It's designed to be used in ACL (Access Control List) systems, where you need to check if a user has access to a resource.

(@record.published || @record.owner == @req.user.id) // Normal case
|| // Or operator
(@req.user.role == 'admin' || @req.user.id in @record.granted) // Special case

Let's break it down:

• @req.user.role == 'admin': Check if the user has the role of admin.
• @req.user.id in @record.granted: Check if the user's id is in the granted list of the record.
• @record.published: Check if the record is published.
• @record.owner == @req.user.id: Check if the record's owner is the user.

The above example is a simple ACL system that checks if the user has access to a record.

More language details can be found in LANG.md.

• json (enabled by default)
• yaml
• toml

At least one input format feature must be enabled. The default configuration enables json.

// Parse expr
let expr = "@req.user.name in 'foobar' && @files.0.published == true";
let expr = Expr::try_from(expr)?;

// Construct context
let ctx_names = expr.requested_ctx(); // ["req", "files"]
// You can construct the context indeed, but we use json! for simplicity
let ctx = json!({
    "req": {
        "user": "foo"
    },
    "files": [
        {
            "name": "file1",
            "published": true
        }
    ]
});

// Eval
let result = expr.eval(ctx.into())?; // Val::Bool(true)
match result {
    Val::Bool(b) => {
        assert!(b);
    }
    _ => {
        panic!("unexpected result");
    }
}

Apache-2.0 lollipopkit