Arguments about the relative merits of different languages can get very heated and are often extremely subjective. However, just as there are some objectively testable advantages to Pop-11 there are also some disadvantages:
(a) It is not available on PCs, except on relatively powerful PCs running the Linux operating system (a version of Unix). A port of Poplog to Windows NT port has been started but by January 1996 had not been completed. (For up to date information, please contact Integral Solutions Ltd., address above.) The is a Mac implementation of of Pop-11, known as Alphapop, previously available from Cognitive Applications Ltd, does not run under recent versions of the Mac operating system.
(b) Because of its size and the supported machine types, Pop-11 is not recommended for small embedded systems. However, it can be used to implement cross compilers for embedded systems.
(c) The complex, user-extendable, syntax makes it extremely difficult to automate the analysis of Pop-11 programs. For applications where mathematical analysis of software is a requirement, e.g. flight control systems, Pop-11, would not be suitable, though it could be used for rapidly developing prototypes prior to final implementation, and it could support expert-systems acting alongside the critical software, e.g. to analyse data or make heuristic suggestions that would not be adopted unless checked by a more rigorous system, or a person.
(d) Because of the long history of its development and our inability in the early days (e.g. 1970s and early 1980s) to anticipate some of the extensions that would be required several years later, there were some unfortunate choices of identifer names that are hard to repair without annoying existing users, and several aspects of the syntax of Pop-11 that are messy. Up to Poplog version 15, the default for procedure formal parameters and output variables was, unfortunately, to declare them as "vars" not "lvars" (lexical variables). This has now been remedied, though a special compile_mode is available to restore earlier semantics.
(e) The undisciplined use of the open stack in Pop-11 can lead to obscure run-time errors, even though it is often very useful.
(f) Some users find the redundant syntax of Pop-11 too verbose, especially users with a strong mathematical bent, many of whom prefer the elegance and economy of Lisp, supported by a powerful editor.
(g) The language is not very widely used, though there are pockets of enthusiasm in various countries, both among academics and among commercial users, and the main distributor, Integral Solutions Ltd has managed to continue growing despite the very severe recession in recent years.
(h) Like Common Lisp, Pop-11 is a very rich and complex language. Becoming fluent in the use of all of its capabilities can take a long time (e.g. a year or more), though many of its users have found the learning well worth while.
(i) Because Pop-11 has so many features it is possible for beginners inadvertently to trip over more advanced features and then be mystified and discouraged. This can be a disadvantage, though in a good teaching environment it is also a source of important new learning.
(j) Because Pop-11 is compiled (for speed) rather than interpreted, it is not possible to produce such sophisticated run-time debugging tools as for those versions of Lisp that have an interpreter. However, this disadvantage has recently been reduced considerably by the development of new source-level debugging tools, by Simon Nichols and Robert Duncan, documented in the online HELP DEBUGGER file.