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Diffstat (limited to 'docs/users_guide/ghci.xml')
| -rw-r--r-- | docs/users_guide/ghci.xml | 41 |
1 files changed, 24 insertions, 17 deletions
diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml index 28e9972b24..b092953b36 100644 --- a/docs/users_guide/ghci.xml +++ b/docs/users_guide/ghci.xml @@ -1817,26 +1817,27 @@ $ ghci -lm <varlistentry> <term> - <literal>:def</literal> <replaceable>name</replaceable> <replaceable>expr</replaceable> + <literal>:def<optional>!</optional> <optional><replaceable>name</replaceable> <replaceable>expr</replaceable></optional></literal> <indexterm><primary><literal>:def</literal></primary></indexterm> </term> <listitem> - <para>The command <literal>:def</literal> - <replaceable>name</replaceable> - <replaceable>expr</replaceable> defines a new GHCi command - <literal>:<replaceable>name</replaceable></literal>, - implemented by the Haskell expression - <replaceable>expr</replaceable>, which must have type - <literal>String -> IO String</literal>. When - <literal>:<replaceable>name</replaceable> - <replaceable>args</replaceable></literal> is typed at the - prompt, GHCi will run the expression - <literal>(<replaceable>name</replaceable> - <replaceable>args</replaceable>)</literal>, take the - resulting <literal>String</literal>, and feed it back into - GHCi as a new sequence of commands. Separate commands in - the result must be separated by - ‘<literal>\n</literal>’.</para> + <para><literal>:def</literal> is used to define new + commands, or macros, in GHCi. The command + <literal>:def</literal> <replaceable>name</replaceable> + <replaceable>expr</replaceable> defines a new GHCi command + <literal>:<replaceable>name</replaceable></literal>, + implemented by the Haskell expression + <replaceable>expr</replaceable>, which must have type + <literal>String -> IO String</literal>. When + <literal>:<replaceable>name</replaceable> + <replaceable>args</replaceable></literal> is typed at the + prompt, GHCi will run the expression + <literal>(<replaceable>name</replaceable> + <replaceable>args</replaceable>)</literal>, take the + resulting <literal>String</literal>, and feed it back into + GHCi as a new sequence of commands. Separate commands in + the result must be separated by + ‘<literal>\n</literal>’.</para> <para>That's all a little confusing, so here's a few examples. To start with, here's a new GHCi command which @@ -1880,6 +1881,12 @@ Prelude> :. cmds.ghci <literal>:.</literal>, by analogy with the ‘<literal>.</literal>’ Unix shell command that does the same thing.</para> + + <para>Typing <literal>:def</literal> on its own lists the + currently-defined macros. Attempting to redefine an + existing command name results in an error unless the + <literal>:def!</literal> form is used, in which case the old + command with that name is silently overwritten.</para> </listitem> </varlistentry> |