Nsryjdtyk

I'm working on an interpreter assignment in OCaml in which I have to bind values. For example I might want to bind the value "A" to the value 3.

I'm trying to use the hash table module in ocaml to accomplishments for easy storage and lookups but there seem to be multiple problems related to scoping, and return types.

What I want to do is when the case in which the second value popped off the stack is of type name I want to bind NAME to whatever the first value popped was and then append UNIT to the stack. Unfortunately for some reason my solution doesn't work. Can anyone help me?

open Hashtbl;;



let bound_values = Hashtbl.create 123456        

type stackVal =    

INT of int    

| STR of string    

| BOOL of bool    

| NAME of string    

| UNIT of unit    

| ERROR        



let callBind (stk : stackVal list) : stackVal list =    

match (stk) with    

x::NAME(y)::stk -> UNIT(Hashtbl.add bound_values y x)::stk    

| _ -> ERROR::stk

You need to define the type stackVal before defining your hash table. Otherwise the type technically resides in an inner scope. Another way of saying it is that you are expecting the table to contain values of a type that didn't exist when the table was created.

Here are two small examples showing the effect of the two orders:

$ ocaml

        OCaml version 4.06.1



# let ht = Hashtbl.create 1;;

val ht : ('_weak1, '_weak2) Hashtbl.t = <abstr>

# type t = A | B;;

type t = A | B

# let () = Hashtbl.add ht "key" A;;

Error: This expression has type t but an expression

was expected of type 'a

The type constructor t would escape its scope

#



$ ocaml

        OCaml version 4.06.1



# type t = A | B;;

type t = A | B

# let ht = Hashtbl.create 1;;

val ht : ('_weak1, '_weak2) Hashtbl.t = <abstr>

# let () = Hashtbl.add ht "key" A;;

# Hashtbl.find ht "key";;

- : t = A

#

As a side note, I would not open the Hashtbl module. Your code already uses full names (Hashtbl.x), so there's no benefit in opening it. And it's best to open as few modules as possible.