implement extract

Language/SQL/SimpleSQL/Parser.lhs

@@ -172,6 +172,13 @@ to be.
 >     prefixCast = try (CastOp <$> typeName
 >                              <*> stringLiteral)
 
+> extract :: P ScalarExpr
+> extract = try (keyword_ "extract") >>
+>     parens (makeOp <$> identifierString
+>                    <*> (keyword_ "from"
+>                         *> scalarExpr'))
+>   where makeOp n e = SpecialOp "extract" [Iden n, e]
+
 > inSuffix :: ScalarExpr -> P ScalarExpr
 > inSuffix e =
 >     In
@@ -289,7 +296,7 @@ postgresql handles this
 >     factor = choice [literal
 >                     ,scase
 >                     ,cast
->                     --,extract
+>                     ,extract
 >                     ,subquery
 >                     ,prefixUnaryOp
 >                     ,try app

Language/SQL/SimpleSQL/Pretty.lhs

@@ -35,6 +35,11 @@ back into SQL source text. It attempts to format the output nicely.
 >       ,text nm <+> scalarExpr b
 >       ,text "and" <+> scalarExpr c]
 
+> scalarExpr (SpecialOp "extract" [a,n]) =
+>   text "extract" <> parens (scalarExpr a
+>                             <+> text "from"
+>                             <+> scalarExpr n)
+
 > scalarExpr (SpecialOp nm es) =
 >   text nm <+> parens (commaSep $ map scalarExpr es)
 

Tests.lhs

@@ -168,7 +168,7 @@
 >     ,("a is similar to b", BinOp "is similar to" (Iden "a") (Iden "b"))
 >     ,("a is not similar to b", BinOp "is not similar to" (Iden "a") (Iden "b"))
 >     ,("a overlaps b", BinOp "overlaps" (Iden "a") (Iden "b"))
->     --,("extract(day from t)", SpecialOp "extract" [Iden "day", Iden "t"])
+>     ,("extract(day from t)", SpecialOp "extract" [Iden "day", Iden "t"])
 >     ]
 
 > aggregates :: TestItem