evalute.ts

  public evaluate(variables: Array<expressionOperand>): expressionValue
  {
    if (this._expressionStack.length === 0) return false;

    if (variables.length != this._variables.length) return false;

    const len: number = variables.length;
    let j: number;
    for (j = 0; j < len; ++j) {
      if (!this.__isValidOperand(variables[j])) return false;
    }

    let token     = "";
    let tokenType = "";

    const opStack:Array<expressionOperand> = new Array<expressionOperand>();

    let arg1: expressionOperand;
    let arg2: expressionOperand;
    let i: number;
    let f: ExpressionFcn;

    i = 0;
    while (i < this._expressionStack.length)
    {
      // in reverse order, type is before value
      tokenType = this._expressionStack[i];
      token     = this._expressionStack[i+1];

      switch (tokenType)
      {
        case this.IS_NUMBER:
          opStack.push(+token);
          break;

        case this.IS_ONE_ARG_FUNCTION:
          arg1 = opStack.pop() as expressionOperand;

          f = (this as unknown as Record<string, ExpressionFcn>)[token] as ExpressionFcn;
          if (f === undefined) return false;     // unsupported function

          opStack.push( f(arg1) );
          break;

        case this.IS_TWO_ARG_FUNCTION:
          arg1 = opStack.pop() as expressionOperand;
          arg2 = opStack.pop() as expressionOperand;

          f = (this as unknown as Record<string, ExpressionFcn>)[token] as ExpressionFcn;
          if (f === undefined) return false;

          opStack.push( f(arg1, arg2) );
          break;

        case this.IS_VARIABLE:
          for (j = 0; j < len; ++j) {
            if( token === this._variables[j] ) opStack.push(variables[j]);
          }
          break;

        case this.IS_STR_LITERAL:
          opStack.push(token.toString());
          break;

        case this.IS_ARRAY:
          opStack.push(token.toString())
          break;

        default:
          return false;  // invalid token
      }

      i += 2;
    }

    return opStack[0];
  }