Functional Programming with Haskell - Interacting with Haskell

본격적인 내용에 앞서 사용중인 운영체제에 맞게 아래에서 다운로드하여 설치한다.

https://www.haskell.org/downloads

설치 후 CMD, BASH 또는 WinGHCi, GHCi 에서 ghci 를 실행한다. 

root@gcloudx:~# ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Prelude> 

표준 프롬프트는 Prelude> 이다. 아래와 같이 프롬프트를 설정할 수도 있다.

root@gcloudx:~# ghci
GHCi, version 7.10.3: http://www.haskell.org/ghc/  :? for help
Prelude> :set prompt ">"
>
>
>
 

가능한 명령어 목록은 :help 를 통해서 확인할 수 있다.

>:help
 Commands available from the prompt:
 
   <statement>                 evaluate/run <statement>
   :                           repeat last command
   :{\n ..lines.. \n:}\n       multiline command
   :add [*]<module> ...        add module(s) to the current target set
   :browse[!] [[*]<mod>]       display the names defined by module <mod>
                               (!: more details; *: all top-level names)
   :cd <dir>                   change directory to <dir>
   :cmd <expr>                 run the commands returned by <expr>::IO String
   :complete <dom> [<rng>] <s> list completions for partial input string
   :ctags[!] [<file>]          create tags file for Vi (default: "tags")
                               (!: use regex instead of line number)
   :def <cmd> <expr>           define command :<cmd> (later defined command has
                               precedence, ::<cmd> is always a builtin command)
   :edit <file>                edit file
   :edit                       edit last module
   :etags [<file>]             create tags file for Emacs (default: "TAGS")
   :help, :?                   display this list of commands
   :info[!] [<name> ...]       display information about the given names
                               (!: do not filter instances)
   :issafe [<mod>]             display safe haskell information of module <mod>
   :kind[!] <type>             show the kind of <type>
                               (!: also print the normalised type)
   :load [*]<module> ...       load module(s) and their dependents
   :main [<arguments> ...]     run the main function with the given arguments
   :module [+/-] [*]<mod> ...  set the context for expression evaluation
   :quit                       exit GHCi
   :reload                     reload the current module set
   :run function [<arguments> ...] run the function with the given arguments
   :script <filename>          run the script <filename>
   :type <expr>                show the type of <expr>
   :undef <cmd>                undefine user-defined command :<cmd>
   :!<command>                 run the shell command <command>
 
 -- Commands for debugging:
 
   :abandon                    at a breakpoint, abandon current computation
   :back                       go back in the history (after :trace)
   :break [<mod>] <l> [<col>]  set a breakpoint at the specified location
   :break <name>               set a breakpoint on the specified function
   :continue                   resume after a breakpoint
   :delete <number>            delete the specified breakpoint
   :delete *                   delete all breakpoints
   :force <expr>               print <expr>, forcing unevaluated parts
   :forward                    go forward in the history (after :back)
   :history [<n>]              after :trace, show the execution history
   :list                       show the source code around current breakpoint
   :list <identifier>          show the source code for <identifier>
   :list [<module>] <line>     show the source code around line number <line>
   :print [<name> ...]         show a value without forcing its computation
   :sprint [<name> ...]        simplified version of :print
   :step                       single-step after stopping at a breakpoint
   :step <expr>                single-step into <expr>
   :steplocal                  single-step within the current top-level binding
   :stepmodule                 single-step restricted to the current module
   :trace                      trace after stopping at a breakpoint
   :trace <expr>               evaluate <expr> with tracing on (see :history)
 
 -- Commands for changing settings:
 
   :set <option> ...           set options
   :seti <option> ...          set options for interactive evaluation only
   :set args <arg> ...         set the arguments returned by System.getArgs
   :set prog <progname>        set the value returned by System.getProgName
   :set prompt <prompt>        set the prompt used in GHCi
   :set prompt2 <prompt>       set the continuation prompt used in GHCi
   :set editor <cmd>           set the command used for :edit
   :set stop [<n>] <cmd>       set the command to run when a breakpoint is hit
   :unset <option> ...         unset options
 
  Options for ':set' and ':unset':
 
    +m            allow multiline commands
    +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, -XFlexibleInstances, etc.)
                    for GHCi-specific flags, see User's Guide,
                    Flag reference, Interactive-mode options
 
 -- Commands for displaying information:
 
   :show bindings              show the current bindings made at the prompt
   :show breaks                show the active breakpoints
   :show context               show the breakpoint context
   :show imports               show the current imports
   :show linker                show current linker state
   :show modules               show the currently loaded modules
   :show packages              show the currently active package flags
   :show paths                 show the currently active search paths
   :show language              show the currently active language flags
   :show <setting>             show value of <setting>, which is one of
                                  [args, prog, prompt, editor, stop]
   :showi language             show language flags for interactive evaluation
 
>
 

:set +t 를 통해 타입을 확인할 수 있다.

Prelude> :set +t
Prelude> 3 + 4
7
it :: Num a => a

Prelude> 2 ^ 777
794889263257962974796277498092801308291525640763748664903194643469338087775424965801409745320266996710649718116931109481559848982586784968419475084821084743272680947722675151641735826243378403750534655587182832000457137589153821622272
it :: Num a => a

Prelude> "abc" ++ "xyz"
"abcxyz"
it :: [Char]

여기서 "::" 는 "has type" 으로 읽으면 된다. 

그리고 표현식의 값은 it라는 이름으로 바운딩된다. 

그리고 이 it 는 연속적인 계산에 사용 가능하다.

Prelude> 3 + 4
7
it :: Num a => a
Prelude> it + it * it
56
it :: Num a => a
Prelude> it /= it
False
it :: Bool

※ GHCi 사용법에 대한 보다 자세한 내용은 아래 링크 참조

https://downloads.haskell.org/~ghc/5.04/docs/html/users_guide/ghci.html