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Module B0_json.JsonqSource

JSON value queries.

TODO maybe we could expose a bit more options for error reporting. In particular the internal path type and a combinator in the vein of loc to report back the path trace. Basically see Serialk_sexp.

Queries

Sourcetype 'a t

The type JSON value queries. A query either fails or succeeds against a JSON value returning a value of type 'a.

Sourceval query : 'a t -> Json.t -> ('a, string) result

query q j is Ok v if que query q succeeds on s and a (multiline) Error e otherwise.

Success and failure

Sourceval succeed : 'a -> 'a t

succeed v is a query that succeeds with value v on any JSON value.

Sourceval fail : string -> 'a t

fail msg is a query that fails on any JSON value with message msg. Do not include position information in msg, this is automatically handled by the module.

Sourceval failf : ('a, Format.formatter, unit, 'b t) format4 -> 'a

failf fmt ... is like fail but formats the message according to fmt.

Query combinators

Sourceval app : ('a -> 'b) t -> 'a t -> 'b t

app fq q queries a s-expression first with fq and then with q and applies the result of latter to the former.

Sourceval ($) : ('a -> 'b) t -> 'a t -> 'b t

f $ v is app f v.

Sourceval pair : 'a t -> 'b t -> ('a * 'b) t

pair q0 q1 queries first with q0 and then with q1 and returns the pair of their result.

Sourceval bind : 'a t -> ('a -> 'b t) -> 'b t

bind q f queries a s-expression with q, applies the result to f and re-queries the s-expression with the result.

Sourceval map : ('a -> 'b) -> 'a t -> 'b t

map f q is app (succeed f) q.

Sourceval some : 'a t -> 'a option t

some q is map Option.some q.

JSON queries

Sourceval fold : null:'a t -> bool:'a t -> float:'a t -> string:'a t -> array:'a t -> obj:'a t -> 'a t

fold queries JSON values according to their kind using the provided queries.

Sourceval partial_fold : ?null:'a t -> ?bool:'a t -> ?float:'a t -> ?string:'a t -> ?array:'a t -> ?obj:'a t -> unit -> 'a t

partial_fold is like fold but only queries the kinds that are explicitely specified. It errors on other kinds.

Sourceval json : Json.t t

json queries any JSON value and returns it.

Sourceval loc : Json.loc t

locis map Sexp.loc sexp.

Sourceval with_loc : 'a t -> ('a * Json.loc) t

with_loc q queries with q and returns the result with the location of the queried JSON value.

Nulls

Sourceval is_null : bool t

is_null tests for a JSON null value.

Sourceval null : unit t

null queries JSON null as unit and fails otherwise.

Sourceval nullable : 'a t -> 'a option t

nullable q is None on JSON null and otherwise queries the value with q.

Atomic values

Sourceval bool : bool t

bool queries JSON bool values as a bool value and fails otherwise.

Sourceval float : float t

float queries JSON number values as a float value and fails otherwise.

Sourceval int : int t

int is map truncate float.

Sourceval string : string t

string queries JSON string values as a string value and fails otherwise.

Sourceval string_to : kind:string -> (string -> ('a, string) result) -> 'a t

string_to ~kind parse queries a JSON string and parses it with p. In case of Error m error fails with m. kind is the kind of value parsed, it is used for the error in case no JSON string is found.

Sourceval enum : kind:string -> Set.Make(String).t -> string t

enum ~kind ss queries a JSON string for one of the elements of ss and fails otherwise. kind is for the kind of elements in ss, it used for error reporting.

Sourceval enum_map : kind:string -> 'a Map.Make(String).t -> 'a t

enum_map ~kind sm queries a string for it's map in sm and fails if the string is not bound in sm. kind is for the kind elements in sm, it is used for error reporting.

Arrays

These queries only succeed on JSON array values.

Sourceval is_empty_array : bool t

is_empty_array queries an array for emptyness.

Sourceval hd : 'a t -> 'a t

hd q queries the first element of an array with q. Fails on empty arrays.

Sourceval tl : 'a t -> 'a t

tail q queries the tail of an array with q. Fails on empty arrays.

Sourceval fold_array : ('a -> 'b -> 'b) -> 'a t -> 'b -> 'b t

fold_array f q acc queries the elements of an array from left to right with q and folds the result with f starting with acc.

Sourceval array : 'a t -> 'a list t

array q queries the elements of an array with q.

Array index queries

Sourceval nth : ?absent:'a -> int -> 'a t -> 'a t

nth ?absent n q queries the nth element of an array with q. If n is negative counts from the end of the array, so -1 is the last array element. If the element does not exist this fails if absent is None and succeeds with v if absent is Some v.

Objects

These queries only succeed on JSON object values.

Sourceval mem : string -> 'a t -> 'a t

mem n q queries the member n of a JSON object with q. The query fails if n is unbound in the object.

Sourceval opt_mem : string -> 'a t -> absent:'a -> 'a t

opt_mem n q ~absent queries the member n of a JSON object with q. absent is returned if n is unbound in the object.

Sourceval mem_dom : validate:Set.Make(String).t option -> Set.Make(String).t t

mem_dom ~validate queries the member domain of a JSON object. If validate is Some dom, the query fails if a member name is not in dom.