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      1 (*===----------------------------------------------------------------------===
      2  * Abstract Syntax Tree (aka Parse Tree)
      3  *===----------------------------------------------------------------------===*)
      4 
      5 (* expr - Base type for all expression nodes. *)
      6 type expr =
      7   (* variant for numeric literals like "1.0". *)
      8   | Number of float
      9 
     10   (* variant for referencing a variable, like "a". *)
     11   | Variable of string
     12 
     13   (* variant for a unary operator. *)
     14   | Unary of char * expr
     15 
     16   (* variant for a binary operator. *)
     17   | Binary of char * expr * expr
     18 
     19   (* variant for function calls. *)
     20   | Call of string * expr array
     21 
     22   (* variant for if/then/else. *)
     23   | If of expr * expr * expr
     24 
     25   (* variant for for/in. *)
     26   | For of string * expr * expr * expr option * expr
     27 
     28   (* variant for var/in. *)
     29   | Var of (string * expr option) array * expr
     30 
     31 (* proto - This type represents the "prototype" for a function, which captures
     32  * its name, and its argument names (thus implicitly the number of arguments the
     33  * function takes). *)
     34 type proto =
     35   | Prototype of string * string array
     36   | BinOpPrototype of string * string array * int
     37 
     38 (* func - This type represents a function definition itself. *)
     39 type func = Function of proto * expr
     40