`sig
val to_string : OpamTypes.filter -> string
type env = OpamTypes.full_variable -> OpamTypes.variable_contents option
val contents_of_variable :
OpamFilter.env ->
OpamTypes.full_variable -> OpamTypes.variable_contents option
val contents_of_variable_exn :
OpamFilter.env -> OpamTypes.full_variable -> OpamTypes.variable_contents
val substitute_string : OpamFilter.env -> string -> string
val substitute_file : OpamFilter.env -> OpamTypes.basename -> unit
val eval : OpamFilter.env -> OpamTypes.filter -> bool
val eval_opt : OpamFilter.env -> OpamTypes.filter option -> bool
val commands : OpamFilter.env -> OpamTypes.command list -> string list list
end`