sch2.go

package main

import "fmt"

type Environment struct {
    bindings map[string] SExp
}

func (e Environment) Lookup(name string) SExp {
   var result SExp;
   value,success := e.bindings[name];
   if (!success) {
      fmt.Printf("1...");
      result = SExpSymbol("<NULL>")
   } else {
      fmt.Printf("2...");
      result = value
   }
   return result
}

func (e Environment) Bind(name string,value SExp)  {
    e.bindings[name] = value;
}

type  SExp interface {
   Evaluate(e Environment) SExp;
   Apply(args SExpList ) (result SExp,success bool);
   AsString() string;   
}

type SExpNumber int
type SExpString string
type SExpSymbol string
type SExpList []SExp
type SExpFunc func(l SExpList) SExp

/// Number

func (this SExpNumber) Evaluate(e Environment) SExp {
   return this;
}

func (this SExpNumber) Apply(args SExpList) (result SExp,success bool) {
   success = false;
   return
}

func (this SExpNumber) AsString() string {
   return fmt.Sprintf("%d",this);
}

/// String

func (this SExpString) Evaluate(e Environment) SExp {
   return this;
}
func (this SExpString) Apply(args SExpList) (result SExp,success bool) {
   success = false;
   return
}

func (this SExpString) AsString() string {
   return fmt.Sprintf("\"%s\"",this);
}

/// Symbol

func (this SExpSymbol) Evaluate(e Environment) SExp {
   return e.Lookup(string(this));
}

func (this SExpSymbol) AsString() string {
   return fmt.Sprintf("%s",this);
}

func (this SExpSymbol) Apply(args SExpList) (result SExp,success bool) {  
   success = false;
   return
}

/// List

func (this SExpList) Evaluate(env Environment) SExp {
   f := this[0].Evaluate(env);
   args := make( []SExp, len(this) - 1);
   for i,e := range(this) {
      if (i > 0) {
         args[i-1] = e.Evaluate(env);
      }
   }
   fmt.Printf("1!!!\n");
   result,_ := f.Apply(args);
   return result
}

func (this SExpList) Apply(args SExpList) (result SExp,success bool) {  
   success = false;
   return
}

func (this SExpList) AsString() string {
   var result string;
   result = "(";
   for _,e := range(this) {
      result = result + e.AsString()  + " "
   }
   result = result + ")";
   return result
}

/// SExp Func

func (this SExpFunc) Evaluate(e Environment) SExp {
   return this
}

func (this SExpFunc) AsString() string {
   return "<func>"
}

func (this SExpFunc) Apply(args SExpList) (result SExp,success bool) {  
   success = true;
   result = this(args);
   return
}



func main() {
    x := new(int);
    fmt.Printf("%d\n",*x);
    *x = 2;
    fmt.Printf("%d\n",*x);
    var v SExp;
    v = SExpNumber(4);
    fmt.Printf("%d\n",v);
   
    env := Environment {make(map[string] SExp)};
    env.Bind("+", 
             SExpFunc(func (args []SExp) SExp{ 
               fmt.Printf("2!!!\n");
                return SExpNumber(int(args[0].(SExpNumber)) +
                                  int(args[1].(SExpNumber)))}));

    list1 := SExpList(
                []SExp {SExpNumber(2),
                        SExpNumber(3),
                        SExpString("A"),
                        SExpNumber(5),
                        SExpString("dsf")});

    fmt.Printf("1 --> %s\n",list1.AsString());

    exp1 := SExpList(
                []SExp {SExpSymbol("+"),
                        SExpList(
                              []SExp {SExpSymbol("+"),
                                      SExpNumber(4),
                                      SExpNumber(3)}),
                        SExpNumber(2)});
                        
    
    fmt.Printf("2 --> %s\n",(exp1.Evaluate(env)).AsString())
}