Letters between Backus and Dijkstra (1979)
I&#x27;m sad that in this thread and <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11786193" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=11786193</a>, nobody is actually talking about the technical arguments at play. I&#x27;ve only read the EWD692 &quot;opening salvo&quot; but already there are interesting things to point out.<p>EWD1303:<p>&gt; The profound significance of Dekker&#x27;s solution of 1959, however, was that it showed the role that mathematical proof could play in the process of program design. Now, more than 40 years later, this role is still hardly recognized in the world of discrete designs. If mathematics is allowed to play a role at all, it is in the form of a posteriori verification, i.e. by showing by usually mechanized mathematics that the design meets its specifications; the strong guidance that correctness concerns can provide to the design process is rarely exploited. On the whole it is still &quot;Code first, debug later&quot; instead of &quot;Think first, code later&quot;, which is a pity, but Computing Science cannot complain: we are free to speak, we don&#x27;t have a right to be heard. And in later years Computing Science has spoken: in connection with the calculational derivation of programs —and then of mathematical proofs in general— the names of R.W. Floyd, C.A.R. Hoare, D. Gries, C.C. Morgan, A.J.M. van Gasteren and W.H.J. Feijen are the first to come to my mind.<p>Backus as quoted in EWD692 (Djikstra attacks this):<p>&gt; One advantage of this algebra over other proof techniques is that the programmer can use his programming language as the language for deriving proofs, rather than having to state proofs in a separate logical system that merely [sic!] talks about his programs.<p>From a perspective of a PL person like myself, these ideals are very compatible. Without correctness by construction, there is not enough proof reuse so formality will forever be doomed for niche applications (aka computers embedded in dangerous things). Likewise after trying out intuitionistic type theory--based things (e.g. Agda) separating the program and proof langauges just seems clumsy. Overall separating programming and proof whether spatially (seperate languages) or temporally (correctness proved after the fact) is bad, and the reasons hardly depend on the dimension of separation