X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fghci.xml;h=528a6522894263ca5089928396e85ee46415b70b;hb=d2b3daa3cc474e6ab010fb6af5c21ddb852b8b5b;hp=3ba2012eee34a086f7cd4ac1cb7fa227c7f6c1a5;hpb=5263c9ab4408e3b62dbf7505ab40a81946d4e49b;p=ghc-hetmet.git
diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml
index 3ba2012..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 suppressed with
- (this does not
- suppress 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
@@ -1403,7 +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
@@ -1680,7 +1714,7 @@ $ ghci -lm
- :browse*module ...
+ :browse!*module ...
:browse
@@ -1698,7 +1732,40 @@ $ ghci -lm
*-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.
+
@@ -1771,26 +1838,27 @@ $ ghci -lm
- :defnameexpr
+ :def!nameexpr: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
+ :defname
+ 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
@@ -1834,6 +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.
@@ -1917,6 +1991,17 @@ Prelude> :. cmds.ghci
+
+ :
+ :
+
+
+ Repeat the previous command.
+
+
+
+
+
:history [num]:history
@@ -2108,10 +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.
@@ -2234,6 +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