Language Cheatsheet

Assignment and Equality

# assign variable x to value of field foo.bar.baz in input
x := input.foo.bar.baz
# check if variable x has same value as variable y
x == y
# check if variable x is a set containing "foo" and "bar"
x == {"foo", "bar"}
# OR
{"foo", "bar"} == x

Lookup

Arrays

# lookup value at index 0
val := arr[0]
 # check if value at index 0 is "foo"
"foo" == arr[0]
# find all indices i that have value "foo"
"foo" == arr[i]
# lookup last value
val := arr[count(arr)-1]

Objects

# lookup value for key "foo"
val := obj["foo"]
# check if value for key "foo" is "bar"
"bar" == obj["foo"]
# OR
"bar" == obj.foo
# check if key "foo" exists and is not false
obj.foo
# check if key assigned to variable k exists
k := "foo"
obj[k]
# check if path foo.bar.baz exists and is not false
obj.foo.bar.baz
# check if path foo.bar.baz, foo.bar, or foo does not exist or is false
not obj.foo.bar.bar

Sets

# check if "foo" belongs to the set
a_set["foo"]
# check if "foo" DOES NOT belong to the set
not a_set["foo"]
# check if the array ["a", "b", "c"] belongs to the set
a_set[["a", "b", "c"]]
# find all arrays of the form [x, "b", z] in the set
a_set[[x, "b", z]]

Iteration

Arrays

# iterate over indices i
arr[i]
# iterate over values
val := arr[_]
# iterate over index/value pairs
val := arr[i]

Objects

# iterate over keys
obj[key]
# iterate over values
val := obj[_]
# iterate over key/value pairs
val := obj[key]

Sets

# iterate over values
set[val]

Advanced

# nested: find key k whose bar.baz array index i is 7
foo[k].bar.baz[i] == 7
# simultaneous: find keys in objects foo and bar with same value
foo[k1] == bar[k2]
# simultaneous self: find 2 keys in object foo with same value
foo[k1] == foo[k2]; k1 != k2
# multiple conditions: k has same value in both conditions
foo[k].bar.baz[i] == 7; foo[k].qux > 3

For All

# assert no values in set match predicate
count({x | set[x]; f(x)}) == 0
# assert all values in set make function f true
count({x | set[x]; f(x)}) == count(set)
# assert no values in set make function f true (using negation and helper rule)
not any_match
# assert all values in set make function f true (using negation and helper rule)
not any_not_match

any_match {
    set[x]
    f(x)
}
any_not_match {
    set[x]
    not f(x)
}

Rules

In the examples below ... represents one or more conditions.

Constants

a = {1, 2, 3}
b = {4, 5, 6}
c = a | b

Conditionals (Boolean)

# p is true if ...
p = true { ...}
# OR
p { ... }

Conditionals

default a = 1
a = 5 { ... }
a = 100 { ... }

Incremental

# a_set will contain values of x and values of y
a_set[x] { ... }
a_set[y] { ... }
# a_map will contain key->value pairs x->y and w->z
a_map[x] = y { ... }
a_map[w] = z { ... }

Ordered (Else)

default a = 1
a = 5 { ... }
else = 10 { ... }

Functions (Boolean)

f(x, y) {
    ...
}
# OR
f(x, y) = true {
    ...
}

Functions (Conditionals)

f(x) = "A" { x >= 90 }
f(x) = "B" { x >= 80; x < 90 }
f(x) = "C" { x >= 70; x < 80 }

Patterns

Merge Objects

merge_objects({"a": true, "b": false}, {"b": "foo", "c": 4})

has_key(x, k) { _ = x[k] }
pick_first(k, a, b) = a[k]
pick_first(k, a, b) = b[k] { not has_key(a, k) }
merge_objects(a, b) = c {
    ks := {k | some k; _ = a[k]} | {k | some k; _ = b[k]}
    c := {k: v | some k; ks[k]; v := pick_first(k, b, a)}
}

Tests

# define a rule that starts with test_
test_NAME { ... }
# override input.foo value using the 'with' keyword
data.foo.bar.deny with input.foo as {"bar": [1,2,3]}}