Operators

Jetro has the operators you'd expect plus a small number of extras that come up in JSON work.

Arithmetic

1 + 2          # 3
3 - 1          # 2
2 * 3          # 6
6 / 2          # 3
7 % 3          # 1
-x             # unary negation

+ on strings concatenates: "foo" + "bar" → "foobar".

+ on arrays concatenates: [1,2] + [3] → [1,2,3].

Comparison

a == b         # equality
a != b         # inequality
a < b          # less than
a <= b
a > b
a >= b

== and != work across types (strings to strings, numbers to numbers, etc). Cross-type comparison returns false for == and true for !=.

Logical

a and b        # short-circuit AND
a or b         # short-circuit OR
not a          # negation

Truthiness: null, false, 0, "", [], {} are falsy. Everything else is truthy.

Pipe

value | expr

Evaluates expr with @ bound to value. It is not a method-call shorthand.

DOC:    {"x": 10}
QUERY:  $.x | @ * 2
OUT:    20

QUERY:  $.x | f"got {@}"
OUT:    "got 10"

To call a method, use dot syntax: $.x.upper(), not $.x | upper.

Coalesce

a ?? b

Return a unless it is null, in which case b.

DOC:    {"name": null}
QUERY:  $.name ?? "anon"
OUT:    "anon"

Ternary

Python-style — postfix condition:

"hot" if temp > 30 else "cool"

DOC:    {"temp": 35}
QUERY:  "hot" if $.temp > 30 else "cool"
OUT:    "hot"

Kind tests

v is number
v is string
v is array
v is object
v is null
v is bool

Returns boolean.

QUERY:  $.x is number

Cast

x as int
x as float
x as string
x as bool
x as array
x as object

Coerces the value (or returns null if the cast is impossible — depends on the specific cast).

"42" as int        # 42
42 as string       # "42"

Membership

xs has v           # array membership: true if v is in xs
o  has "k"         # object membership: true if key "k" exists

There is no v in xs operator — that form is a parse error. Use the postfix has operator above, or call .includes(v) (arrays/strings) explicitly:

$.tags.includes("hugo")    # ✓
"hugo" in $.tags           # ✗ parse error

Regex match

s ~= "pattern"

Returns boolean. Uses Rust regex syntax. Bind captures with .captures or .match_first for richer info — see String Search.

Boolean shortcut on patches

In a patch $ { … } body, a key when condition clause skips the assignment when condition is falsy. See Patch.

Examples

DOC:    {"books": [{"year": 1965, "tags": ["sf"]}, {"year": 1989, "tags": ["sf","hugo"]}], "year_floor": 2000}

QUERY:  $.books.filter((@.year > 1970 and @.tags.includes("hugo")) or @.year >= $.year_floor)
OUT:    []

QUERY:  $.books[0].year ?? 9999
OUT:    1965

QUERY:  $.books.map(b => "old" if b.year < 1970 else "new")
OUT:    ["old","new"]

No in operator. Membership in jetro is xs.includes(v) (or xs.has(v) for objects/arrays). There is no v in xs operator — that form is a parse error. Wrap and/or mixes in parens to make precedence unambiguous; jetro follows standard binding (and tighter than or), but parens read clearer.