3 ms·

Why are people upvoting this as if it wasn't just explained why that's not true? That's only possible when you have (mandatory) block delimiters. That was the

by cxr 5y ago

Why are people upvoting this as if it wasn't just explained why that's not true? That's only possible when you have (mandatory) block delimiters. That was the entire basis of the comment—that `elif` is used in "languages that don't have an explicit block statement with its own delimiters".

xigoi 5y ago
How is it not possible? Here's a simple grammar: if_stmt <- "if" expr INDENT stmts DEDENT ("else" "if" expr INDENT stmts DEDENT)* ("else" INDENT stmts DEDENT)? It does require one-token lookahead, but it's unambiguous.
- deleted 5y ago
  [deleted]
- cxr 5y ago
  Are INDENT and DEDENT here describing whitespace sensitivity in the vein of Python, which "uses whitespace to delimit control flow blocks"[1] (elsewhere[2]: "Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks")? We're specifically talking about the subset of languages where these blocks _don't_ have their own delimiters[3]. 1. https://en.wikipedia.org/w/index.php?title=Python_syntax_and https://en.wikipedia.org/w/index.php?title=Python_syntax_and... 2. https://en.wikipedia.org/w/index.php?title=Python_(programmi https://en.wikipedia.org/w/index.php?title=Python_(programmi... 3. There is a reading of Bob's original comment such that it's suggesting that Python and end-if languages are among languages without them (or something—I can't make total sense of that part of the comment; it gets kind of garden path-y), but they're not.
  - xigoi 5y ago
    It doesn't matter how indentation is parsed. What I wanted to say that you can simply replace "elif" with "else" "if" in the grammar.
- munificent 5y ago
  You're right, you could do this in Python because it uses indentation for block delimiting. That means this is unambiguous: if c1 then: s1 else if c2: s2 s3 Without significant indentation, it's not possible to tell if "s3" is indented to be part of the the second if's then branch. In other words, "else if" and "else INDENT if" are unambiguously different in Python. That's not true in other languages that use "elif"/"elsif"/"elseif" where only newlines are significant and not indentation.

by cxr 5y ago

xigoi 5y ago

How is it not possible? Here's a simple grammar: if_stmt <- "if" expr INDENT stmts DEDENT ("else" "if" expr INDENT stmts DEDENT)* ("else" INDENT stmts DEDENT)? It does require one-token lookahead, but it's unambiguous.

deleted 5y ago
[deleted]
cxr 5y ago
Are INDENT and DEDENT here describing whitespace sensitivity in the vein of Python, which "uses whitespace to delimit control flow blocks"[1] (elsewhere[2]: "Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks")? We're specifically talking about the subset of languages where these blocks _don't_ have their own delimiters[3]. 1. https://en.wikipedia.org/w/index.php?title=Python_syntax_and https://en.wikipedia.org/w/index.php?title=Python_syntax_and... 2. https://en.wikipedia.org/w/index.php?title=Python_(programmi https://en.wikipedia.org/w/index.php?title=Python_(programmi... 3. There is a reading of Bob's original comment such that it's suggesting that Python and end-if languages are among languages without them (or something—I can't make total sense of that part of the comment; it gets kind of garden path-y), but they're not.
- xigoi 5y ago
  It doesn't matter how indentation is parsed. What I wanted to say that you can simply replace "elif" with "else" "if" in the grammar.
munificent 5y ago
You're right, you could do this in Python because it uses indentation for block delimiting. That means this is unambiguous: if c1 then: s1 else if c2: s2 s3 Without significant indentation, it's not possible to tell if "s3" is indented to be part of the the second if's then branch. In other words, "else if" and "else INDENT if" are unambiguously different in Python. That's not true in other languages that use "elif"/"elsif"/"elseif" where only newlines are significant and not indentation.