4 ms·

On a blackboard it didn't matter whether all the parentheses matched all the time

by jepler 4y ago

metroholografix 4y ago
What matters on the blackboard (or a book) is "understanding" and that is not affected by a missing paren or two (which is a testament to Lisp's regularity of syntax). When they wanted their programs executed by a computer, their editor -Edwin- matched parens, exactly like how one would do it today, or even easier with things like Paredit.
- wrycoder 4y ago
  And if you leave out a paren, the resulting auto-indented structure will look obviously wrong, signalling that you made an error. It's not so obvious in Python when you make an indentation error in a complicated if/elif/else structure.
  - kazinator 4y ago
    In a language with a sane syntax, we can do this: if (A) { if (A) { B B C --> C } D D E E } Imagine that is 300 lines long and BCDE contain their own nesting and such. We can do a "git diff -w" and just see that the closing brace moved and that there are no changes in D and E. Do the same in Python and "git diff -w" comes up empty.
teddyh 4y ago
I’ve watched those videos. IIRC, the parentheses always matched.
wrycoder 4y ago
It's not the parentheses or the Polish notation that matter. Those are covered in the first chapter of any Lisp/Scheme book and they are trivial, especially with a proper editor that understands structure and will indent unambiguously accordingly. Unless you're stuck on simple editors like Notepad or Nano, there's no issue here. What's more challenging in Scheme, as Abelson and Sussman teach it, is the use of recursion instead of looping and in particular understanding that recursion is only equivalent to looping when the recursion is in "tail position", i.e. when there is nothing left for the calling function to do except return to its own caller. Common Lisp style tends to use looping, not recursion.

On a blackboard it didn't matter whether all the parentheses matched all the time

by jepler 4y ago

On a blackboard it didn't matter whether all the parentheses matched all the time

What matters on the blackboard (or a book) is "understanding" and that is not affected by a missing paren or two (which is a testament to Lisp's regularity of syntax). When they wanted their programs executed by a computer, their editor -Edwin- matched parens, exactly like how one would do it today, or even easier with things like Paredit.

wrycoder 4y ago
And if you leave out a paren, the resulting auto-indented structure will look obviously wrong, signalling that you made an error. It's not so obvious in Python when you make an indentation error in a complicated if/elif/else structure.
- kazinator 4y ago
  In a language with a sane syntax, we can do this: if (A) { if (A) { B B C --> C } D D E E } Imagine that is 300 lines long and BCDE contain their own nesting and such. We can do a "git diff -w" and just see that the closing brace moved and that there are no changes in D and E. Do the same in Python and "git diff -w" comes up empty.

teddyh 4y ago

I’ve watched those videos. IIRC, the parentheses always matched.

wrycoder 4y ago

It's not the parentheses or the Polish notation that matter. Those are covered in the first chapter of any Lisp/Scheme book and they are trivial, especially with a proper editor that understands structure and will indent unambiguously accordingly. Unless you're stuck on simple editors like Notepad or Nano, there's no issue here. What's more challenging in Scheme, as Abelson and Sussman teach it, is the use of recursion instead of looping and in particular understanding that recursion is only equivalent to looping when the recursion is in "tail position", i.e. when there is nothing left for the calling function to do except return to its own caller. Common Lisp style tends to use looping, not recursion.