Scope Proposal

[TotalTechGeek]

Background

One undefined behavior in JSON Logic is how you should access context from outer scopes when working with scope introduced by an iterator.

This prevents you from using filter using an item stored in your context, or adding the index / a value from your context within a map statement.

See:

• filter does not work with the second parameter as var json-logic-engine#28
• Data is not used by "some" jwadhams/json-logic-js#48
• use the data "var" in side "filter" jwadhams/json-logic-js#61
• Referencing data values within a map jwadhams/json-logic-js#124

Suggestion

The json-logic-engine implementation resolves it in the following way:

What if we use directory style traversal to allow folks to reference outer scopes? ../ would go up a layer.

So to reference the index of an iterator, you'd reach into the iterator's scope with ../index.

And to reference the context above the iterator, to fetch a property like name you'd climb up two levels, ../../name.

Proposed Test Suite

[
    "A proposal for handling scopes",
    {
        "description": "Map can add each number to index",
        "rule": {
            "map": [
                { "var": "numbers" },
                { "+": [{ "var": "../index" }, { "var": "" }]}
            ]
        },
        "data": { "numbers": [1,2,3] },
        "result": [1,3,5]
    },
    {
        "description": "Map can add each number to value from context",
        "rule": {
            "map": [
                { "var": "numbers" },
                { "+": [{ "var": "../../value" }, { "var": "" }]}
            ]
        },
        "data": { "numbers": [1,2,3], "value": 10 },
        "result": [11,12,13]
    },
    {
        "description": "Filter can use parent context to filter",
        "rule": {
            "filter": [
                { "var": "people" },
                { "===": [{ "var": "department" }, { "var": "../../department" }] }
            ]
        },
        "data": {
            "department": "Engineering",
            "people": [
                { "name": "Jay Ortiz", "department": "Engineering" },
                { "name": "Louisa Hall", "department": "Sales" },
                { "name": "Kyle Carlson", "department": "Sales" },
                { "name": "Grace Ortiz", "department": "Engineering" },
                { "name": "Isabelle Harrington", "department": "Marketing" },
                { "name": "Harold Moore", "department": "Sales" },
                { "name": "Clarence Schultz", "department": "Sales" },
                { "name": "Jesse Keller", "department": "Engineering" },
                { "name": "Phillip Holland", "department": "Marketing" },
                { "name": "Mason Sullivan", "department": "Engineering" }
            ]
        },
        "result": [
            { "name": "Jay Ortiz", "department": "Engineering" },
            { "name": "Grace Ortiz", "department": "Engineering" },
            { "name": "Jesse Keller", "department": "Engineering" },
            { "name": "Mason Sullivan", "department": "Engineering" }
        ]
    },
    "The specification below depends upon escaping from another proposal",
    {
        "description": "Access an escaped key from above",
        "rule": { 
            "map": [
                { "var": "arr" }, 
                { "+": [{ "var": "../../\\.\\./" }, { "var": "../../..\\/" }]}
            ] 
        },
        "data": { "arr": [1,2,3], "../": 10, "": { "": { "/": 7 }} },
        "result": [17,17,17]
    }
]

[TotalTechGeek]

I believe I'll be closing this proposal and introducing a new one, based on misc discussions we've had in different threads.