X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fghci.xml;h=9fa5d875b0326c6a7f29ebee337aec01452435d3;hb=c24bd1bbbdc4e20ea5c31b8779a70a5421f44962;hp=69078d5093ebb2e0489bf0d06d74a7f16594cdc1;hpb=3240dc3b54438e55cdbc7d449aeaaad705bbb653;p=ghc-hetmet.git diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml index 69078d5..9fa5d87 100644 --- a/docs/users_guide/ghci.xml +++ b/docs/users_guide/ghci.xml @@ -368,7 +368,6 @@ hello IO monad. Prelude> x <- return 42 -42 Prelude> print x 42 Prelude> @@ -380,7 +379,8 @@ Prelude> x in future statements, for example to print it as we did above. - GHCi will print the result of a statement if and only if: + If is set then + GHCi will print the result of a statement if and only if: The statement is not a binding, or it is a monadic binding @@ -393,13 +393,8 @@ Prelude> Show - The automatic printing of binding results can be supressed with - (this does not - supress printing the result of non-binding statements). - . - You might want to do this to prevent the result of binding - statements from being fully evaluated by the act of printing - them, for example. + . + Of course, you can also bind normal non-IO expressions using the let-statement: @@ -424,6 +419,45 @@ Prelude> Note that let bindings do not automatically print the value bound, unlike monadic bindings. + Hint: you can also use let-statements + to define functions at the prompt: + +Prelude> let add a b = a + b +Prelude> add 1 2 +3 +Prelude> + + However, this quickly gets tedious when defining functions + with multiple clauses, or groups of mutually recursive functions, + because the complete definition has to be given on a single line, + using explicit braces and semicolons instead of layout: + +Prelude> let { f op n [] = n ; f op n (h:t) = h `op` f op n t } +Prelude> f (+) 0 [1..3] +6 +Prelude> + + To alleviate this issue, GHCi commands can be split over + multiple lines, by wrapping them in :{ and + :} (each on a single line of its own): + +Prelude> :{ +Prelude| let { g op n [] = n +Prelude| ; g op n (h:t) = h `op` g op n t +Prelude| } +Prelude| :} +Prelude> g (*) 1 [1..3] +6 + + Such multiline commands can be used with any GHCi command, + and the lines between :{ and + :} are simply merged into a single line for + interpretation. That implies that each such group must form a single + valid command when merged, and that no layout rule is used. + The main purpose of multiline commands is not to replace module + loading but to make definitions in .ghci-files (see ) more readable and maintainable. + Any exceptions raised during the evaluation or execution of the statement are caught and printed by the GHCi command line interface (for more information on exceptions, see the module @@ -577,7 +611,7 @@ Prelude IO> - The <literal>:main</literal> command + The <literal>:main</literal> and <literal>:run</literal> commands When a program is compiled and executed, it can use the @@ -602,6 +636,37 @@ Prelude> :main foo bar ["foo","bar"] + + We can also quote arguments which contains characters like + spaces, and they are treated like Haskell strings, or we can + just use Haskell list syntax: + + + +Prelude> :main foo "bar baz" +["foo","bar baz"] +Prelude> :main ["foo", "bar baz"] +["foo","bar baz"] + + + + Finally, other functions can be called, either with the + -main-is flag or the :run + command: + + + +Prelude> let foo = putStrLn "foo" >> System.Environment.getArgs >>= print +Prelude> let bar = putStrLn "bar" >> System.Environment.getArgs >>= print +Prelude> :set -main-is foo +Prelude> :main foo "bar baz" +foo +["foo","bar baz"] +Prelude> :run bar ["foo", "bar baz"] +bar +["foo","bar baz"] + + @@ -929,6 +994,7 @@ right :: [a] left: +[qsort.hs:2:15-46] *Main> :set -fprint-evld-with-show [qsort.hs:2:15-46] *Main> :print left left = (_t1::[a]) @@ -948,6 +1014,13 @@ left = (_t1::[a]) underscore, in this case _t1. + The flag -fprint-evld-with-show instructs + :print to reuse + available Show instances when possible. This happens + only when the contents of the variable being inspected + are completely evaluated. + + If we aren't concerned about preserving the evaluatedness of a variable, we can use :force instead of :print. The :force command @@ -1017,6 +1090,7 @@ right :: [a] The execution continued at the point it previously stopped, and has now stopped at the breakpoint for a second time. + Setting breakpoints @@ -1124,7 +1198,7 @@ _result :: IO () The command :step expr begins the evaluation of expr in single-stepping mode. If - expr is ommitted, then it single-steps from + expr is omitted, then it single-steps from the current breakpoint. :stepover works similarly. @@ -1335,9 +1409,13 @@ a :: a :trace and :history to establish the context. However, head is in a library and we can't set a breakpoint on it directly. For this reason, GHCi - provides the flag -fbreak-on-exception which causes - the evaluator to stop when an exception is thrown, just as it does when - a breakpoint is hit. This is only really useful in conjunction with + provides the flags -fbreak-on-exception which causes + the evaluator to stop when an exception is thrown, and + -fbreak-on-error, which works similarly but stops only on + uncaught exceptions. When stopping at an exception, GHCi will act + just as it does when a breakpoint is hit, with the deviation that it + will not show you any source code location. Due to this, these + commands are only really useful in conjunction with :trace, in order to log the steps leading up to the exception. For example: @@ -1390,7 +1468,7 @@ as = 'b' : 'c' : (_t1::[Char]) import Prelude hiding (map) -map :: (a->b) -> a -> b +map :: (a->b) -> [a] -> [b] map f [] = [] map f (x:xs) = f x : map f xs @@ -1667,22 +1745,58 @@ $ ghci -lm - :browse *module ... + :browse! *module ... :browse Displays the identifiers defined by the module module, which must be either - loaded into GHCi or be a member of a package. If the - * symbol is placed before the module - name, then all the identifiers defined - in module are shown; otherwise - the list is limited to the exports of + loaded into GHCi or be a member of a package. If + module is omitted, the most + recently-loaded module is used. + + If the * symbol is placed before + the module name, then all the + identifiers in scope in module are + shown; otherwise the list is limited to the exports of module. The *-form is only available for modules which are interpreted; for compiled modules (including modules from packages) only the non-* - form of :browse is available. + form of :browse is available. + If the ! symbol is appended to the + command, data constructors and class methods will be + listed individually, otherwise, they will only be listed + in the context of their data type or class declaration. + The !-form also annotates the listing + with comments giving possible imports for each group of + entries. + +Prelude> :browse! Data.Maybe +-- not currently imported +Data.Maybe.catMaybes :: [Maybe a] -> [a] +Data.Maybe.fromJust :: Maybe a -> a +Data.Maybe.fromMaybe :: a -> Maybe a -> a +Data.Maybe.isJust :: Maybe a -> Bool +Data.Maybe.isNothing :: Maybe a -> Bool +Data.Maybe.listToMaybe :: [a] -> Maybe a +Data.Maybe.mapMaybe :: (a -> Maybe b) -> [a] -> [b] +Data.Maybe.maybeToList :: Maybe a -> [a] +-- imported via Prelude +Just :: a -> Maybe a +data Maybe a = Nothing | Just a +Nothing :: Maybe a +maybe :: b -> (a -> b) -> Maybe a -> b + + + This output shows that, in the context of the current session, in the scope + of Prelude, the first group of items from + Data.Maybe have not been imported (but are available in + fully qualified form in the GHCi session - see ), whereas the second group of items have been + imported via Prelude and are therefore available either + unqualified, or with a Prelude. qualifier. + @@ -1744,7 +1858,7 @@ $ ghci -lm Generates a “tags” file for Vi-style editors (:ctags) or Emacs-style editors (:etags). If - no filename is specified, the defaulit tags or + no filename is specified, the default tags or TAGS is used, respectively. Tags for all the functions, constructors and types in the currently loaded modules are created. All modules must @@ -1755,26 +1869,27 @@ $ ghci -lm - :def name expr + :def! name expr :def - The command :def - name - expr defines a new GHCi command - :name, - implemented by the Haskell expression - expr, which must have type - String -> IO String. When - :name - args is typed at the - prompt, GHCi will run the expression - (name - args), take the - resulting String, and feed it back into - GHCi as a new sequence of commands. Separate commands in - the result must be separated by - ‘\n’. + :def is used to define new + commands, or macros, in GHCi. The command + :def name + expr defines a new GHCi command + :name, + implemented by the Haskell expression + expr, which must have type + String -> IO String. When + :name + args is typed at the + prompt, GHCi will run the expression + (name + args), take the + resulting String, and feed it back into + GHCi as a new sequence of commands. Separate commands in + the result must be separated by + ‘\n’. That's all a little confusing, so here's a few examples. To start with, here's a new GHCi command which @@ -1818,6 +1933,12 @@ Prelude> :. cmds.ghci :., by analogy with the ‘.’ Unix shell command that does the same thing. + + Typing :def on its own lists the + currently-defined macros. Attempting to redefine an + existing command name results in an error unless the + :def! form is used, in which case the old + command with that name is silently overwritten. @@ -1901,6 +2022,17 @@ Prelude> :. cmds.ghci + + : + : + + + Repeat the previous command. + + + + + :history [num] :history @@ -2018,6 +2150,37 @@ Prelude> :main foo bar ["foo","bar"] + + We can also quote arguments which contains characters like + spaces, and they are treated like Haskell strings, or we can + just use Haskell list syntax: + + + +Prelude> :main foo "bar baz" +["foo","bar baz"] +Prelude> :main ["foo", "bar baz"] +["foo","bar baz"] + + + + Finally, other functions can be called, either with the + -main-is flag or the :run + command: + + + +Prelude> let foo = putStrLn "foo" >> System.Environment.getArgs >>= print +Prelude> let bar = putStrLn "bar" >> System.Environment.getArgs >>= print +Prelude> :set -main-is foo +Prelude> :main foo "bar baz" +foo +["foo","bar baz"] +Prelude> :run bar ["foo", "bar baz"] +bar +["foo","bar baz"] + + @@ -2092,10 +2255,11 @@ Prelude> :main foo bar :set - Sets various options. See - for a list of available options. The - :set command by itself shows which - options are currently set. + Sets various options. See for a list of + available options and for a + list of GHCi-specific flags. The :set command by + itself shows which options are currently set. It also lists the current + dynamic flag settings, with GHCi-specific flags listed separately. @@ -2218,6 +2382,28 @@ Prelude> :main foo bar + :show packages + :show packages + + + Show the currently active package flags, as well as the list of + packages currently loaded. + + + + + + :show languages + :show languages + + + Show the currently active language flags. + + + + + + :show [args|prog|prompt|editor|stop] :show