Comment by jeffdavis

7 years ago

The {} construct seems awfully close to NULL. Not sure I understand the fundamental difference -- having a third value in boolean contexts still introduces 3VL.

Why not just use an Option/Maybe type?

3 comments

jeffdavis

RedCrowbar 7 years ago

Empty set differs from NULL is that you get an empty set if you apply an element-wise function over it (which most operators and functions in EdgeQL are).

> Why not just use an Option/Maybe type?

We are considering adding algebraic types and a syntax to match them, but it ultimately boils down to taste and use case:

  SELECT value ?? "fallback in case of empty"

is not fundamentally different from (hypothetical):

  SELECT 
    MATCH value
    CASE Some(non_empty_val) THEN non_empty_val
    CASE Empty THEN "fallback in case of empty"
    END;

jeffdavis 7 years ago
"Empty set differs from NULL is that you get an empty set if you apply an element-wise function over it"
It still sounds like NULL -- I must be missing something.
- RedCrowbar 7 years ago
  
  Take the CASE WHEN example from the blog. An equivalent EdgeQL expression is
  SELECT 'one' IF value = 1 ELSE 'not one'
  If value is an empty set, then the result is _always_ an empty set, unlike SQL that pretends NULL values are actually boolean for the purposes of the condition. EdgeQL expressions are, essentially, set comprehensions, the above is equivalent to this Python expression:
  {'one' if v = 1 else 'not one' for v in value}