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PSCi "PureScript Interactive" is the REPL for PureScript. It is often a good way to explore your code, do some basic testing, or to get a feel for a new library.

Getting Started

Use Pulp to configure and start PSCi:

$ npm install -g pulp # Install pulp

$ cd my-project # Enter an empty folder

$ pulp init # Initialize a pulp environment

$ pulp psci # Fire up the interpreter psci

PSCi, version 0.9.1
Type :? for help

> "hello"
"hello"

> import Prelude

> 1 + 2 * 3
7

> import Control.Monad.Eff.Console

> log "print this to the screen"
print this to the screen
unit

For more information about getting started with a development environment, see this guide.

Basic usage

Type expressions into the REPL to have them evaluated:

> 3 + 4
7

Introduce bindings with =:

> x = 4
> x + 9
13

You can also define data types, type classes, and type class instances (you may need to use multi-line mode for this):

> data Season = Spring | Summer | Autumn | Winter
> class Shout a where shout :: a -> a
> instance shoutString :: Shout String where shout s = s <> "!"

Paste mode (previously --multi-line-mode)

Enter :paste (or :p) to enter multi-line (or "paste") mode. Terminate it with Control-D key.

> import Prelude
> :paste
… add :: Int -> Int -> Int
… add = \x y -> x + y
> add 10 20
> (^D)
30

Demo

purescript-psci-support

$ psci

PSCi requires the purescript-psci-support package to be installed.
You can install it using Bower as follows:

  bower i purescript-psci-support --save-dev

For help getting started, visit http://wiki.purescript.org/PSCi

The PureScript compiler suite (i.e. the executable purs), unlike most compilers, does not ship with a standard library. In PureScript, even Prelude is a normal module, just like any other. Consequentially, psci requires a specific library to be installed in order to be able to evaluate terms in the REPL.

purescript-psci-support defines the Eval type class for this purpose. Instances of Eval are provided for Showable types, and for Eff, so that we can evaluate actions in the REPL. Library implementors might like to provide Eval instances for their own Eff-like types.

PSCi Without Pulp

PSCi can be run directly, by specifying a list of PureScript source files as globs:

psci 'src/**/*.purs' 'bower_components/purescript-*/src/**/*.purs'