Hi,
Thanks Jeremy, that's quite ingenious. However, I've hit a problem in the
definition of the constructor functions (the full code + compiler error
is below). Now, I know that nonlink_node_t is a subset of super_node_t,
and therefore any variant valid for nonlink_node_t is also acceptable for
super_node_t. But how do I tell this to the compiler? (Note that having
users of the module manually casting types with :> is something I would
rather avoid).
Thanks again,
Dario
module rec Node:
sig
type nonlink_node_t = [ `Text of string | `Bold of Node.super_node_t
list ]
type link_node_t = [ `See of string | `Mref of string * nonlink_node_t
list ]
type super_node_t = [ nonlink_node_t | link_node_t ]
val text: string -> nonlink_node_t
val bold: super_node_t list -> nonlink_node_t
val see: string -> link_node_t
val mref: string -> nonlink_node_t list -> link_node_t
end =
struct
type nonlink_node_t = [ `Text of string | `Bold of Node.super_node_t
list ]
type link_node_t = [ `See of string | `Mref of string * nonlink_node_t
list ]
type super_node_t = [ nonlink_node_t | link_node_t ]
let text txt = `Text txt
let bold seq = `Bold seq
let see ref = `See ref
let mref ref seq = `Mref (ref, seq)
end
open Node
let foo = text "foo"
let bar = bold [text "bar"]
Error: This expression has type Node.nonlink_node_t
but is here used with type Node.super_node_t
The first variant type does not allow tag(s) `Mref, `See
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