:
evens [] = 0
evens (x : xs) | x % 2 == 0 = 1 + evens xs
evens (_ : xs) = evens xs
When using patterns to define a function at the top level, guards appear after all patterns:
greater x y | x > y = true
greater _ _ = false
7.7. Record Patterns
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Chapter 7. Pattern Matching
CHAPTER 8
Modules
All code in PureScript is contained in a module. Modules are introduced using the module keyword:
module A where
id x = x
When referencing values or data types in another module, names may be qualified by using a dot:
module B where
foo = A.id
8.1 Importing Modules
A module can be imported using the import keyword. This will create aliases for all of the values and types in the
imported module:
module B where
import A
Alternatively, a list of names to import can be provided in parentheses:
module B where
import A (runFoo)
Values, type constructors and data constructors can all be explicitly imported. A type constructor should be followed
by a list of associated data constructors to import in parentheses. A double dot (..) can be used to import all data
constructors for a given type constructor:
module B where
import A (runFoo, Foo(..), Bar(Bar))
8.2 Qualified Imports
Modules can also be imported qualified, which means that their names will not be brought directly into scope, but
rather, aliased to a different module name. This can be helpful when avoiding naming conflicts:
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module Main where
import qualified Data.Array as A
null = ...
Here, the name null would ordinarily conflict with null from Data.Array, but the qualified import solves this
problem. Data.Array.null can be referenced using A.null instead.
8.3 Module Exports
Module exports can be restricted to a set of names by providing that set in parentheses in the module declaration:
module A (runFoo, Foo(..)) where
The types of names which can be exported is the same as for module imports.
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Chapter 8. Modules
CHAPTER 9
Foreign Function Interface
9.1 Importing Values
The foreign import keywords declare a value which is defined in Javascript, and its type:
foreign import pow :: Number -> Number -> Number
9.2 Inline Javascript
A foreign import declaration may optionally contain its definition in Javascript as a string literal. If this is provided,
the string will be inserted directly into the generated Javascript before the current module definition:
foreign import pow
"""function pow(n) {
return function(p) {
return Math.pow(n, p);
};
}""" :: Number -> Number -> Number
9.3 Importing Types
To declare a new type with no constructors, use foreign import data and provide the kind:
foreign import data DOM :: *
foreign import document :: {
createElement :: String -> DOM
}
9.4 Importing Type Class Instances
Type class instances can be imported with foreign import instance:
foreign import instance showString :: Prelude.Show String
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Chapter 9. Foreign Function Interface
CHAPTER 10
Module Documentation
10.1 Module Prelude
10.1.1 Types
data
LT
GT
EQ
Ordering where
:: Ordering
:: Ordering
:: Ordering
data Unit where
Unit :: { } -> Unit
10.1.2 Type Classes
Figure 10.1: Prelude
class Alternative f where
empty :: forall a. f a
(<|>) :: forall a. f a -> f a -> f a
class (Apply f) <= Applicative f where
pure :: forall a. a -> f a
class (Functor f) <= Apply f where
(<*>) :: forall a b. f (a -> b) -> f a -> f b
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class (Apply m) <= Bind m where
(>>=) :: forall a b. m a -> (a -> m b) -> m b
class Bits b where
(&) :: b -> b -> b
(|) :: b -> b -> b
(^) :: b -> b -> b
shl :: b -> Number -> b
shr :: b -> Number -> b
zshr :: b -> Number -> b
complement :: b -> b
class BoolLike b where
(&&) :: b -> b -> b
(||) :: b -> b -> b
not :: b -> b
class (Semigroupoid a) <= Category a where
id :: forall t. a t t
class Eq a where
(==) :: a -> a -> Boolean
(/=) :: a -> a -> Boolean
class Functor f where
(<$>) :: forall a b. (a -> b) -> f a -> f b
class (Applicative m, Bind m) <= Monad m where
class Num a where
(+) :: a -> a ->
(-) :: a -> a ->
(*) :: a -> a ->
(/) :: a -> a ->
(%) :: a -> a ->
negate :: a -> a
a
a
a
a
a
class (Eq a) <= Ord a where
compare :: a -> a -> Ordering
class Semigroup a where
(<>) :: a -> a -> a
class Semigroupoid a where
(<<<) :: forall b c d. a c d -> a b c -> a b d
class Show a where
show :: a -> String
10.1.3 Type Class Instances
instance applicativeArr :: Applicative (Prim.Function r)
instance applyArr :: Apply (Prim.Function r)
instance bindArr :: Bind (Prim.Function r)
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instance bitsNumber :: Bits Number
instance boolLikeBoolean :: BoolLike Boolean
instance categoryArr :: Category Prim.Function
instance eqArray :: (Eq a) => Eq [a]
instance eqBoolean :: Eq Boolean
instance eqNumber :: Eq Number
instance eqOrdering :: Eq Ordering
instance eqString :: Eq String
instance eqUnit :: Eq Unit
instance functorArr :: Functor (Prim.Function r)
instance monadArr :: Monad (Prim.Function r)
instance numNumber :: Num Number
instance ordArray :: (Ord a) => Ord [a]
instance ordBoolean :: Ord Boolean
instance ordNumber :: Ord Number
instance ordString :: Ord String
instance ordUnit :: Ord Unit
instance semigroupArr :: (Semigroup s’) => Semigroup (s -> s’)
instance semigroupString :: Semigroup String
instance semigroupUnit :: Semigroup Unit
instance semigroupoidArr :: Semigroupoid Prim.Function
instance showArray :: (Show a) => Show [a]
instance showBoolean :: Show Boolean
instance showNumber :: Show Number
instance showOrdering :: Show Ordering
instance showString :: Show String
instance showUnit :: Show Unit
10.1. Module Prelude
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10.1.4 Values
(#) :: forall a b. a -> (a -> b) -> b
($) :: forall a b. (a -> b) -> a -> b
(++) :: forall s. (Semigroup s) => s -> s -> s
(:) :: forall a. a -> [a] -> [a]
(<) :: forall a. (Ord a) => a -> a -> Boolean
(<=) :: forall a. (Ord a) => a -> a -> Boolean
(>) :: forall a. (Ord a) => a -> a -> Boolean
(>=) :: forall a. (Ord a) => a -> a -> Boolean
(>>>) :: forall a b c d. (Semigroupoid a) => a b c -> a c d -> a b d
ap :: forall m a b. (Monad m) => m (a -> b) -> m a -> m b
asTypeOf :: forall a. a -> a -> a
cons :: forall a. a -> [a] -> [a]
const :: forall a b. a -> b -> a
flip :: forall a b c. (a -> b -> c) -> b -> a -> c
liftA1 :: forall f a b. (Applicative f) => (a -> b) -> f a -> f b
liftM1 :: forall m a b. (Monad m) => (a -> b) -> m a -> m b
refEq :: forall a. a -> a -> Boolean
refIneq :: forall a. a -> a -> Boolean
return :: forall m a. (Monad m) => a -> m a
unit :: Unit
void :: forall f a. (Functor f) => f a -> f Unit
10.2 Module Data.Function
10.2.1 Types
data Fn0 :: * -> *
data Fn1 :: * -> * -> *
data Fn10 :: * -> * -> * -> * -> * -> * -> * -> * -> * -> * -> * -> *
data Fn2 :: * -> * -> * -> *
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data Fn3 :: * -> * -> * -> * -> *
data Fn4 :: * -> * -> * -> * -> * -> *
data Fn5 :: * -> * -> * -> * -> * -> * -> *
data Fn6 :: * -> * -> * -> * -> * -> * -> * -> *
data Fn7 :: * -> * -> * -> * -> * -> * -> * -> * -> *
data Fn8 :: * -> * -> * -> * -> * -> * -> * -> * -> * -> *
data Fn9 :: * -> * -> * -> * -> * -> * -> * -> * -> * -> * -> *
10.2.2 Values
mkFn0 :: forall a. (Unit -> a) -> Fn0 a
mkFn1 :: forall a b. (a -> b) -> Fn1 a b
mkFn10 :: forall a b c d e f g h i j k. (a -> b -> c -> d -> e -> f -> g -> h -> i -> j -> k) -> Fn10
mkFn2 :: forall a b c. (a -> b -> c) -> Fn2 a b c
mkFn3 :: forall a b c d. (a -> b -> c -> d) -> Fn3 a b c d
mkFn4 :: forall a b c d e. (a -> b -> c -> d -> e) -> Fn4 a b c d e
mkFn5 :: forall a b c d e f. (a -> b -> c -> d -> e -> f) -> Fn5 a b c d e f
mkFn6 :: forall a b c d e f g. (a -> b -> c -> d -> e -> f -> g) -> Fn6 a b c d e f g
mkFn7 :: forall a b c d e f g h. (a -> b -> c -> d -> e -> f -> g -> h) -> Fn7 a b c d e f g h
mkFn8 :: forall a b c d e f g h i. (a -> b -> c -> d -> e -> f -> g -> h -> i) -> Fn8 a b c d e f g h
mkFn9 :: forall a b c d e f g h i j. (a -> b -> c -> d -> e -> f -> g -> h -> i -> j) -> Fn9 a b c d
on :: forall a b c. (b -> b -> c) -> (a -> b) -> a -> a -> c
runFn0 :: forall a. Fn0 a -> a
runFn1 :: forall a b. Fn1 a b -> a -> b
runFn10 :: forall a b c d e f g h i j k. Fn10 a b c d e f g h i j k -> a -> b -> c -> d -> e -> f ->
runFn2 :: forall a b c. Fn2 a b c -> a -> b -> c
runFn3 :: forall a b c d. Fn3 a b c d -> a -> b -> c -> d
runFn4 :: forall a b c d e. Fn4 a b c d e -> a -> b -> c -> d -> e
runFn5 :: forall a b c d e f. Fn5 a b c d e f -> a -> b -> c -> d -> e -> f
runFn6 :: forall a b c d e f g. Fn6 a b c d e f g -> a -> b -> c -> d -> e -> f -> g
10.2. Module Data.Function
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runFn7 :: forall a b c d e f g h. Fn7 a b c d e f g h -> a -> b -> c -> d -> e -> f -> g -> h
runFn8 :: forall a b c d e f g h i. Fn8 a b c d e f g h i -> a -> b -> c -> d -> e -> f -> g -> h ->
runFn9 :: forall a b c d e f g h i j. Fn9 a b c d e f g h i j -> a -> b -> c -> d -> e -> f -> g -> h
10.3 Module Data.Eq
10.3.1 Types
data Ref a where
Ref :: a -> Ref a
10.3.2 Type Class Instances
instance eqRef :: Eq (Ref a)
instance functorRef :: Functor Ref
10.3.3 Values
liftRef :: forall a b. (a -> a -> b) -> Ref a -> Ref a -> b
10.4 Module Prelude.Unsafe
10.4.1 Values
unsafeIndex :: forall a. [a] -> Number -> a
10.5 Module Control.Monad.Eff
10.5.1 Types
data Eff :: # ! -> * -> *
type Pure a = forall e. Eff e a
10.5.2 Type Class Instances
instance applicativeEff :: Applicative (Eff e)
instance applyEff :: Apply (Eff e)
instance bindEff :: Bind (Eff e)
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instance functorEff :: Functor (Eff e)
instance monadEff :: Monad (Eff e)
10.5.3 Values
bindE :: forall e a b. Eff e a -> (a -> Eff e b) -> Eff e b
forE :: forall e. Number -> Number -> (Number -> Eff e Unit) -> Eff e Unit
foreachE :: forall e a. [a] -> (a -> Eff e Unit) -> Eff e Unit
returnE :: forall e a. a -> Eff e a
runPure :: forall a. Pure a -> a
untilE :: forall e. Eff e Boolean -> Eff e Unit
whileE :: forall e a. Eff e Boolean -> Eff e a -> Eff e Unit
10.6 Module Control.Monad.Eff.Unsafe
10.6.1 Values
unsafeInterleaveEff :: forall eff1 eff2 a. Eff eff1 a -> Eff eff2 a
10.7 Module Debug.Trace
10.7.1 Types
data Trace :: !
10.7.2 Values
print :: forall a r. (Show a) => a -> Eff (trace :: Trace | r) Unit
trace :: forall r. String -> Eff (trace :: Trace | r) Unit
10.8 Module Control.Monad.ST
10.8.1 Types
10.6. Module Control.Monad.Eff.Unsafe
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data ST :: * -> !
data STArray :: * -> * -> *
data STRef :: * -> * -> *
10.8.2 Values
modifySTRef :: forall a h r. STRef h a -> (a -> a) -> Eff (st :: ST h | r) a
newSTArray :: forall a h r. Number -> a -> Eff (st :: ST h | r) (STArray h a)
newSTRef :: forall a h r. a -> Eff (st :: ST h | r) (STRef h a)
peekSTArray :: forall a h r. STArray h a -> Number -> Eff (st :: ST h | r) a
pokeSTArray :: forall a h r. STArray h a -> Number -> a -> Eff (st :: ST h | r) a
readSTRef :: forall a h r. STRef h a -> Eff (st :: ST h | r) a
runST :: forall a r. (forall h. Eff (st :: ST h | r) a) -> Eff r a
runSTArray :: forall a r. (forall h. Eff (st :: ST h | r) (STArray h a)) -> Eff r [a]
writeSTRef :: forall a h r. STRef h a -> a -> Eff (st :: ST h | r) a
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CHAPTER 11
Indices and tables
• genindex
• modindex
• search
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