# std/jsondec The untyped half of `fromJson`, and the generator of the typed half. `jsonDecoders` writes the typed half per target type. What it writes reads the source once through a `JsonReader` and decodes each value into its slot; it builds no `Json` tree. It calls this module for the reader, `Issue`s, paths and scalar decoders. Decoding accumulates: a decoder records its failure and returns, and a composite constructs only when every part succeeded. So every decoder returns an `Array` of zero or one element; empty means the issue is already recorded. `Option` cannot serve: with `T = Option` it has no wire form. Every message is the canonical wording, byte for byte. A refused document yields its `json.parse` Issue alone, and a record's Issues follow its members' declaration order, whatever the document's key order. The tree accessors (`fieldsOf`, `fieldAt` and the rest) serve programs that read a `Json` from `parseJson`. ## fieldsOf `fn`, at line 25. ```vyrn fn fieldsOf(v: Json) -> Array ``` An object's fields in document order, or `[]` for anything else. ## itemsOf `fn`, at line 37. ```vyrn fn itemsOf(v: Json) -> Array ``` An array's items, or `[]` for anything else. ## numText `fn`, at line 49. ```vyrn fn numText(v: Json) -> String ``` A number's raw source text, or `""` for anything else. ## hasField `fn`, at line 61. ```vyrn fn hasField(fs: Array, key: String) -> Bool ``` Whether an object carries `key` at all (a present `null` is still present). ## fieldAt `fn`, at line 71. ```vyrn fn fieldAt(fs: Array, key: String) -> Json ``` The value of `key`, or `JNull` when absent. ## elemAt `fn`, at line 81. ```vyrn fn elemAt(items: Array, i: Int64) -> Json ``` Element `i`, or `JNull` when the index is past the end. ## tagOf `fn`, at line 90. ```vyrn fn tagOf(v: Json) -> String ``` A bare string's content (a nullary enum variant's wire form), or `""`. No variant can be named `""`, so the sentinel cannot collide with a real tag. ## pushType `fn`, at line 102. ```vyrn fn pushType(iss: modify Array, path: String, expected: String, found: String) -> Unit ``` `json.type`: `expected , found `. ## pushMissing `fn`, at line 111. ```vyrn fn pushMissing(iss: modify Array, path: String, field: String) -> Unit ``` `json.missing`: `missing required field `name``. ## pushValidate `fn`, at line 122. ```vyrn fn pushValidate(iss: modify Array, path: String, message: String) -> Unit ``` `validate`: a refined type's `where` clause did not hold. The caller passes the compiler's validation message, so the trap and this path word it the same. ## fieldPath `fn`, at line 127. ```vyrn fn fieldPath(parent: String, field: String) -> String ``` A dotted path extended by a record field (or an enum tag). ## indexPath `fn`, at line 135. ```vyrn fn indexPath(parent: String, i: Int64) -> String ``` A path extended by an array index. ## pathAt `fn`, at line 143. ```vyrn fn pathAt(path: String, seg: String, idx: Int64) -> String ``` The path of a value a decoder reads: `path` itself when `idx` is `-2`, `path[idx]` for an element, and `path.seg` for a member when `idx` is `-1`. A decoder builds it only for an Issue or for its own members, so a value that decodes builds no path. ## openDoc `fn`, at line 157. ```vyrn fn openDoc(src: String) -> JsonReader ``` A reader over `src`. ## closeDoc `fn`, at line 162. ```vyrn fn closeDoc(p: modify JsonReader) -> Array ``` Ends a decode: `[]`, or the one `json.parse` Issue of a refused document. ## kindAt `fn`, at line 172. ```vyrn fn kindAt(p: JsonReader) -> Int64 ``` The kind of the value at the cursor, as `std/jsonread`'s `kindAt` names it. ## kindName `fn`, at line 176. ```vyrn fn kindName(k: Int64) -> String ``` ## expect `fn`, at line 183. ```vyrn fn expect( p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array, kind: Int64, what: String, ) -> Bool ``` Whether the value at the cursor is of `kind`, a `kindAt` kind. If it is not, records `expected , found ` at the value's path (see `pathAt`) and reads the value past. ## readNull `fn`, at line 203. ```vyrn fn readNull(p: modify JsonReader) -> Bool ``` Reads a `null` at the cursor and answers whether there was one: the wire form of an absent `Option`. ## readString `fn`, at line 211. ```vyrn fn readString(p: modify JsonReader) -> String ``` ## skipValue `fn`, at line 215. ```vyrn fn skipValue(p: modify JsonReader) -> Unit ``` ## enterObject `fn`, at line 219. ```vyrn fn enterObject(p: modify JsonReader) -> Bool ``` ## enterArray `fn`, at line 223. ```vyrn fn enterArray(p: modify JsonReader) -> Bool ``` ## readKey `fn`, at line 227. ```vyrn fn readKey(p: modify JsonReader) -> String ``` ## keyIs `fn`, at line 231. ```vyrn fn keyIs(p: modify JsonReader, name: String) -> Bool ``` ## nextMember `fn`, at line 235. ```vyrn fn nextMember(p: modify JsonReader) -> Bool ``` ## nextItem `fn`, at line 239. ```vyrn fn nextItem(p: modify JsonReader) -> Bool ``` ## keySet `fn`, at line 243. ```vyrn fn keySet() -> JsonKeySet ``` ## member `fn`, at line 249. ```vyrn fn member(p: modify JsonReader, seen: Bool, key: String) -> Unit ``` Reads past the `:` after a record member's `key`, or refuses the key as a duplicate when the member was `seen`. ## mapMember `fn`, at line 259. ```vyrn fn mapMember(p: modify JsonReader, keys: modify JsonKeySet, key: String) -> Bool ``` Records `key` in `keys` and reads past the `:`, answering `true`; or refuses the key as a duplicate and answers `false`. ## skipMember `fn`, at line 269. ```vyrn fn skipMember(p: modify JsonReader, keys: modify JsonKeySet, key: String) -> Unit ``` Reads a member no field claims: an unknown field is ignored, but its key may not repeat and its value must be JSON. ## takeIssues `fn`, at line 277. ```vyrn fn takeIssues(iss: modify Array, base: Int64) -> Array ``` Moves `iss[base..]` out, in order: a record puts its members' Issues back in declaration order with `putIssues`. ## putIssues `fn`, at line 291. ```vyrn fn putIssues(iss: modify Array, late: Array, a: Int64, b: Int64) -> Unit ``` Appends `late[a..b]`, end excluded, to `iss`. ## dStr `fn`, at line 303. ```vyrn fn dStr(p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array) -> Array ``` ## dBool `fn`, at line 311. ```vyrn fn dBool(p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array) -> Array ``` ## dInt64 `fn`, at line 321. ```vyrn fn dInt64(p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array) -> Array ``` A JSON integer-syntax number as an exact `Int64`. A fraction, an exponent or a magnitude outside `Int64` is `expected integer`, never a rounded value. ## dIntKey `fn`, at line 328. ```vyrn fn dIntKey(key: String, path: String, iss: modify Array) -> Array ``` An object key read as an `Int64`, the wire form of `Map`, in the map at `path`. Only the canonical text (`n.toString()`) passes: `"007"` and `"+7"` would otherwise collapse into the key `"7"` with no Issue. ## dIntRange `fn`, at line 341. ```vyrn fn dIntRange( p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array, lo: Int64, hi: Int64, ) -> Array ``` `dInt64` restricted to `[lo, hi]`, for the sized signed integers. ## dUIntMax `fn`, at line 366. ```vyrn fn dUIntMax( p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array, hi: UInt64, ) -> Array ``` A JSON integer-syntax number as an exact `UInt64` in `[0, hi]`. `parseInt64` cannot serve: it has no room above `Int64.max`. ## dFloat64 `fn`, at line 390. ```vyrn fn dFloat64(p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array) -> Array ``` A JSON number as a `Float64`, correctly rounded (`std/num`). Integer syntax is accepted: `1` decodes into a `Float64` target as `1.0`. ## dFloat32 `fn`, at line 405. ```vyrn fn dFloat32(p: modify JsonReader, path: String, seg: String, idx: Int64, iss: modify Array) -> Array ``` A JSON number as a `Float32`, rounded once: decimal -> `Float64` -> `Float32` rounds twice and is wrong near a `Float32` tie. ## jsonDecoders `fn`, at line 425. ```vyrn gen fn jsonDecoders(t: TypeArg) -> String ``` Writes the decoders `fromJson` calls: for each root, the entry that reads a document into `Validation`, and for each node, the function that decodes the value at a reader's cursor into zero or one value. Generated source cannot spell reserved names, so it writes `VyrnRt_` for `std/json`'s, `VyrnRd_` for this module's and `VyrnWp_` for a `where` type's predicate. --- From https://vyrn-lang.github.io/docs/std/jsondec.html — generated by `site/export.vyrn` from the Vyrn repository.