On 16 February 2017 at 07:22, Anthony Clayden <anthony_clayden@clear.net.nz> wrote:

> On 15 February 2017 at 23:06 Harendra Kumar wrote:

>> On 16 February 2017 at 02:31, Anthony Clayden wrote:

For gathering params to a function, I see no need for
extensible records.
The params are known at compile time.
If for a DSL you want 'optional' fields, make them Maybe's,
with a default of Nothing.

The point is - I do not want the user to specify all parameters explicitly. There may be a whole bunch of optional parameters in the record but only a few are to be specified in general. I do not want 2 values and 10 Nothings or explicit defaults there.

>
> I am trying to write a program which provides a friendly
> high level DSL to the user.

'user' here seems to mean programmer,
if you're looking for static guarantees.

Yes, but more of a declarative programmer.

> I want a pure function like
> API but instead of passing positional parameters I want
> the user to be able to specify arguments based on keywords
> and be able to skip any optional arguments. Something like
> the following, name is mandatory and email is optional:
>
> maintainer (#name := "Harendra Kumar", #email :=
> "xyz@gmail.com")
>
> I can achieve this using rawr. The argument to the
> function is an anonymous record ...

OK. But I'm not seeing why it has to be anonymous.
Again, if it's for a specific function, it needs specific
parameters.
An anonymous record might provide keywords not valid,
as well as fail to provide keywords expected.

It does not necessarily have to be anonymous. But I see no problem if it is anonymous. Type checking catches missing keywords or invalid keywords. The example I gave does not have correct type constraints but by fixing it you cannot give it incorrect keywords, I just tested it.

-harendra