A couple of months ago, I opened an issue regarding functions called true(), false() and null() that didn't work as expected.

Today, I found out functions called and(), or() and not() are even worse. Both and() and or() returns a syntax error when called (not declared):

@function and() {
  @return "and"
}

test {
  and: and();
}

Invalid CSS after " and: ": expected expression (e.g. 1px, bold), was "and();"

@function or() {
  @return "or"
}

test {
  or: or();
}

Invalid CSS after " or: ": expected expression (e.g. 1px, bold), was "or();"

The not() function on the other side partially works. It doesn't throw any error but it returns false, no matter what.

@function not() {
  @return "not"
}

test {
  not: not();
}

test {
  not: false;
}

Tested on Sass 3.3.6 and 3.2.19. Curious things is everything works like a charm with LibSass.