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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 binary operator. *)
     14   | Binary of char * expr * expr
     15 
     16   (* variant for function calls. *)
     17   | Call of string * expr array
     18 
     19 (* proto - This type represents the "prototype" for a function, which captures
     20  * its name, and its argument names (thus implicitly the number of arguments the
     21  * function takes). *)
     22 type proto = Prototype of string * string array
     23 
     24 (* func - This type represents a function definition itself. *)
     25 type func = Function of proto * expr
     26