I want to have a Map datastructure for "env" in my lisp interpreter.
My code in env.mli is
module Env = Map.Make(String)
type t = (Ast.expression) Env.t
val empty: t
val add: string -> Ast.expression -> t -> t
val lookup: string -> t -> Ast.expression
But my code in env.ml is:
module Env = Map.Make(String)
type t = (Ast.expression) Env.t
let (empty: t) = Env.empty
let add (id: string) (value: Ast.expression) (env: t): t = Env.add id (value) env
let lookup (id: string) (env: t) : Ast.expression = Env.find id env
And there aren’t any error prompt. Curious about why and how to modify my code.
Quite new to functors and maybe I didn’t fully understand it.
Thank you.
>Solution :
Based on the little information you provide, my guess is that what you want is to expose the Env fully as a map over strings. If so, you should replace
module Env = Map.Make(String)
with
module Env : Map.S with type key = string
but you could also leave the key type abstract:
module Env : Map.S
or expose only the type of the map:
module Env : sig
type 'a env
type t = e env
...
end = struct
module Env = Map.Make(String)
type 'a env = 'a Env.t
type t = Ast.expression Env.t
...
end
or you could make t itself abstract, to avoid referencing the env/map type at all:
module Env : sig
type t
...
end = struct
module Env = Map.Make(String)
type t = Ast.expression Env.t
...
end
There’s many possible solutions depending on what you actually need.