substitute.js

import { Instruction, IOP1, IOP2, IOP3, IVAR, IEXPR, ternaryInstruction, binaryInstruction, unaryInstruction } from './instruction';

export default function substitute(tokens, variable, expr) {
  var newexpression = [];
  for (var i = 0; i < tokens.length; i++) {
    var item = tokens[i];
    var type = item.type;
    if (type === IVAR && item.value === variable) {
      for (var j = 0; j < expr.tokens.length; j++) {
        var expritem = expr.tokens[j];
        var replitem;
        if (expritem.type === IOP1) {
          replitem = unaryInstruction(expritem.value);
        } else if (expritem.type === IOP2) {
          replitem = binaryInstruction(expritem.value);
        } else if (expritem.type === IOP3) {
          replitem = ternaryInstruction(expritem.value);
        } else {
          replitem = new Instruction(expritem.type, expritem.value);
        }
        newexpression.push(replitem);
      }
    } else if (type === IEXPR) {
      newexpression.push(new Instruction(IEXPR, substitute(item.value, variable, expr)));
    } else {
      newexpression.push(item);
    }
  }
  return newexpression;
}