WIP: call stored pprocedures that emit plain text

The beginning of #114

src/PostgREST/PgQuery.hs

@@ -10,6 +10,7 @@ import qualified Hasql.Postgres as P
 import qualified Hasql.Backend as B
 
 import qualified Data.Text as T
+import qualified Data.HashMap.Strict as H
 import Text.Regex.TDFA ( (=~) )
 import qualified Network.HTTP.Types.URI as Net
 import qualified Data.ByteString.Char8 as BS
@@ -172,6 +173,13 @@ update t cols vals = B.Stmt
     <> ")")
   empty True
 
+callProc :: QualifiedIdentifier -> JSON.Object -> PStmt
+callProc qi params = do
+  let args = T.intercalate "," $ map assignment (H.toList params)
+  B.Stmt ("select " <> fromQi qi <> "(" <> args <> ")") empty True
+  where
+    assignment (n,v) = pgFmtIdent n <> ":=" <> insertableValue v
+
 wherePred :: QualifiedIdentifier -> Net.QueryItem -> PStmt
 wherePred table (col, predicate) =
   B.Stmt (" " <> pgFmtJsonbPath table (cs col) <> " " <> op <> " " <>