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\n\n## All commands\n| Command | Description | flags & args | Example |\n|------------|----------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|\n| `.open` | Interactive command to open a template (defaults to examples folder) | | `.open` |\n| `.cd` | Change directory (then use .open command) | | `.cd ..` |\n| `.init` | Initialize the template from a JSON file. | • `-f • `--tags=
•`--options=
• `--xf=
• `--importPath=
• `--tail \"
`.out /data/accounts` |\n| `.state` | Show the current state of the template metadata. | `None` | `.state` |\n| `.plan` | Show the execution plan for rendering the template. | `None` | `.plan` |\n| `.note` | Show a separator line with a comment in the REPL output. | `
`.tail \"/ until foo='bar'\"` |\n| `.svg` | Serve an SVG diagram of the DAG | `--port
• `--tags=
• `--xf=
• `--importPath=
• `--tail \"
![\"Alt](\"https://raw.githubusercontent.com/geoffhendrey/jsonataplay/main/tailgraphs.gif\")
\n\n# Reactive Behavior\nStated is naturally reactive. In the example below, `story` will evaluate when the promises for `partI` and `partII` have both\nresolved, simply because `story` has references to `partI` and `partII`, each of which respectively is triggered by the \nresolution of the two fetch functions they each depend on.\n```json\n> .init -f \"example/ex21.json\"\n{\n \"call\": \"${function($url){$fetch($url) ~> handleRes}}\",\n \"falcon\": \"${ call('https://swapi.tech/api/starships/?name=Millennium').result[0].properties.name}\",\n \"han\": \"${ call('https://swapi.tech/api/people/?name=han').result[0].properties.name}\",\n \"handleRes\": \"${ function($res){$res.ok? $res.json():$res.status?{'status': $res.status}:$res} }\",\n \"luke\": \"${ call('https://swapi.tech/api/people/?name=luke').result[0].properties.name}\",\n \"partI\": \"${ [han, 'piloted the', falcon] ~> $join(' ')}\",\n \"partII\": \"${ [luke, 'piloted the', xwing] ~> $join(' ')}\",\n \"story\": \"${ [partI, 'then', partII]~>$join(' ')}\",\n \"xwing\": \"${ call('https://swapi.tech/api/starships/?name=x-wing').result[0].properties.name}\"\n}\n> .plan\n[\n \"/handleRes\",\n \"/call\",\n \"/falcon\",\n \"/han\",\n \"/luke\",\n \"/partI\",\n \"/xwing\",\n \"/partII\",\n \"/story\"\n]\n> .out\n{\n \"story\": \"Han Solo piloted the Millennium Falcon then Luke Skywalker piloted the X-wing\",\n \"handleRes\": \"{function:}\",\n \"call\": \"{function:}\",\n \"partI\": \"Han Solo piloted the Millennium Falcon\",\n \"luke\": \"Luke Skywalker\",\n \"xwing\": \"X-wing\",\n \"partII\": \"Luke Skywalker piloted the X-wing\",\n \"han\": \"Han Solo\",\n \"falcon\": \"Millennium Falcon\"\n} \n```\n## SVG command\nThe .svg command serves an SVG diagram of the DAG\n```json [false, \"$='http://localhost:4042'\"]\n> .init -f \"example/ex21.json\"\n{\n \"story\": \"${ [partI, 'then', partII]~>$join(' ')}\",\n \"handleRes\": \"${ function($res){$res.ok? $res.json():$res.status?{'status': $res.status}:$res} }\",\n \"call\": \"${function($url){$fetch($url) ~> handleRes}}\",\n \"partI\": \"${ [han, 'piloted the', falcon] ~> $join(' ')}\",\n \"luke\": \"${ call('https://swapi.tech/api/people/?name=luke').result[0].properties.name}\",\n \"xwing\": \"${ call('https://swapi.tech/api/starships/?name=x-wing').result[0].properties.name}\",\n \"partII\": \"${ [luke, 'piloted the', xwing] ~> $join(' ')}\",\n \"han\": \"${ call('https://swapi.tech/api/people/?name=han').result[0].properties.name}\",\n \"falcon\": \"${ call('https://swapi.tech/api/starships/?name=Millennium').result[0].properties.name}\"\n}\n> .svg --port=4042\nServer is running on port 4042\n\"http://localhost:4042\"\n```\nAccess the URL from your web browser to view the SVG diagram.\n\n\n## YAML\nInput can be provided in YAML. YAML is convenient because JSONata prorgrams are often multi-line, and json does not \nsupport text blocks with line returns in a way that is readable. For instance if we compare ex12.json and ex12.yaml, \nwhich is more readable?\n```json\nfalken$ cat ex12.json\n{\n \"url\": \"https://raw.githubusercontent.com/geoffhendrey/jsonataplay/main/games.json\",\n \"selectedGame\": \"${game.selected}\",\n \"respHandler\": \"${ function($res){$res.ok? $res.json():{'error': $res.status}} }\",\n \"game\": \"${ $fetch(url) ~> respHandler ~> |$|{'player':'dlightman'}| }\"\n}\n```\nIn YAML the `respHandler` function can be written as a text block, whereas in JSON it must appear on a single line.\n```bash\nfalken$ cat ex12.yaml\n```\n```yaml\nurl: \"https://raw.githubusercontent.com/geoffhendrey/jsonataplay/main/games.json\"\nselectedGame: \"${game$.selected}\"\nrespHandler$: |\n function($res){\n $res.ok? $res.json():{'error': $res.status}\n }\ngame$: \"$fetch(url) ~> respHandler$ ~> |$|{'player':'dlightman'}|\"\n```\n\nHowever, once a YAML file is parsed with the JavaScript runtime it becomes a JavaScript\nobject. Hence, in the example below a YAML is the input file, but the REPL displays the resulting Javascript object \nusing JSON syntax. As we can see below, loading the yaml file still results in the function being deisplayed\nas it's parsed in-memory JS representation.\n```json lines\n> .init -f \"example/ex12.yaml\"\n{\n \"url\": \"https://raw.githubusercontent.com/geoffhendrey/jsonataplay/main/games.json\",\n \"selectedGame\": \"${game$.selected}\",\n \"respHandler$\": \"function($res){\\n $res.ok? $res.json():{'error': $res.status}\\n}\\n\",\n \"game$\": \"$fetch(url) ~> respHandler$ ~> |$|{'player':'dlightman'}|\"\n}\n```\n## Setting Values in the stated REPL\n\nThe stated REPL also allows you to dynamically set values in your templates, further aiding in debugging and development.\nIn the example below `.set /a/0 100` sets a[0] to 100. The syntax of `/a/0` is [RFC-6901 JSON Pointer](https://datatracker.ietf.org/doc/html/rfc6901).\n\n```json\n> .init -f \"example/ex09.json\"\n{\n \"a\": [\n 0,\n 1,\n \"${ $[0] + $[1] }\"\n ]\n}\n> .set /a/0 100\n{\n \"a\": [\n 100,\n 1,\n 101\n ]\n}\n```\n## Expression Scope\nIndividual JSONata programs are embedded in JSON files between `${..}`. What is the input to the JSONata program? \nThe input, by default, is the object or array that the expression resides in. For instance in the example **above**, you can see that the JSONata `$` variable refers to the array itself. Therefore, expressions like `$[0]`\nrefer to the first element of the array. \n## Rerooting Expressions\nIn Stated templates, one way to declare a JSONata expression is by surrounding it by \"dollars moustaches\".\nE.g `${...some expression...}`. JSONata expressions always have a [context](https://docs.jsonata.org/programming#built-in-variables).\nThe `$` variable always points to the current context. The `$$` variable always points to the input (root context) for an \nexpression.\nIn a Stated template, the root context for an expression is the object in which the expression is contained. For\nExample:\n```json\n> .init -f \"example/context.json\"\n{\n \"a\": {\n \"b\": \"${[c,' and ',$.c,' and ',$$.c,' are the same thing. $ (current context) is /a, the object in which this expression resides']~>$join}\",\n \"c\": \"hello\"\n }\n}\n> .out\n{\n \"a\": {\n \"b\": \"hello and hello and hello are the same thing. $ (current context) is /a, the object in which this expression resides\",\n \"c\": \"hello\"\n }\n}\n```\nNow we will show how we can change the context of an expression using 'rerooting.' Rerooting allows the expression's root\ncontext to be pointed anywhere in the json document.\nIn the example below, consider `greeting & ', ' & player1'`. We want `player1` to refer to the content at json pointer `/player1` (the field named 'player1' at the root of the document). \nBut our expression `greeting & ', ' & player1` is located deep in the document at `/dialog/partI`. So how can we cause \nthe root of the document to be the context for the JSONata expression `greeting & ', ' & player1`? \nYou can reroot an expression in a different part of the document using relative rooting `../${