Language Comparison: Simple AST in Clojure, F#, Ocaml, Scala, Clojure, Ruby, C++, C#, Go, Haskell and others

clojure-match.clj

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

(defn evaluate [env [sym x y]]
  (match [sym]
    ['Number]   x
    ['Add]      (+ (evaluate env x) (evaluate env y))
    ['Multiply] (* (evaluate env x) (evaluate env y))
    ['Variable] (env x)))
    
(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)) 
  

cpp.cpp

#include <string>
#include <iostream>
#include <map>
#include <memory>

typedef std::map <std::string, int> Variables;

struct Expr
{
    virtual ~Expr() {}
    virtual int eval (Variables&) = 0;
};

struct Multiply   : public Expr
{
    std::unique_ptr<Expr> e1, e2;

    Multiply (Expr* lhs, Expr* rhs)  : e1 (lhs), e2 (rhs) {}
    int eval (Variables& env)     { return e1->eval (env) * e2->eval (env); }
};

struct Add   : public Expr
{
    std::unique_ptr<Expr> e1, e2;

    Add (Expr* lhs, Expr* rhs)  : e1 (lhs), e2 (rhs) {}
    int eval (Variables& env)     { return e1->eval (env) + e2->eval (env); }
};

struct Constant   : public Expr
{
    int value;

    Constant (int val)  : value (val) {}
    int eval (Variables&)         { return value; }
};

struct Variable   : public Expr
{
    std::string varName;

    Variable (const std::string& name)  : varName (name) {}
    int eval (Variables& env)     { return env [varName]; }
};

int main (int argc, char** argv)
{
    Variables env;
    env["a"] = 3;
    env["b"] = 4;
    env["c"] = 5;

    Add tree (new Variable ("a"),
              new Multiply (new Constant (2),
                            new Variable ("b")));

    std::cout << tree.eval (env) << std::endl;
}

csharp.cs

using System;
using Env = System.Collections.Generic.Dictionary<string, int>;

delegate int Expr(Env e);

public class Program
{
    public static void Main()
    {
        Func<string, Expr> Var = s => env => env[s];
        Func<int, Expr> Num = i => env => i;
        Func<Expr, Expr, Expr> Add = (x, y) => env => x(env) + y(env);
        Func<Expr, Expr, Expr> Mul = (x, y) => env => x(env) * y(env);

        var expr = Add(Var("a"), Mul(Num(2), Var("b")));

        Console.WriteLine(expr(new Env { { "a", 3 }, { "b", 4 }, { "c", 5 } }));
    }
}

fsharp.fs

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 ]

let expressionTree1 = Add(Variable "a", Multiply(Number 2, Variable "b"))

let result = Evaluate environment expressionTree1

go-type-matching.go

package main
import "fmt"

type Add struct{a, b interface{}}
type Mul struct{a, b interface{}}

func eval(env map[string]int, e interface{}) int {
    switch v := e.(type) {
        case int: return v
        case string: return env[v]
        case Add: return eval(env, v.a) + eval(env, v.b)
        case Mul: return eval(env, v.a) * eval(env, v.b)
    }
    return 0
}

func main() {
    env := map[string]int{"a":3, "b":4, "c":5}
    ast := Add{"a", Mul{2, "b"}}
    fmt.Println(eval(env, ast))
}

haskell-case.hs

import Data.Map

data Expression = 
    Number   Int
  | Add      Expression Expression
  | Multiply Expression Expression
  | Variable String
  
evaluate :: Map String Int -> Expression -> Int
evaluate env exp = 
  case exp of
    Number x     -> x
    Add x y      -> evaluate env x + evaluate env y
    Multiply x y -> evaluate env x * evaluate env y
    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

haskell-constructor.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

nemerle.n

#pragma indent 
using Nemerle.Extensions;
using System.Collections.Generic;

variant Ast
  | Number   { val : int }
  | Add      { left : Ast; right : Ast }
  | Multiply { left : Ast; right : Ast }
  | Variable { name : string }

def eval(env, expr)
  match(expr)
    | Ast.Number(val) => val
    | Add(l, r)       => eval(env, l) + eval(env, r)    
    | Multiply(l, r)  => eval(env, l) * eval(env, r)
    | Variable(name)  => env[name]

def environment = Dictionary() <- ["a" = 3, "b" = 4, "c" = 5];
def expr = Ast.Add(Ast.Variable("a"), Ast.Multiply(Ast.Number(2), Ast.Variable("b")));    
def result = eval(environment, expr);

ocaml.ml

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

let rec evaluate env = function
  | 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 = function "a" -> 3 | "b" -> 4 | "c" -> 5

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

let result = evaluate environment expressiontree1

python.py

Number = lambda env, n: n
Add = lambda env, a, b: evaluate(env, a) + evaluate(env, b)
Multiply = lambda env, a, b: evaluate(env, a) * evaluate(env, b)
Variable = lambda env, x: env[x]

evaluate = lambda env, expr: expr[0](env, *expr[1:])

expression_tree = (Add, (Variable, 'a'),
                        (Multiply, (Number, 2),
                                   (Variable, 'b')))
environment = {'a': 3, 'b': 4, 'c': 5}

print evaluate(environment, expression_tree)

ruby-jimweirich.rb

def evaluate(env, exp)
  keyword, a, b = exp
  case keyword
  when :number;   a
  when :variable; env[a]
  when :add;      evaluate(env, a) + evaluate(env, b)
  when :multiply; evaluate(env, a) * evaluate(env, b)
  end
end

ExpressionTree = [:add, [:variable, :a], [:multiply, [:number, 2], [:variable, :b]]]
Env = { a: 3, b: 4, c: 5 }

puts evaluate(Env, ExpressionTree)

ruby2-jimweirich.rb

Number   = lambda { |env, num| num }
Variable = lambda { |env, var| env[var] }
Add      = lambda { |env, a, b| evaluate(env, a) + evaluate(env, b) }
Multiply = lambda { |env, a, b| evaluate(env, a) * evaluate(env, b) }

def evaluate(env, exp)
  op, *args = exp
  op.(env, *args)
end

ExpressionTree = [Add, [Variable, :a], [Multiply, [Number, 2], [Variable, :b]]]
Env = { a: 3, b: 4, c: 5 }

puts evaluate(Env, ExpressionTree)

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 {
	static int evaluate(Map env, Expression exp){ 
		if(exp instanceof Variable){  return (Integer)env.get(((Variable)exp).x); }
		else if(exp instanceof Number){ return ((Number)exp).x; }
		else if(exp instanceof Multiply){ return evaluate(env, ((Multiply)exp).x)*evaluate(env, ((Multiply)exp).y); }
		else if(exp instanceof Add){ return evaluate(env, ((Add)exp).x)+evaluate(env, ((Add)exp).y); }
		return 0;
	}
		
	public static void main(String[] args){
		Map env=new HashMap();
		env.put("a", 3);
		env.put("b", 4);
		env.put("c", 5);
		
		Expression expressionTree=new Add(new Variable("a"), new Multiply(new Number(2), new Variable("b")));
		System.out.println(evaluate(env, expressionTree));
	}
}
abstract class Expression {}

class Number extends Expression{ 
	int x; 
	Number(int x){ this.x=x; }
}

class Add extends Expression{ 
	Expression x; Expression y;
	Add(Expression x, Expression y){ this.x=x;  this.y=y; }
}

class Multiply extends Add{ 
	Multiply(Expression x, Expression y){ super(x, y); }
}

class Variable extends Expression{ 
	String x;
	Variable(String x){ this.x=x; }
}