Meta Dlang

metadlang.d

import std.stdio, std.format;

interface MetaDlangObject {
  const enum string eval();
}

interface MetaDlangExpr : MetaDlangObject {
}

interface MetaDlangStatement : MetaDlangObject {
}

class MetaDlangVariable : MetaDlangExpr {
  const string var_name;

  this(const string var_name) {
    this.var_name = var_name;
  }

  const enum string eval() {
    return this.var_name;
  }
}

abstract class MetaDlangBinaryExpr(string op) : MetaDlangExpr {
  const MetaDlangExpr lhs, rhs;

  this(const MetaDlangExpr lhs, const MetaDlangExpr rhs) {
    this.lhs = lhs;
    this.rhs = rhs;
  }

  const enum string eval() {
    return "%s %s %s".format(this.lhs.eval(), op, this.rhs.eval());
  }
}

class MetaDlangAdd : MetaDlangBinaryExpr!"+" {
  this(const MetaDlangExpr lhs, const MetaDlangExpr rhs) {
    super(lhs, rhs);
  }
}

class MetaDlangAssignExpr : MetaDlangBinaryExpr!"=" {
  this(const MetaDlangExpr lhs, const MetaDlangExpr rhs) {
    super(lhs, rhs);
  }
}

class MetaDlangExprToStatement : MetaDlangStatement {
  const MetaDlangExpr expr;
  this(const MetaDlangExpr expr) {
    this.expr = expr;
  }

  const enum string eval() {
    return "%s;".format(this.expr.eval());
  }
}

void main() {
  int a = 1, b = 2, c;

  static const MetaDlangExpr var_a = new MetaDlangVariable("a");
  static const MetaDlangExpr var_b = new MetaDlangVariable("b");
  static const MetaDlangExpr var_c = new MetaDlangVariable("c");
  static const MetaDlangExpr add_expr = new MetaDlangAdd(var_a, var_b);
  static const MetaDlangExpr assign_expr_to_c = new MetaDlangAssignExpr(var_c, add_expr);
  static const MetaDlangStatement assign_statement = new MetaDlangExprToStatement(assign_expr_to_c);

  mixin(assign_statement.eval);

  writeln("a: ", a);
  writeln("b: ", b);
  writeln("c: ", c);
}