Operators

Operators are listed from the loosest binding to the tightest. Use brackets when you are not sure.

Arithmetic

+, -, *, /, % (remainder) and ** (power). A value that is not a number reads as 0, a numeric string such as "12" reads as a number, and dividing by zero gives 0 in a form.

1 + 2 * 3

7

(1 + 2) * 3

9

10 / 4

2.5

10 % 3

1

2 ** 3

8

5 / 0

0

A minus sign binds tighter than **, so -2 ** 2 is 4, not -4. Write -(2 ** 2) for -4.

-2 ** 2

4

Joining text

~ joins two values as text. It binds looser than +, so the sum is worked out first.

{"answers": {"first": "Ada", "last": "Lovelace"}}

answers.first ~ " " ~ answers.last

"Ada Lovelace"

"n=" ~ 1 + 2

"n=3"

Comparison

==, !=, <, >, <= and >=. Two numbers compare as numbers and two texts compare as text. You can chain them: a < b < c is true when all three hold, and b is read once.

{"answers": {"age": 21, "role": "manager", "a": 1, "b": 2, "c": 3}}

answers.age >= 18

true

answers.role == "manager" ? "M" : "O"

"M"

answers.a < answers.b < answers.c

true

answers.missing == null

true

Dates compare as dates once they are parsed. See Methods.

Words for comparison

The condition builder, and you, can write the comparisons as words: is greater than, is not less than, is greater than or equal to.

{"answers": {"x": 3}}

answers.x is not less than 3

true

answers.x is greater than or equal to 3

true

Logic

&& and ||, or and and or, and ! or not. They stop as soon as the answer is known. not binds looser than a comparison, so not answers.x == 3 means not (answers.x == 3).

{"answers": {"age": 16, "consent": true, "x": 3}}

answers.age >= 18 && answers.consent == true

false

not answers.x == 3

false

answers.age >= 18 or answers.consent

true

Which values count as false: false, null, 0, "". An empty list is true. Use is_empty when you mean “has no answer”.

The ternary

condition ? then : else picks one of two values. It is how a computed value changes with an answer.

answers.age >= 18 ? "adult" : "minor"

"minor"

Fallback with ??

a ?? b is a unless a is null, and then b. A cleared text box is "", not null, so ?? keeps it. Use coalesce when you want the first non-null of several.

answers.nickname ?? "Anon"

"Anon"

Membership with in

x in list is true when the value is in the list. It also works on a range and on text.

{"answers": {"country": "GB", "x": 3}}

answers.country in ["US", "GB"]

true

"ell" in "hello"

true

Ranges

a...b is the whole numbers from a to b, with both ends. a..<b leaves out b. A range counting down is a list counting down. A range can have at most 100000 entries.

answers.x in 1...9

true

answers.x in 1..<3

false

9...7

[9,8,7]

Matching text

value matches /pattern/ tests a regular expression. The match is not anchored, so use ^ and $ for the whole value. The builtin match(value, /pattern/) does the same.

{"answers": {"email": "[email protected]", "code": "ABC"}}

answers.email matches /.+@.+\..+/

true

match(answers.code, /^[A-Z]{3}$/)

true

Lists and records

[1, 2, 3] is a list and {a: 1, b: 2} is a record. Read a list entry with answers.tags[0].

{"answers": {"tags": ["x", "y"]}}

answers.tags[0]

"x"

len([1, 2, 3])

3