[dhall-to-yaml-ng] Default Parameter for function

[buzzerpuzzle]

Hi!

I am wondering how I could set up with default parameter for this testFunction.

I am trying to use below command without test2 parameter and like to have default value test2 as false but do not sure whether dhall could support this kind of intent.

Execution Comand dhall-to-yaml-ng <<< './testFunction.dhall { test = True}'

testFunction.dhall

let testFunction = \(args : { test : Bool, test2 : Bool }) ->
  { a = "123", b = args.test }
in testFunction

Thanks, Len

[buzzerpuzzle]

I fee like I would need to add something like below but still not work

Execution Command dhall-to-yaml-ng <<< './testFunction.dhall testParameter::{test=True}'

testFunction.dhall

let testParameter = {
    Type = { test: Bool, test2: Bool},
    default = { test = False, test2 = False}
}

let testFunction = \(args : {test: Bool, test2: Bool}) ->
  { a = "123", b = args.test }
in testFunction

[mmhat]

Hi Len! Regarding your first post: This doesn't work because { test = True } is of type { test : Bool } whereas the expected args argument is of type { test : Bool, test2 : Bool } }. Dhall will note the missing test2 field and complain accordingly.

Regarding your second post: The content of the testFunction.dhall is equivalent to

let testParameter = {   Type = { test: Bool, test2: Bool},  default = { test = False, test2 = False} }

in \(args : {test: Bool, test2: Bool}) -> { a = "123", b = args.test }

as the testFunction at the right-hand-side of the in will be substituted by its definition. This in turn is equivalent to

\(args : {test: Bool, test2: Bool}) -> { a = "123", b = args.test }

since testParameter is never used at the right-hand side of the in.

So what you can do for example is something like:

-- testFunction.dhall
\(args : {test: Bool, test2: Bool}) -> { a = "123", b = args.test }

-- testSchema.dhall
{   Type = { test: Bool, test2: Bool},  default = { test = False, test2 = False} }

-- myTest.dhall
./testFunction.dhall ( ./testSchema.dhall )::{ test2 = Bool }

[mmhat]

Besides: The testFunction.dhall in your second post looks like you wanted to "export " both testParameter and testFunction from that file. You can do this like

-- testFunction.dhall

let testParameter = {
    Type = { test: Bool, test2: Bool},
    default = { test = False, test2 = False}
}

let testFunction = \(args : {test: Bool, test2: Bool}) ->
  { a = "123", b = args.test }

in { testParameter, testFunction }

and evaluate it like dhall <<< "( ./testFunction.dhall ).testFunction ( ./testFunction.dhall ).testParameter::{ test2 = Bool }"

[buzzerpuzzle]

Thanks for your input and it is totally match what I need!