Expression Lists
Expression lists
There are many places in Rockstar where you can provide a list in place of an expression… and if you can have a list of expressions, and an expression can be a list, things get all wibbly-wobbly and you can go all cross-eyed.
Rock my world
Rock my world with "a" + "b", "c", and "d" + "e" , "f", and "g" + "h" 'n' "i"
Join my world with "-"
Shout my world
(prints: abc-def-ghi)
Reverse takes a string giving -1 times a string
X is "The number "
Y is " si tsaeB eht "
X is with "of", and true and reverse taking Y
The number is 600 with 60 & 6
X is with the number
Shout X (prints: The number of the Beast is 666)
Let’s start with the easy one: a variable list
Variable lists are used to declare the arguments to a function. They can only contain variable names, and variables must be separated by one of:
- A comma
, - An ampersand
& - The keyword
and - The Oxford comma
, and - A nacton
Nacton (n.) The ‘n’ with which cheap advertising copywriters replace the word ‘and’ (as in ‘fish ‘n’ chips’, ‘mix ‘n’ match’, ‘assault ‘n’ battery’), in the mistaken belief that this is in some way chummy or endearing.
- "The Meaning of Liff", Douglas Adams & John Lloyd
Rockstar supports both the UK nacton 'n' (as in fish ‘n’ chips) and the US nacton n' (as in Guns n’ Roses.)
Sum takes x, y, z giving x + y + z
Product takes x & y giving x * y
My Michelle takes Axl and Slash, Duff & Izzy, and Steven
Shout Axl. Shout Slash. Shout Duff! Shout Izzy
Shout Steven, yeah.
Jungle Love takes Prince, Morris Day and the Time
Shout Prince with Morris Day & the Time, Morris Day & the Time, oh
Shout sum taking 1, 2, 3
Whisper product taking 5, 6
Call my Michelle with "A", "B", "C", "D", and "E"
Call Jungle Love with "oh", "-we", "-oh"
Then there’s a primary list, used to provide arguments to a function. The elements in a primary list must be primaries, and you can’t separate a primary list with an Oxford comma - if the parser sees , and, that means the primary list is finished and move on to the next thing.
The jungle takes Axl and Slash, Duff & Izzy, and Steven
Shout Axl! Shout Slash! Shout Duff! Shout Izzy! Shout Steven, yeah!
Add takes x and y giving x + y
The city is dark
the fire is on fire
Add taking 3 & 4
Call the jungle with 1, 2, 3 & 4 'n' 5
The jungle taking "Guns" 'n' "and" & " n'" & "and" & "Roses"
Rockstar grammar supports three different kinds of lists:
- Expression lists
- Variable lists
- Primary lists
Foo is 1 with 2 + 3, 4, 5 and 6, bar taking 7, 8 and 9, 10, “yeah”
First, 8 and 9 cannot be a function argument (functions only accept primaries), so bar taking 7 is an expression:
Foo is 1 with 2 + 3, 4, 5 and 6, (bar taking 7), 8 and 9, 10, “yeah”
Second, ` and ` (with no leading comma) is always the logical-and operator, and the right-hand operand in a logic expression can’t be a list:
Foo is 1 with 2 + 3, 4, (5 and 6), (bar taking 7), (8 and 9), 10, “yeah”
So now we propagate the + operator to each adjacent pair of arguments
Foo is 1 + 2 + 3 + 4 + (5 and 6) + (bar taking 7) + (8 and 9) + 10 + yeah
So from the left:
1 with (2 + 3, 4, )
The most restrictive is the primary list, used in compound arithmetic expressions:
Elements in a primary list must be primary expressions. A primary expression in Rockstar is anything which yields a value without using any operators. Primaries are literal strings and numbers, variables, function calls, and language constants.
Elements in a primary list are separated by one of:
- Comma
, - Ampersand
& - A nacton
Next, there are expression lists. An expression list supports the same separators as the primary list, but also supports the Oxford comma separator , and Because you can’t put an Oxford comma in a primary list, this means an expression list can contain expressions that themselves contain primary lists; the Oxford comma provides an unambiguous way to separate the sub-expressions.
Expression lists are supported as arguments to compound expressions and when rocking arrays:
Rock my world
Rock my world with "a" + "b", "c", and "d" + "e" , "f", and "g" + "h" 'n' "i"
Join my world with "-"
Shout my world
(prints: abc-def-ghi)
Reverse takes a string giving -1 times a string
X is "The number "
Y is " si tsaeB eht "
X is with "of", and true and reverse taking Y
The number is 600 with 60 & 6
X is with the number
Shout X (prints: The number of the Beast is 666)
Finally, there are variable lists, used to specify the arguments when defining a function.
Because the elements in the list can only be variable names, a variable list supports all the separators used in primary and expression lists, and also the bareword ` and ` (with no commas or punctuation required).