Language Compare F#, Ocaml, Scala, Clojure and Haskell

clojure-match.clj

(use '[clojure.core.match :only [match]])

(defn evaluate [env exp]
  (match [exp]
    [(['Number a] :seq)] a
    [(['Add x y] :seq)] (+ (evaluate env x) (evaluate env y))
    [(['Multiply x y] :seq)] (* (evaluate env x) (evaluate env y))
    [(['Variable i] :seq)] (env i)))
    
(def environment {"a" 3, "b" 4, "c" 5})

(def expression-tree '(Add (Variable "a") (Multiply (Number 2) (Variable "b"))))

(def result (evaluate environment expression-tree)) 

clojure-protocol.clj

(defprotocol Expression
  (evaluate [e env] ))
  
(deftype Number1 [x])
(deftype Add [x y] )
(deftype Multiply [x y])
(deftype Variable [x])

(extend-protocol Expression
  Number1  (evaluate [e env] (.x e ) )
  Add      (evaluate [e env] (+ (evaluate (.x e) env) (evaluate (.y e) env)))
  Multiply (evaluate [e env] (* (evaluate (.x e) env) (evaluate (.y e) env)))
  Variable (evaluate [e env] (env (.x e))))

(def environment {"a" 3, "b" 4, "c" 5})  

(def expression-tree (Add. (Variable. "a") (Multiply. (Number1. 2) (Variable. "b"))))

(def result (evaluate expression-tree environment)) 
  

fsharp.ml

//Here's some F# code...

type Expression = 
    | Number of int
    | Add of Expression * Expression
    | Multiply of Expression * Expression
    | Variable of string

let rec Evaluate (env:Map<string,int>) exp = 
    match exp with
    | Number n -> n
    | Add (x, y) -> Evaluate env x + Evaluate env y
    | Multiply (x, y) -> Evaluate env x * Evaluate env y
    | Variable id    -> env.[id]

let environment = Map.ofList [ "a", 1 ;
                               "b", 2 ;
                               "c", 3 ]

// Create an expression tree that represents
// the expression: a + 2 * b.
let expressionTree1 = Add(Variable "a", Multiply(Number 2, Variable "b"))

// Evaluate the expression a + 2 * b, given the
// table of values for the variables.
let result = Evaluate environment expressionTree1

haskell.hs

import Data.Map

data Expression = 
    Number   Int
  | Add      Expression Expression
  | Multiply Expression Expression
  | Variable String
  
evaluate :: Map String Int -> Expression -> Int
evaluate env (Number x) = x
evaluate env (Add x y) = evaluate env x + evaluate env y
evaluate env (Multiply x y) = evaluate env x * evaluate env y
evaluate env (Variable x) = findWithDefault 0 x env

environment = fromList([("a",3), ("b",4), ("c",7)])

expressionTree = Add (Variable "a") (Multiply (Number 2) (Variable "b"))

result = evaluate environment expressionTree

ocaml.ml

type expression = 
    Number of int
  | Add of expression * expression
  | Multiply of expression * expression
  | Variable of string
  
  
let rec evaluate (env: string->int) exp = 
  match exp with
      Number n -> n
    | Add (x, y) -> evaluate env x + evaluate env y
    | Multiply (x, y) -> evaluate env x * evaluate env y
    | Variable id    -> env id

let environment (str: string) : 'a = match str with "a" -> 3 | "b" -> 4 | "c" -> 5

let expressiontree1 = Add(Variable "a", Multiply(Number 2, Variable "b"))

let result = evaluate environment expressiontree1

scala.scala

abstract class Expression

case class Number(i: Int) extends Expression
case class Add(x: Expression, y: Expression) extends Expression
case class Multiply(x: Expression, y: Expression) extends Expression
case class Variable(id: Symbol) extends Expression

object Maths extends App {
  val environment = Map('a -> 1,
      'b -> 2,
      'c -> 3)
      
  def evaluate(env: Map[Symbol, Int], exp: Expression): Int = exp match {
    case Number(n: Int) => n    
    case Add(x, y) => evaluate(env, x) + evaluate(env, y)
    case Multiply(x, y) => evaluate(env, x) * evaluate(env, y)
    case Variable(id: Symbol) => env(id)
  }
      
  val expressionTree1 = Add(Variable('a), Multiply(Number(2), Variable('b)))
  
  println(evaluate(environment, expressionTree1))
}

ugly.java

import java.util.*;

public class Eval {
	
	public static Expression Number(final int x) {
		Expression exp = new Expression() {
			public int evaluate(Map env) { 
				return x; 
			}
		};
		return exp;
	}
	
	public static Expression Multiply(final Expression x, final Expression y) {
		Expression exp = new Expression() {
			public int evaluate(Map env) { 
				return x.evaluate(env) * y.evaluate(env); 
			}
		};
		return exp;
	}
	
	public static Expression Add(final Expression x, final Expression y) {
		Expression exp = new Expression() {
			public int evaluate(Map env) { 
				return x.evaluate(env) + y.evaluate(env); 
			}
		};
		return exp;
	}
	
	public static Expression Variable(final String var) {
		Expression exp = new Expression() {
			public int evaluate(Map env) { 
				return (Integer)env.get(var); 
			}
		};
		return exp;
	}
	
	public static void main(String[] args){
		Map env=new HashMap();
		env.put("a", 3);
		env.put("b", 4);
		env.put("c", 5);
		
		Expression expressionTree=Add(Variable("a"), Multiply(Number(2), Variable("b")));
		int result=expressionTree.evaluate(env);
		
		System.out.println(result);
	}

}

abstract class Expression {
	public abstract int evaluate(Map env);
}