Program modifications at low cost?

The expectation that program modifications at low cost ought to be possible is one that calls for closer analysis. First it should be noted that such an expectation cannot be supported by analogy with modifications of other complicated man-made constructions. Where modifications are occasionally put into action, for example in the case of buildings, they are well known to be expensive and in fact complete demolition of the existing building followed by new construction is often found to be preferable economically. Second, the expectation of the possibility of low cost program modifications conceivably finds support in the fact that a program is a text held in a medium allowing for easy editing. For this support to be valid it must clearly be assumed that the dominating cost is one of text manipulation. This would agree with a notion of programming as text production. On the Theory Building View this whole argument is false. This view gives no support to an expectation that program modifications at low cost are generally possible.

 — Peter Naur, Programming as Theory Building”