The quote actually does not appear in Concepts, Techniques, and Models of Computer Programming but is Bernstein's summary of the work. Although it is an appropriate summary, it can easily be taken out of context. Van Roy and Haridi, authors of CTMCP, were mainly concerned with the trade-offs of programming paradigms. They observed that functional languages, like Haskell, and object-oriented/shared-state-concurrency languages, like Java, sit at opposite ends of a continuum. The functional paradigm is very easy to formally reason with, but can be very kludgy when expressing certain real world concepts, like state. The OO paradigm and the shared-state concurrency paradigm, on the other hand, are very powerful and expressive, but can be quite a pain to reason over. Van Roy and Haridi believed that programmers, rather than having to make a boolean decision between the two, should be allowed to work anywhere on the continuum, and they designed the Oz programming language to make that easy to do.
CTMCP is the bible for Oz. But it's more than just a language reference book. It is an exploration of this trade-off between language expressiveness and ease of comprehension. CTMCP outlines how programming concepts can be layered to form gradual steps between functional and OO languages by controlling the use of mutable state. The Oz language like Haskell, starts in a functional paradigm and makes the use of state explicit, but unlike Haskell it also tries to make the use of state easy and intuitive, rather than overly verbose. CTMCP advocates an avoidance of using a single paradigm to solve all problems.
Oz also has concurrency built in natively, and one of the overarching themes of CTMCP is that the use of concurrency greatly benefits from an understanding of this trade-off between expressiveness and ease of comprehension. Concurrency doesn't have to be difficult, and in the case of functional languages (think dataflow concurrency, as seen in Unix pipes) can be quite easy to use and comprehend. CTMCP posits that as one moves from functional to OO, concurrency analogously becomes both more expressive and more difficult to formally reason over. The use of concurrency therefore can become more tractable when programmers are made more aware of these trade-offs.
CTMCP is the bible for Oz. But it's more than just a language reference book. It is an exploration of this trade-off between language expressiveness and ease of comprehension. CTMCP outlines how programming concepts can be layered to form gradual steps between functional and OO languages by controlling the use of mutable state. The Oz language like Haskell, starts in a functional paradigm and makes the use of state explicit, but unlike Haskell it also tries to make the use of state easy and intuitive, rather than overly verbose. CTMCP advocates an avoidance of using a single paradigm to solve all problems.
Oz also has concurrency built in natively, and one of the overarching themes of CTMCP is that the use of concurrency greatly benefits from an understanding of this trade-off between expressiveness and ease of comprehension. Concurrency doesn't have to be difficult, and in the case of functional languages (think dataflow concurrency, as seen in Unix pipes) can be quite easy to use and comprehend. CTMCP posits that as one moves from functional to OO, concurrency analogously becomes both more expressive and more difficult to formally reason over. The use of concurrency therefore can become more tractable when programmers are made more aware of these trade-offs.
(CTMCP actually goes further and classifies the programming paradigms into an elaborate branching hierarchy, as can be seen here http://www.info.ucl.ac.be/~pvr/paradigmsDIAGRAMeng108.pdf)