diff options
| -rw-r--r-- | ghc/docs/users_guide/glasgow_exts.sgml | 18 |
1 files changed, 12 insertions, 6 deletions
diff --git a/ghc/docs/users_guide/glasgow_exts.sgml b/ghc/docs/users_guide/glasgow_exts.sgml index 025a92387e..baf9ef747a 100644 --- a/ghc/docs/users_guide/glasgow_exts.sgml +++ b/ghc/docs/users_guide/glasgow_exts.sgml @@ -1598,7 +1598,7 @@ declarations </programlisting> "overlap" if <literal>type1</literal> and <literal>type2</literal> unify. - +</para> <para> However, if you give the command line option <option>-fallow-overlapping-instances</option><indexterm><primary>-fallow-overlapping-instances @@ -3184,6 +3184,12 @@ the background to the main technical innovations is discussed in "<ulink url="http://research.microsoft.com/~simonpj/papers/meta-haskell"> Template Meta-programming for Haskell</ulink>" (Proc Haskell Workshop 2002). +The details of the Template Haskell design are still in flux. Make sure you +consult the <ulink url="http://www.haskell.org/ghc/docs/latest/html/libraries/index.html">online library reference material</ulink> +(search for the type ExpQ). +[Temporary: many changes to the original design are described in + <ulink url="http://research.microsoft.com/~simonpj/tmp/notes2.ps">"http://research.microsoft.com/~simonpj/tmp/notes2.ps"</ulink>. +Not all of these changes are in GHC 6.2.] </para> <para> The first example from that paper is set out below as a worked example to help get you started. @@ -3289,6 +3295,7 @@ Tim Sheard is going to expand it.) First cut and paste the two modules below into "Main.hs" and "Printf.hs":</para> <programlisting> + {- Main.hs -} module Main where @@ -3299,9 +3306,8 @@ import Printf ( pr ) -- generated at compile time by "pr" and splices it into -- the argument of "putStrLn". main = putStrLn ( $(pr "Hello") ) -</programlisting> -<programlisting> + {- Printf.hs -} module Printf where @@ -3324,14 +3330,14 @@ parse s = [ L s ] -- Generate Haskell source code from a parsed representation -- of the format string. This code will be spliced into -- the module which calls "pr", at compile time. -gen :: [Format] -> Expr +gen :: [Format] -> ExpQ gen [D] = [| \n -> show n |] gen [S] = [| \s -> s |] -gen [L s] = string s +gen [L s] = stringE s -- Here we generate the Haskell code for the splice -- from an input format string. -pr :: String -> Expr +pr :: String -> ExpQ pr s = gen (parse s) </programlisting> |