Wiki: Rockstar

Replace is with 's (removing the leading whitespace)
n's- is the shortest way to initialize a variable to one.
- similarly, a string starting with any of ,+-*/& can be initialized with say to save one byte (n say* instead of n = "*")
Some operators like + take multiple arguments, so you can abuse it like s+" "i instead of s+" "+i
turn up/turn down to round
- To get x remainder y: t = x/y, turn down t, x-t*y is the remainder
- Where possible, using turn up to get the remainder saves 2 bytes: t =-x/y, turn up t, x+t*y is the remainder
- Or to just check for divisibility, you can use turn up instead
In rock x with y, the with is unneeded, rock x y works
cut can split by an int, like cut "a0b0c"with 0into x
Steal stuff from Java: off java,math play BigDecimal
means to alias: e.g. you use taking a lot to call a function, use t means taking and then use t

Rounding

x+8e15-8e15 to round to the nearest integer
- x+8e15-8e15is x to check if x is an integer
- x/y+8e15-8e15is x/y to check if x is divisible by y (see another way in the next section)

String operators

s/1 or s-0 to cast the string s to a number
- s--n to cast s and add n
s*n rounds n down before multiplying, i.e. "a"*2.7 is equal to "aa"
- x/y*"a" is truthy if x ≥ y
- x/y*"a"y's x*"a" to check if x is divisible by y (might be slow)
x+"."is x is another way to check if x is an integer, but is signficantly slower than using rounding
0is "0e"+x to check if x is an integer (might be useful if x is a string or if you don't want to repeat x twice)
x+"0"is x to check if x is a non-integer number (or 0)
- x+"0"-x is truthy if x is an integer number (except for 0)
""*"" (or s*s if s is a string) can be used to get the value mysterious.

Array operators

push x 2,3,4,5
t = x+6 (t = 2,3,4,5,6)
t = 1+x (t = 1,2,3,4,5)
t = x+x (t = 2,3,4,5,2,3,4,5)
t = x-2 (removes 2nd element: t = 2,3,5)

Any other arithmetic operation converts the array to its length:

t = 0-x (t = -4)

void returns an empty array, you can use it to generate an array on the fly:

while void+2+3+5+7+11as x
say x

For each

while v
say pop v

is one byte shorter than

while v as x
say x

Into

t = x
cut t

is one byte shorter than

cut x into t

`it`

it is kinda hard to use. It takes the value of the variable that was most recently assigned to. This can be used in a couple ways, most notably to take the value of args at the start of the program (after the hidden boilerplate assigns it).

while args as r
while it as r

it can also be used as a condition in general, even in holes with no input. it will just be equivalent to an empty array at the start of the program.

until it
...
_ = cond

Try reusing your existing assignments as the condition, or doing some operation that errors out. This can be combined with using an array as a counter to avoid initialising variables altogether.

while 10-it
rock i 0
say i

A final use is checking whether an if statement or while statement executed at all, though this is harder to pull off.

i = 0
while cond
k = ...

say it