[Ur] Need help with desugaring dml

[Adam Chlipala]

The key things missing in the original functor argument are a folder for 
[u] and a record of [sql_injectable] instances for it, both of which 
you'll see used in similar UPO functions mentioned earlier.

BTW, the type of [insert] (in lib/ur/basis.urs) isn't magic and can be 
inspected just like any Ur type, and it should be possible to understand 
from first principles.

On 02/11/2017 04:19 AM, fold at tuta.io wrote:
> Actually, it might be quite simple.
> Incomplete, but, hopefully, clear example:
>
> table tab : $([Ix = int] ++ someColumns ++ otherColumns) PRIMARY KEY Ix
>
> fun test () : transaction xbody =
>     <...>
>     tn <- now;
>     easy_insert tab ({Ix = ix} ++ field_defaults ++ {Dated = tn});
>     <...>
>
>
>
> 11. Feb 2017 22:09 by fold at tuta.io <mailto:fold at tuta.io>:
>
>     Sergey,
>
>     Something similar to this:
>     https://github.com/achlipala/upo/blob/master/sql.ur#L44
>     and this:
>     https://github.com/achlipala/upo/blob/master/sql.ur#L50
>     might help you a bit.
>
>     Also check other functions in sql.ur
>
>     I believe you also can figure out desugared type expressions from
>     compiler error output if you replace parts of your code with
>     simple expressions of known type.
>
>     https://wiki.haskell.org/GHC/Typed_holes
>
>
>
>
>
>     11. Feb 2017 21:18 by grrwlf at gmail.com <mailto:grrwlf at gmail.com>:
>
>         Hi. I'm trying (again) to write an Ur/Web module to provide
>         API for
>         managing OS-level processes. I expect users to pass it a table
>         containing _at_least_ id, process command name, arguments,
>         placeholder
>         for exit code and status string. It is expected that users
>         will use
>         tables containing more problem-specific columns.
>
>         The problem is that I cant use simple dml operations anymore. As a
>         start, I tried to write dummy insert using [demo/more/orm.ur] as
>         example, but was stopped by difficult [ensql] function. Could you
>         please help me to implement it? The code is quite short and listed
>         below.
>
>         Regards,
>         Sergey
>
>         ---
>
>         con jobinfo = [
>         Id = int
>         , ExitCode = option int
>         , Cmd = string
>         , Hint = string
>         ]
>
>         functor Make(M : sig
>
>         con u
>
>         constraint [Id,ExitCode,Cmd,Hint] ~ u
>
>         table t : (jobinfo ++ u)
>
>         sequence s
>
>         end) = struct
>
>         open CallbackFFI
>
>         type row' = record (jobinfo ++ M.u)
>
>         (* fun ensql [avail ::_] (r : row') : $(map (sql_exp avail []
>         []) fs') = *)
>         (* @map2 [meta] [fst] [fn ts :: (Type * Type) => sql_exp avail
>         [] [] ts.1] *)
>         (* (fn [ts] meta v => @sql_inject meta.Inj v) *)
>         (* M.folder M.cols r *)
>
>         (* createSync will start the job, but in this example it just
>         does a
>         simple insert.
>         args is a problem-specific part of the table record.
>
>         How to make this dml(insert..) work? *)
>
>         fun createSync (ji : record jobinfo, args : record M.u) :
>         transaction (option int) =
>         i <- nextval M.s;
>         dml(insert M.t ({Id = sql_inject ji.Id,
>         ExitCode = sql_inject ji.ExitCode,
>         Cmd = sql_inject ji.Cmd,
>         Hint = sql_inject ji.Hint} ++ (ensql args) ));
>
>         return (Some i)
>
>         end
>

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