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Comment by xi | Hacker News Reader

Just like semantic indentation, ":" is ABC's heritage. It was discovered that newbie programmers comprehend block operations better when they end with ":".

http://python-history.blogspot.com/2009/02/early-language-de...

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back in time, there was several schools for language syntax design for composite statements:

1. "Open" statements (Pascal):

  IF x 
    THEN s1
    ELSE s2;

  IF x 
    THEN
      BEGIN
        s1;
        s2
      END
    ELSE
      BEGIN
        s3;
        s4
      END

  WHILE c DO s;

  WHILE c DO
  BEGIN
     s1;
     s2
  END

The problem with this design was need to use blocks (BEGIN ... END) and complex rules in case of nesting.

2. "Closed" statements (Algol 68)

  IF x 
    THEN 
       s1;
       s2
    ELSE 
       s3;
       s4
  FI // END IF

  WHILE c DO
     s1;
     s2
  OD // END WHILE

You can see new kind of parenthesis IF-FI, DO-OD, etc.

I more like "closed" syntax. But C syntax with it's brackets blocks "{...}" instead of "BEGIN...END" made this less an issue.

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