1 2 3 makes a list of numbers, why doesn't a b c do that when they are all numeric?
J beginners, learning that 1 2 3 is a 3-element vector of numbers, often reach the erroneous conclusion that space is a concatenation operator in J, and that two nouns appearing side-by-side are concatenated. They are then surprised by
1 2 3 NB. create a list 1 2 3 a =: 1 b =: 2 c =: 3 a b c NB. Why doesn't this create the same list? |syntax error | a b c
Space is not a concatenation operator. , (comma) is the concatenation verb. Lists of consecutive numbers are a special case. They are recognized during the initial analysis of a sentence, before execution begins. a b c can't be recognized at that point, because the values of a, b, and c may change during execution of the sentence.
Contributed by HenryRich