ML-like languages are great for creating interpreters or compilers, by virtue of Algebraic Data Types. Haxe's enum allow for writing similarly elegant code.
Below is the Haxe version of F# code for a simple expression interpreter, described in Programming Language Concepts (Sestoft).
Implementation
The eval function uses pattern matching against an expression, represented by a parametized enum data data type.
class Main { /** The eval function uses pattern matching against an expression, represented by a parametized enum data data type. **/ static public function eval(e:Expr):Int { return switch e { case CstI(x): x; case Prim("+", e1, e2): eval(e1) + eval(e2) ; case Prim("-", e1, e2): eval(e1) - eval(e2) ; case Prim("*", e1, e2): eval(e1) * eval(e2) ; case Prim(_) : throw "Unknown primitive"; } } // Some simple tests. static public function main():Void { // Evaluate the expression 23. trace( eval( CstI(23) ) ); // Evaluate the expression (7 * 9) + 10. trace( eval( Prim("+", Prim("*", CstI(7), CstI(9)), CstI(10)) ) ); } } /* Algabreic Data Type for an arithmetic expression. In F# would be: type expr = | CstI of int | Prim of string * exp * exp */ enum Expr { CstI( x:Int ); // An integer constant Prim( op:String, e1:Expr, e2:Expr ); // Or a primary arithmetic expression }
