🥮 mooncakes.io

/

jq

A jq clone implemented in MoonBit

jq

json

moonbit

Author

Version

0.2.0

License

Apache-2.0

Repository

github.com/mizchi/jq

Last updated

7 months ago

Downloads

2K

#mizchi/jq

A jq clone implemented in MoonBit.

#Install CLI

moon install mizchi/jq/cmd/moonjq

This installs moonjq to ~/.moon/bin/moonjq.

echo '{"name":"alice","age":30}' | moonjq '.name'
# "alice"

echo '[1,2,3,4,5]' | moonjq 'map(. * 2) | add'
# 30

echo '[{"a":1},{"a":2},{"a":3}]' | moonjq '[.[] | select(.a > 1)]'
# [{"a":2},{"a":3}]

#Use as Library

moon add mizchi/jq

let results = @jq.run(".foo", @json.parse("{\"foo\":42}"))
// results = [Number(42)]

// Pre-compile for repeated use
let filter = @jq.compile("map(. + 1)")
let r1 = @jq.run_compiled(filter, @json.parse("[1,2,3]"))
// r1 = [Array([Number(2), Number(3), Number(4)])]

See README.mbt.md for full doc-tested API examples.

#Compatibility

96.2% compatible with jq 1.8.1 (252/262 verified tests).

429 of 514 jq.test cases ported. 496 MoonBit tests total, all passing.

#Supported Features

Category	Features
Basic	., .foo, .[n], .[], .., .[m:n]
Operators	\\|, ,, + - * / %, == != < > <= >=, and or not, //
Assignment	=, \\|=, +=, -=, *=, /=, %=, //=
Construction	[expr], {k: v}, {foo} (shorthand), (expr), "\(.expr)"
Control	if-then-elif-else-end, try-catch, .foo?, foreach, while, until, label/break
Binding	as $x, as [$a,$b], as {a:$x}, ?//, reduce, def
Path	path(), setpath(), getpath(), delpaths(), del(), pick()
Builtins	length, keys, values, type, select, map, map_values, empty, add, sort, sort_by, group_by, unique, unique_by, reverse, flatten, min, max, min_by, max_by, first, last, limit, range, has, contains, inside, any, all, tostring, tonumber, toboolean, tojson, fromjson, ascii_downcase, ascii_upcase, split, join, startswith, endswith, ltrimstr, rtrimstr, trim, ltrim, rtrim, trimstr, abs, fabs, floor, ceil, round, explode, implode, to_entries, from_entries, with_entries, walk, transpose, bsearch, indices, index, rindex, not, recurse, debug, IN, INDEX, error, paths, isempty, nth, skip, builtins, utf8bytelength, $__loc__
Math	sqrt, sin, cos, atan, atan2, log, log2, exp, exp2, pow, infinite, nan, isnan, isinfinite, isfinite, isnormal
Formats	@base64, @base64d, @json, @text, @html, @uri
Types	numbers, strings, booleans, nulls, arrays, objects, iterables, scalars

#Excluded Tests (85 of 514)

Feature	Tests	Notes
import/include	10	Module system (out of scope)
input	1	Multi-input I/O

#Remaining Incompatibilities (10 of 262 tested)

All caused by platform constraints (IEEE 754 double / JS string handling):

Issue	Tests	Detail
Large integers > 2^53	4	Overflow to Infinity instead of exact representation
-0 handling	1	abs on -0.0 outputs 0 instead of -0
NUL byte (\u0000) in strings	2	contains and toboolean misbehave with embedded NUL
path() error message	1	Missing result value in error message
pick(last) negative index	1	Different error from jq
fromjson error message	1	MoonBit JSON parser produces different error text

#Quick Commands

just           # check + test
just fmt       # format code
just check     # type check
just test      # run tests
just moonjq FILTER  # run CLI

#License

Apache-2.0

#mizchi/jq

A jq clone implemented in MoonBit. Provides compile, run, and run_string for JSON query/transform.

#Quick Start

///|
test {
  inspect(
    @jq.run_string(".foo", "{\"foo\":42}"),
    content=(
      #|["42"]
    ),
  )
}

#API

#run_string — One-shot string-based execution

///|
test {
  inspect(
    @jq.run_string("[.[] | select(. > 3)]", "[1,2,3,4,5]"),
    content=(
      #|["[4,5]"]
    ),
  )
}

#run — Execute with Json value

///|
test {
  let input = @json.parse("{\"a\":1,\"b\":2}")
  let results = @jq.run("{sum: (.a + .b)}", input)
  inspect(
    results[0].stringify(),
    content=(
      #|{"sum":3}
    ),
  )
}

#compile + run_compiled — Pre-compile for repeated use

///|
test {
  let filter = @jq.compile("map(. * 2)")
  let r1 = @jq.run_compiled(filter, @json.parse("[1,2,3]"))
  let r2 = @jq.run_compiled(filter, @json.parse("[10,20]"))
  inspect(r1[0].stringify(), content="[2,4,6]")
  inspect(r2[0].stringify(), content="[20,40]")
}

#Error Handling

///|
test {
  let result = @jq.run_string(".foo", "not json") catch {
    @jq.JqError::JqError(msg) => ["Error: " + msg]
  }
  inspect(result[0].has_prefix("Error:"), content="true")
}

#Examples

#Field Access and Pipes

///|
test {
  let input = "{\"user\":{\"name\":\"alice\",\"age\":30}}"
  inspect(
    @jq.run_string(".user.name", input),
    content=(
      #|["\"alice\""]
    ),
  )
  inspect(
    @jq.run_string(".user | keys", input),
    content=(
      #|["[\"age\",\"name\"]"]
    ),
  )
}

#Array Operations

///|
test {
  let arr = "[3,1,4,1,5,9,2,6]"
  inspect(
    @jq.run_string("sort | unique", arr),
    content=(
      #|["[1,2,3,4,5,6,9]"]
    ),
  )
  inspect(
    @jq.run_string("map(. * 2) | add", arr),
    content=(
      #|["62"]
    ),
  )
}

#Reduce

///|
test {
  inspect(
    @jq.run_string("reduce .[] as $x (0; . + $x)", "[1,2,3,4,5]"),
    content=(
      #|["15"]
    ),
  )
}

#Object Construction

///|
test {
  let input = "[{\"name\":\"a\",\"val\":1},{\"name\":\"b\",\"val\":2}]"
  inspect(
    @jq.run_string("map({(.name): .val}) | add", input),
    content=(
      #|["{\"a\":1,\"b\":2}"]
    ),
  )
}

#Conditionals

///|
test {
  inspect(
    @jq.run_string(
      "map(if . > 0 then \"pos\" elif . == 0 then \"zero\" else \"neg\" end)", "[-1,0,1]",
    ),
    content=(
      #|["[\"neg\",\"zero\",\"pos\"]"]
    ),
  )
}

#User-Defined Functions

///|
test {
  inspect(
    @jq.run_string(
      "def double: . * 2; def inc: . + 1; map(double | inc)", "[1,2,3]",
    ),
    content=(
      #|["[3,5,7]"]
    ),
  )
}

#Format Strings

///|
test {
  inspect(
    @jq.run_string("@base64", "\"hello\""),
    content=(
      #|["\"aGVsbG8=\""]
    ),
  )
  inspect(
    @jq.run_string("@base64d", "\"aGVsbG8=\""),
    content=(
      #|["\"hello\""]
    ),
  )
}

JqError

pub(all) suberror JqError {
  JqError(String)
}

Error type for jq compilation and evaluation failures.

impl Show for JqError

ArithOp

pub enum ArithOp {
  Add
  Sub
  Mul
  Div
  Mod
}

Arithmetic operation type used in filter expressions.

impl Show for ArithOp

CmpOp

pub enum CmpOp {
  Eq
  Ne
  Lt
  Gt
  Le
  Ge
}

Comparison operation type used in filter expressions.

impl Show for CmpOp

Filter

pub enum Filter {
  Identity
  RecurseOp
  Field(String)
  Index(Int)
  Slice(Int?, Int?)
  Iterate
  Pipe(Filter, Filter)
  Comma(Filter, Filter)
  Literal(Json)
  ArrayConstruct(Filter?)
  ObjectConstruct(Array[(ObjKey, Filter)])
  Paren(Filter)
  Try(Filter)
  TryCatch(Filter, Filter)
  IfThenElse(Filter, Filter, Filter)
  Binding(Pattern, Filter, Filter)
  Reduce(Filter, Pattern, Filter, Filter)
  FuncDef(String, Array[String], Filter, Filter)
  FuncCall(String, Array[Filter])
  DynIndex(Filter)
  PostfixDynIndex(Filter, Filter)
  DynSlice(Filter, Filter?, Filter?)
  Neg(Filter)
  Arith(ArithOp, Filter, Filter)
  Compare(CmpOp, Filter, Filter)
  LogicAnd(Filter, Filter)
  LogicOr(Filter, Filter)
  Alternative(Filter, Filter)
  Foreach(Filter, Pattern, Filter, Filter, Filter?)
  StringInterp(Array[(String, Filter?)])
  Assign(Filter, Filter)
  Update(Filter, Filter)
  UpdateAlt(Filter, Filter)
  Label(String, Filter)
  Break(String)
  BindingAlt(Array[Pattern], Filter, Filter)
}

A compiled jq filter AST node.

impl Show for Filter

ObjKey

pub enum ObjKey {
  StrKey(String)
  ExprKey(Filter)
}

Object key type: either a static string or a dynamic expression.

impl Show for ObjKey

Pattern

pub enum Pattern {
  PatVar(String)
  PatArray(Array[Pattern])
  PatObject(Array[(String, Pattern)])
}

Pattern for destructuring bind in 'as' expressions.

impl Show for Pattern

compile

fn compile(filter_str : String) -> Filter raise JqError

Compile a jq filter string into a reusable Filter AST.

run

fn run(filter_str : String, input : Json) -> Array[Json] raise JqError

Compile and execute a jq filter string against JSON input.

run_compiled

fn run_compiled(filter : Filter, input : Json) -> Array[Json] raise JqError

Execute a pre-compiled filter against JSON input.

run_string

fn run_string(filter_str : String, input_str : String) -> Array[String] raise JqError

Compile and execute a jq filter, with JSON string input/output.

Source Files

Powered by MoonBit

Site source Report issue Packages Build queue Skills Statistics

© 2026 mooncakes.io