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Yes, thank you, your code example is much better than mine. The simplifying potential of expression-oriented languages is huge. Alan Perlis said[0]: "symmetry

Yes, thank you, your code example is much better than mine. The simplifying potential of expression-oriented languages is huge. Alan Perlis said[0]: "symmetry is a complexity-reducing concept; seek it everywhere", and this is a great example of that. For example, languages like C and Ada have both if statements and if expressions, this is a duplication that can be eliminated by making them expression-oriented so you only have an if expression like in Haskell or ML. But, interestingly, there is one historical case of a language going from expression-oriented to statement/expression separation: ALGOL-W[1] was expression oriented, Pascal[2], its successor, separates statements from expressions. Wirth designed both. I don't know what the motivation was, but I suspect it's because Pascal was designed to be an educational language, and Wirth must have thought that separating expressions and statements made didactic sense when teaching programming as a recipe or list of things to do, as opposed to the more mathematized formulation of expression-oriented languages (of having an evaluation function from expressions to values). The successors of Pascal (Ada, Modula and its sequels) retain the statement/expression separation. [0]: http://pu.inf.uni-tuebingen.de/users/klaeren/epigrams.html http://pu.inf.uni-tuebingen.de/users/klaeren/epigrams.html [1]: https://en.wikipedia.org/wiki/ALGOL_W https://en.wikipedia.org/wiki/ALGOL_W [2]: https://en.wikipedia.org/wiki/Pascal_(programming_language) https://en.wikipedia.org/wiki/Pascal_(programming_language)

tangus 5y ago
I can't say for sure, but I suspect it was a reaction to ALGOL-68. Creators of later Algolish languages usually made a point of rejecting features of Algol-68 they saw as prone to abuse. And the block expressions in Algol-68 were certainly used and abused. Basically, the type and value of a block (BEGIN ... END or ( ... )) are those of its last expression, so you can put them anywhere. For example, Algol-68 has the looping construct WHILE <condition> DO <body> OD, but not C's `do <body> while (<condition>)`. So what do you do if you want to have the test at the end of the loop body? Simply WHILE ( <body>; <condition> ) DO SKIP OD I guess you'd get used to those idioms eventually, or some coding conventions would have arisen if the language had been successful. But I can understand language creators looking at that and seeing how getting rid of it simplifies not only their compilers but also the programs written in their languages.
- Wildgoose 5y ago
  What is wrong with simply: test := True; WHILE test DO <body>; test = <condition> OD
  - chalst 5y ago
    That introduces a variable that has to be initialised outside the control block. It's not terrible as hacks go, but I guess the readability cost of the additional variable is higher than having the body in the condition.
    - Wildgoose 5y ago
      Agreed, but it also allows for a more sophisticated <condition> testing to take place within the body of the loop.
    - tejtm 5y ago
      standard practice "Sentinel value" when I was a student
  - tangus 5y ago
    Nothing is wrong with it, but your suggestion comes 40 years too late. The popular idiom was the one I mentioned.

tangus 5y ago

I can't say for sure, but I suspect it was a reaction to ALGOL-68. Creators of later Algolish languages usually made a point of rejecting features of Algol-68 they saw as prone to abuse. And the block expressions in Algol-68 were certainly used and abused. Basically, the type and value of a block (BEGIN ... END or ( ... )) are those of its last expression, so you can put them anywhere. For example, Algol-68 has the looping construct WHILE <condition> DO <body> OD, but not C's `do <body> while (<condition>)`. So what do you do if you want to have the test at the end of the loop body? Simply WHILE ( <body>; <condition> ) DO SKIP OD I guess you'd get used to those idioms eventually, or some coding conventions would have arisen if the language had been successful. But I can understand language creators looking at that and seeing how getting rid of it simplifies not only their compilers but also the programs written in their languages.

Wildgoose 5y ago
What is wrong with simply: test := True; WHILE test DO <body>; test = <condition> OD
- chalst 5y ago
  That introduces a variable that has to be initialised outside the control block. It's not terrible as hacks go, but I guess the readability cost of the additional variable is higher than having the body in the condition.
  - Wildgoose 5y ago
    Agreed, but it also allows for a more sophisticated <condition> testing to take place within the body of the loop.
  - tejtm 5y ago
    standard practice "Sentinel value" when I was a student
- tangus 5y ago
  Nothing is wrong with it, but your suggestion comes 40 years too late. The popular idiom was the one I mentioned.