1 files changed, 33 insertions, 1 deletions
diff --git a/src/pipeline.rs b/src/pipeline.rs
index cba046f..cce3e31 100644
--- a/src/pipeline.rs
+++ b/src/pipeline.rs
@@ -78,12 +78,33 @@ impl Root {
     }
 }
 
+// address nodes by their role relative to their parent
+enum NixSyntaxRole {
+    Argument,
+    Function,
+    Attribute,
+    // TODO
+}
+
+impl NixSyntaxRole {
+    fn from_str(from: &str) -> Option<NixSyntaxRole> {
+        use NixSyntaxRole::*;
+        Some(match from {
+            "Argument" => Argument,
+            "Function" => Function,
+            "Attribute" => Attribute,
+            _ => return None
+        })
+    }
+}
+
 enum Op {
     Down,
     DownRecursive,
     Up,
     UpRecursive,
     NixSyntaxNode(rnix::SyntaxKind),
+    NixSyntaxRole(NixSyntaxRole),
     Named(String)
 }
 
@@ -100,7 +121,11 @@ impl Atom {
             "Inherit" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_INHERIT),
             "String" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_STRING),
             // TODO other syntax nodes
-            name => Op::Named(name.to_owned()),
+            name => if let Some(role) = NixSyntaxRole::from_str(name) {
+                Op::NixSyntaxRole(role)
+            } else {
+                Op::Named(name.to_owned())
+            },
         };
         Some(op)
     }
@@ -129,6 +154,13 @@ impl Atom {
             Some(Op::UpRecursive) => Box::new(acc.map(|s| s.ancestors()).flatten()),
             // TODO: how to select roles relative to previous node?
             Some(Op::NixSyntaxNode(kind)) => Box::new(acc.filter(move |s| s.kind() == kind)),
+            Some(Op::NixSyntaxRole(role)) => {use NixSyntaxRole::*; match role {
+                Argument => Box::new(acc.filter_map(move |s| match_ast! { match s {
+                   ast::Apply(value) => value.argument().map(|s| s.syntax().to_owned()),
+                    _ => None
+                }})),
+                _ => todo!()
+            }}
             Some(Op::Named(name)) =>
                 Box::new(acc
                 .filter(move |node| match_ast! { match node {