How can I encode a rule tree of multiple depths in Dhall? - directed-acyclic-graphs

Question

I'm trying to move some error prone YAML into Dhall to make some system configuration simpler. I have a tree that looks like:
composite:
condition: And
rules:
- composite:
condition: And
rules:
- leaf:
static: true
- leaf:
exists: some-property-to-lookup
- composite:
condition: Or
rules:
- composite:
condition: And
rules:
- leaf:
static: true
- leaf:
exists: some-property-to-lookup
I'm trying to encode this in Dhall and I can't seem to provide the compiler the right information. My latest try looks like:
let Field
: Type
= < B : { static : Bool } | S : { exists : Text } >
let Condition
: Type
= < And | Or | Not >
let Node
: Type
= ∀(Node : Type) →
∀(Leaf : { leaf : Field }) →
∀(Branch : { composite : { condition : Condition, rules : List Node } }) →
Node
let example
: Node
= ∀(Node : Type) →
∀(Leaf : { leaf : Field }) →
∀(Branch : { composite : { condition : Condition, rules : List Node } }) →
Branch
{ composite =
{ condition = Condition.And
, rules =
[ Branch
{ composite =
{ condition = Condition.And
, rules = [ Leaf { leaf = Field.S { exists = "hi" } } ]
}
}
, Branch
{ composite =
{ condition = Condition.Or
, rules = [ Leaf { leaf = Field.S { static = true } } ]
}
}
, Branch
{ composite =
{ condition = Condition.And
, rules =
[ Branch
{ composite =
{ condition = Condition.And
, rules =
[ Leaf { leaf = Field.S { exists = "hi" } } ]
}
}
, Branch
{ composite =
{ condition = Condition.Or
, rules =
[ Leaf { leaf = Field.S { static = true } } ]
}
}
]
}
}
]
}
}
in example
But I get Error: Not a function. Any pointers would be appreciated.
I also tried w/ the Graph module, but I can't seem to convert that to YAML directly.

Answer 1

This works:
let Field
: Type
= < B : { static : Bool } | S : { exists : Text } >
let Condition
: Type
= < And | Or | Not >
let Node
: Type
= ∀(Node : Type) →
∀(Leaf : { leaf : Field } → Node) →
∀(Branch : { composite : { condition : Condition, rules : List Node } } → Node) →
Node
let example
: Node
= λ(Node : Type) →
λ(Leaf : { leaf : Field } → Node) →
λ(Branch : { composite : { condition : Condition, rules : List Node } } → Node) →
Branch
{ composite =
{ condition = Condition.And
, rules =
[ Branch
{ composite =
{ condition = Condition.And
, rules = [ Leaf { leaf = Field.S { exists = "hi" } } ]
}
}
, Branch
{ composite =
{ condition = Condition.Or
, rules = [ Leaf { leaf = Field.B { static = True } } ]
}
}
, Branch
{ composite =
{ condition = Condition.And
, rules =
[ Branch
{ composite =
{ condition = Condition.And
, rules =
[ Leaf { leaf = Field.S { exists = "hi" } } ]
}
}
, Branch
{ composite =
{ condition = Condition.Or
, rules =
[ Leaf { leaf = Field.B { static = True } } ]
}
}
]
}
}
]
}
}
in example
Here is the diff between the two:
12,13c12,13
< ∀(Leaf : { leaf : Field }) →
< ∀(Branch : { composite : { condition : Condition, rules : List Node } }) →
---
> ∀(Leaf : { leaf : Field } → Node) →
> ∀(Branch : { composite : { condition : Condition, rules : List Node } } → Node) →
18,20c18,20
< = ∀(Node : Type) →
< ∀(Leaf : { leaf : Field }) →
< ∀(Branch : { composite : { condition : Condition, rules : List Node } }) →
---
> = λ(Node : Type) →
> λ(Leaf : { leaf : Field } → Node) →
> λ(Branch : { composite : { condition : Condition, rules : List Node } } → Node) →
34c34
< , rules = [ Leaf { leaf = Field.S { static = true } } ]
---
> , rules = [ Leaf { leaf = Field.B { static = True } } ]
52c52
< [ Leaf { leaf = Field.S { static = true } } ]
---
> [ Leaf { leaf = Field.B { static = True } } ]