X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fghci.xml;h=528a6522894263ca5089928396e85ee46415b70b;hb=d2b3daa3cc474e6ab010fb6af5c21ddb852b8b5b;hp=82ee33054d6bdbeda1f1b04cc26730a7abfac83f;hpb=8fcfc8d6e42ea5bf49422024bc71d3728ee97db9;p=ghc-hetmet.git diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml index 82ee330..528a652 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 @@ -929,6 +963,7 @@ 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 +983,13 @@ 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 +1059,7 @@ right :: [a] The execution continued at the point it previously stopped, and has now stopped at the breakpoint for a second time. + Setting breakpoints @@ -1109,8 +1152,10 @@ right :: [a] bug. GHCi offers two variants of stepping. Use :step to enable all the breakpoints in the program, and execute until the next breakpoint is - reached. Use :stepover to step over function - applications, which of course are executed all the same. + reached. Use :steplocal to limit the set + of enabled breakpoints to those in the current top level function. + Similarly, use :stepmodule to single step only on + breakpoints contained in the current module. For example: @@ -1122,51 +1167,12 @@ _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. - - In the current version of the debugger, :stepover - is limited to work locally in the lexical sense, that is in the context - of the current expression body. - When you run to the end of the expression, :stepover - stops working and switches to behave like regular :step. - This means - that it will fail to step over the last function application. As a result, - currently :stepover works great for monadic code, but - interacts less perfectly with pure code. For example, if stopped at the - line 2, on the entire expression - qsort left ++ [a] ++ qsort right: - -... [qsort2.hs:2:15-46] *Main> :step -Stopped at qsort2.hs:2:15-46 - -... [qsort2.hs:2:15-46] *Main> :list -2 qsort (a:as) = qsort left ++ [a] ++ qsort right - - - The first :stepover will step over the first - qsort recursive call, as expected. The second one - will step over the evaluation of [a], again as - expected. However, the third one has lexically run out - of the current expression, and will behave like regular - :step, performing one step of lazy evaluation and - stopping at the next breakpoint. In this case it is indeed the second - recursive application of qsort. - -[qsort2.hs:2:36-46] *Main> :stepover -Warning: no more breakpoints in this function body, switching to :step -Stopped at qsort2.hs:(1,0)-(3,55) - -[qsort2.hs:2:36-46] *Main> :list -_result :: [a] -1 qsort [] = [] -2 qsort (a:as) = qsort left ++ [a] ++ qsort right -3 where (left,right) = (filter (<=a) as, filter (>a) as) - + The :list command is particularly useful when - single-stepping, to see where you currently are, as just shown - in the above example. + single-stepping, to see where you currently are: [qsort.hs:5:7-47] *Main> :list @@ -1372,9 +1378,13 @@ 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: @@ -1427,7 +1437,7 @@ 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 @@ -1528,10 +1538,6 @@ Just 20 CAF (e.g. main), stop at a breakpoint, and ask for the value of the CAF at the prompt again. - :stepover only works lexically locally, in the - body of the current expression. As a result, it can be rather impredictable - when used in pure functional code, as opposed to monadic code. - Implicit parameters (see ) are only available at the scope of a breakpoint if there is an explicit type signature. @@ -1708,22 +1714,58 @@ $ 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. + @@ -1785,7 +1827,7 @@ $ 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 @@ -1796,26 +1838,27 @@ $ 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 @@ -1859,6 +1902,12 @@ 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. @@ -1942,6 +1991,17 @@ Prelude> :. cmds.ghci + + : + : + + + Repeat the previous command. + + + + + :history [num] :history @@ -2133,10 +2193,11 @@ 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. @@ -2259,6 +2320,28 @@ 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