X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fdocs%2Fusers_guide%2Fghci.sgml;h=792f68b68f6505d0b4269af70bf92b9163fa7bb1;hb=dc6afe4242238aa1a7a5d3a150a346d23dd6ea22;hp=0ba4d8da401c1054fdaf7eb2c1248a496b53a61a;hpb=f50c833a105e6c7f44c5c43a364dc4ee1803a198;p=ghc-hetmet.git diff --git a/ghc/docs/users_guide/ghci.sgml b/ghc/docs/users_guide/ghci.sgml index 0ba4d8d..792f68b 100644 --- a/ghc/docs/users_guide/ghci.sgml +++ b/ghc/docs/users_guide/ghci.sgml @@ -63,6 +63,7 @@ Prelude> :show bindings show the current bindings made at the prompt :type <expr> show the type of <expr> + :kind <type> show the kind of <type> :undef <cmd> undefine user-defined command :<cmd> :unset <option> ... unset options :quit exit GHCi @@ -162,7 +163,7 @@ Ok, modules loaded: Main. indirectly, by the topmost module, and load them all in dependency order. - + Modules vs. filenames modulesand filenames filenamesof modules @@ -196,7 +197,7 @@ Ok, modules loaded: Main. source files, whereas in standard batch-compilation mode the option is used to specify the search path for interface files, see . + linkend="search-path">. One consequence of the way that GHCi follows dependencies to find modules to load is that every module must have a source @@ -207,10 +208,6 @@ Ok, modules loaded: Main. which GHCi can't find a source file, even if there are object and interface files for the module, you'll get an error message. - - One final note: if you load a module called Main, it must - contain a main function, just like in - GHC. @@ -641,6 +638,33 @@ Wed Mar 14 12:23:13 GMT 2001 of it is lost. + + + Type defaulting in GHCi + Type default + Show class + + Consider this GHCi session: + + ghci> reverse [] + + What should GHCi do? Strictly speaking, the program is ambiguous. show (reverse []) + (which is what GHCi computes here) has type Show a => a and how that displays depends + on the type a. For example: + + ghci> (reverse []) :: String + "" + ghci> (reverse []) :: [Int] + [] + + However, it is tiresome for the user to have to specify the type, so GHCi extends Haskell's type-defaulting + rules (Section 4.3.4 of the Haskell 98 Report (Revised)) as follows. If the expression yields a set of + type constraints that are all from standard classes (Num, Eq etc.), + and at least one is either a numeric class or the Show, + Eq, or Ord class, + GHCi will try to use one of the default types, just as described in the Report. + + @@ -672,26 +696,33 @@ $ ghci Main.hs Packages packageswith GHCi - GHCi can make use of all the packages that come with GHC, - For example, to start up GHCi with the network - package loaded: + Most packages (see ) are + available without needing to specify any extra flags at all: + they will be automatically loaded the first time they are + needed. + + For non-auto packages, however, you need to request the + package be loaded by using the -package flag: -$ ghci -package network +$ ghci -package data ___ ___ _ / _ \ /\ /\/ __(_) - / /_\// /_/ / / | | GHC Interactive, version 5.04, for Haskell 98. + / /_\// /_/ / / | | GHC Interactive, version 5.05, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. -Loading package network ... linking ... done. +Loading package lang ... linking ... done. +Loading package concurrent ... linking ... done. +Loading package readline ... linking ... done. +Loading package unix ... linking ... done. +Loading package posix ... linking ... done. +Loading package util ... linking ... done. +Loading package data ... linking ... done. Prelude> - - - Note that GHCi will also automatically load any packages - on which the requested package depends. + The following command works to load new packages into a running GHCi: @@ -702,7 +733,7 @@ Prelude> :set -package name But note that doing this will cause all currently loaded modules to be unloaded, and you'll be dumped back into the - Prelude. + Prelude. @@ -711,7 +742,10 @@ Prelude> :set -package name Extra libraries may be specified on the command line using the normal -llib - option. For example, to load the “m” library: + option. (The term library here refers to + libraries of foreign object code; for using libraries of Haskell + source code, see .) For + example, to load the “m” library: $ ghci -lm @@ -745,6 +779,10 @@ $ ghci -lm (.o or .obj depending on your platform) from the command-line. Just add the name the object file to the command line. + + Ordering of options matters: a library + should be mentioned before the libraries it + depends on (see ). @@ -804,6 +842,12 @@ $ ghci -lm beginning of dir will be replaced by the contents of the environment variable HOME. + + NOTE: changing directories causes all currently loaded + modules to be unloaded. This is because the search path is + usually expressed using relative directories, and changing + the search path in the middle of a session is not + supported. @@ -1020,6 +1064,17 @@ Prelude> :def make (\_ -> return ":! ghc ––make Main") + :kind type + :kind + + Infers and prints the kind of + type. The latter can be an arbitrary + type expression, including a partial application of a type constructor, + such as Either Int. + + + + :undef name :undef @@ -1222,22 +1277,6 @@ Prelude> :set -fno-glasgow-exts - GHCi complains about main not being - in scope when I load a module. - mainwith GHCi - - - You probably omitted the module - declaration at the top of the module, which causes the - module name to default to Main. In - Haskell, the Main module must define a - function called main. Admittedly this - doesn't make a great deal of sense for an interpreter, but - the rule was kept for compatibility with GHC. - - - - The interpreter can't load modules with foreign export declarations!