Let's start with an example GHCi session. You can fire up
GHCi with the command ghci:
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 5.04, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base ... linking ... done.
Loading package haskell98 ... linking ... done.
There may be a short pause while GHCi loads the prelude and
standard libraries, after which the prompt is shown. If we follow
the instructions and type :? for help, we
Commands available from the prompt:
<stmt> evaluate/run <stmt>
:add <filename> ... add module(s) to the current target set
:browse [*]<module> display the names defined by <module>
:cd <dir> change directory to <dir>
:def <cmd> <expr> define a command :<cmd>
:help, :? display this list of commands
:info [<name> ...] display information about the given names
:load <filename> ... load module(s) and their dependents
:module [+/-] [*]<mod> ... set the context for expression evaluation
:reload reload the current module set
:set <option> ... set options
:set args <arg> ... set the arguments returned by System.getArgs
:set prog <progname> set the value returned by System.getProgName
:show modules show the currently loaded modules
:show bindings show the current bindings made at the prompt
:type <expr> show the type of <expr>
:undef <cmd> undefine user-defined command :<cmd>
:unset <option> ... unset options
:quit exit GHCi
:!<command> run the shell command <command>
Options for `:set' and `:unset':
+r revert top-level expressions after each evaluation
+s print timing/memory stats after each evaluation
+t print type after evaluation
-<flags> most GHC command line flags can also be set here
(eg. -v2, -fglasgow-exts, etc.)
We'll explain most of these commands as we go along. For
Hugs users: many things work the same as in Hugs, so you should be
able to get going straight away.
Haskell expressions can be typed at the prompt:
Prelude> let x = 42 in x / 9
GHCi interprets the whole line as an expression to evaluate.
The expression may not span several lines - as soon as you press
enter, GHCi will attempt to evaluate it.