some restructuring, arg handling, re-enable batchmode

6 files changed, 567 insertions, 262 deletions

diff --git a/Cargo.lock b/Cargo.lock
index bf58e1f..eac2997 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -12,12 +12,54 @@ dependencies = [
 ]
 
 [[package]]
+name = "anstream"
+version = "0.6.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d96bd03f33fe50a863e394ee9718a706f988b9079b20c3784fb726e7678b62fb"
+dependencies = [
+ "anstyle",
+ "anstyle-parse",
+ "anstyle-query",
+ "anstyle-wincon",
+ "colorchoice",
+ "utf8parse",
+]
+
+[[package]]
 name = "anstyle"
 version = "1.0.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8901269c6307e8d93993578286ac0edf7f195079ffff5ebdeea6a59ffb7e36bc"
 
 [[package]]
+name = "anstyle-parse"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c75ac65da39e5fe5ab759307499ddad880d724eed2f6ce5b5e8a26f4f387928c"
+dependencies = [
+ "utf8parse",
+]
+
+[[package]]
+name = "anstyle-query"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e28923312444cdd728e4738b3f9c9cac739500909bb3d3c94b43551b16517648"
+dependencies = [
+ "windows-sys",
+]
+
+[[package]]
+name = "anstyle-wincon"
+version = "3.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1cd54b81ec8d6180e24654d0b371ad22fc3dd083b6ff8ba325b72e00c87660a7"
+dependencies = [
+ "anstyle",
+ "windows-sys",
+]
+
+[[package]]
 name = "anyhow"
 version = "1.0.81"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -36,6 +78,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "90bc066a67923782aa8515dbaea16946c5bcc5addbd668bb80af688e53e548a0"
 dependencies = [
  "clap_builder",
+ "clap_derive",
 ]
 
 [[package]]
@@ -44,8 +87,22 @@ version = "4.5.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ae129e2e766ae0ec03484e609954119f123cc1fe650337e155d03b022f24f7b4"
 dependencies = [
+ "anstream",
  "anstyle",
  "clap_lex",
+ "strsim",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.5.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "528131438037fd55894f62d6e9f068b8f45ac57ffa77517819645d10aed04f64"
+dependencies = [
+ "heck",
+ "proc-macro2",
+ "quote",
+ "syn",
 ]
 
 [[package]]
@@ -55,6 +112,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "98cc8fbded0c607b7ba9dd60cd98df59af97e84d24e49c8557331cfc26d301ce"
 
 [[package]]
+name = "colorchoice"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
+
+[[package]]
 name = "countme"
 version = "3.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -73,6 +136,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "290f1a1d9242c78d09ce40a5e87e7554ee637af1351968159f4952f028f75604"
 
 [[package]]
+name = "heck"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
+
+[[package]]
 name = "hermit-abi"
 version = "0.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -262,6 +331,12 @@ dependencies = [
 ]
 
 [[package]]
+name = "strsim"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7da8b5736845d9f2fcb837ea5d9e2628564b3b043a70948a3f0b778838c5fb4f"
+
+[[package]]
 name = "syn"
 version = "2.0.53"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -292,3 +367,75 @@ name = "unicode-ident"
 version = "1.0.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3354b9ac3fae1ff6755cb6db53683adb661634f67557942dea4facebec0fee4b"
+
+[[package]]
+name = "utf8parse"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "711b9620af191e0cdc7468a8d14e709c3dcdb115b36f838e601583af800a370a"
+
+[[package]]
+name = "windows-sys"
+version = "0.52.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "282be5f36a8ce781fad8c8ae18fa3f9beff57ec1b52cb3de0789201425d9a33d"
+dependencies = [
+ "windows-targets",
+]
+
+[[package]]
+name = "windows-targets"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7dd37b7e5ab9018759f893a1952c9420d060016fc19a472b4bb20d1bdd694d1b"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bcf46cf4c365c6f2d1cc93ce535f2c8b244591df96ceee75d8e83deb70a9cac9"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da9f259dd3bcf6990b55bffd094c4f7235817ba4ceebde8e6d11cd0c5633b675"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b474d8268f99e0995f25b9f095bc7434632601028cf86590aea5c8a5cb7801d3"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1515e9a29e5bed743cb4415a9ecf5dfca648ce85ee42e15873c3cd8610ff8e02"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5eee091590e89cc02ad514ffe3ead9eb6b660aedca2183455434b93546371a03"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77ca79f2451b49fa9e2af39f0747fe999fcda4f5e241b2898624dca97a1f2177"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.52.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32b752e52a2da0ddfbdbcc6fceadfeede4c939ed16d13e648833a61dfb611ed8"
diff --git a/Cargo.toml b/Cargo.toml
index 4705207..12517b8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -16,4 +16,4 @@ serde_json = "1.0"
 serde = { version = "1.0", features = ["derive"] }
 itertools = "0.12.1"
 m_lexer = "0.0.4"
-clap = { version = "4.5", features = [ "cargo", "help", "std" ], default-features = false }
+clap = { version = "4.5", features = [ "derive" ] }
diff --git a/src/batchmode.rs b/src/batchmode.rs
index 8398bce..84b0dff 100644
--- a/src/batchmode.rs
+++ b/src/batchmode.rs
@@ -1,30 +1,43 @@
 use std::{path::PathBuf, fs, sync::{Arc, Mutex}};
+use rowan::ast::AstNode;
 use threadpool::ThreadPool;
 
-use crate::status_reporter::*;
+use crate::{status_reporter::*, queries::{SyntaxNode, Parse}, parse_nexp, apply_changes};
 
-// TODO: make this usable
-// (this module just here to keep old code around for a bit)
-pub enum Task {}
 
 #[allow(unreachable_code, unused)]
-pub fn batchmode(tasks: Vec<(PathBuf, Task)>) {
+pub fn batchmode(tasks: Vec<PathBuf>, query: Parse, debug: bool) {
 
+    fn do_task(path: PathBuf, query: Parse, debug: bool) -> anyhow::Result<(PathBuf, Option<String>)> {
+
+        let (content, nexp) = match parse_nexp(&path) {
+            Err(e) => {
+                anyhow::bail!("could not parse file {path:?}")
+            },
+            Ok(exp) => exp
+        };
+
+        let (changes, _) = query.apply(&content, nexp.syntax().clone())?;
+
+        let changed = apply_changes(&content, changes, debug);
+
+        Ok((path, if changed != content { Some(changed) } else { None }))
+    }
     let pool = ThreadPool::new(16);
 
     let results = Arc::new(Mutex::new(vec![]));
     let printer = Arc::new(StatusReport::new(tasks.len(), tasks.len()));
 
-    for (path, task) in tasks {
+    for path in tasks {
         pool.execute({
             let results = Arc::clone(&results);
             let printer = Arc::clone(&printer);
+            let query = query.clone();
 
             move || {
                 printer.enter_file(&format!("{path:?}"));
 
-                let result: anyhow::Result<(PathBuf, String)> = todo!();
-
+                let result = do_task(path, query, debug);
                 results.lock().unwrap().push(result);
             }
         });
@@ -35,18 +48,20 @@ pub fn batchmode(tasks: Vec<(PathBuf, Task)>) {
     println!("\n\nSummary:");
     let mut c_errors = 0;
     let mut c_total = 0;
+    let mut c_changes = 0;
     for r in results.lock().unwrap().iter() {
         match r {
             Err(e) => {
                 println!(" {}", e);
                 c_errors += 1;
             },
+            Ok((_, Some(_))) => c_changes += 1,
             _ => ()
         }
         c_total += 1;
     }
 
-    println!("\n  ({c_total} sites total, {c_errors} errors, generated {} edits)", c_total - c_errors);
+    println!("\n  ({c_total} sites total, {c_errors} errors, generated {} edits)", c_changes);
 
     let edits: Vec<_> = Arc::into_inner(results).unwrap().into_inner().unwrap()
         .into_iter()
@@ -55,7 +70,8 @@ pub fn batchmode(tasks: Vec<(PathBuf, Task)>) {
 
     println!("applying changes ...");
     for (filename, content) in edits {
-        fs::write(&filename, content.as_bytes()).unwrap();
-        // println!("{}", content);
+        if let Some(content) = content {
+            fs::write(&filename, content.as_bytes()).unwrap();
+        }
     }
 }
diff --git a/src/main.rs b/src/main.rs
index a09f4ef..2bc44ab 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,7 @@
 use std::{path::PathBuf, fs, process::exit};
-use rowan::{ast::AstNode, TextSize};
-use clap::{arg, command, value_parser};
+use pipeline::{Change, ChangeKind};
+use rowan::{ast::AstNode, TextSize, NodeOrToken};
+use clap::{arg, Parser};
 
 #[allow(dead_code)]
 mod queries;
@@ -9,6 +10,19 @@ mod status_reporter;
 mod batchmode;
 #[allow(dead_code)]
 mod util;
+#[allow(dead_code)]
+mod pipeline;
+
+
+#[derive(clap::Parser)]
+struct Args {
+    query: String,
+    path: Vec<PathBuf>,
+    #[arg(short, long)]
+    debug: bool,
+    #[arg(long)]
+    batchmode: bool
+}
 
 
 fn parse_nexp(path: &PathBuf) -> anyhow::Result<(String, rnix::Root)> {
@@ -23,24 +37,9 @@ fn parse_nexp(path: &PathBuf) -> anyhow::Result<(String, rnix::Root)> {
 
 fn main() {
 
-    let matches = command!()
-        .arg(arg!(--batchmode "run in batch mode")
-             .required(false)
-        )
-        .arg(arg!([query] "query to run")
-             .required(true))
-        .arg(arg!([file] "file to operate on")
-            .required(true)
-             .value_parser(value_parser!(PathBuf))
-        )
-        .arg(arg!(--edit <operation> "what to do")
-        .required(false))
-        .get_matches();
-
-    let query_string = matches.get_one::<String>("query").unwrap();
-    let files = matches.get_one::<PathBuf>("file").unwrap();
-
-    let parse = queries::parse(query_string);
+    let args = Args::parse();
+
+    let parse = queries::parse(&args.query);
     if parse.errors.len() != 0 {
         eprintln!(
             "syntax {}: \n  {}",
@@ -50,61 +49,144 @@ fn main() {
         exit(1);
     }
 
-    let (content, nexp) = match parse_nexp(files) {
-        Err(e) => {
-            eprintln!("could not parse file: {e}");
-            exit(2);
-        },
-        Ok(exp) => exp
-    };
-
     // println!("{nexp:#?}");
 
-    let results = parse.apply(&content, nexp.syntax().clone()).unwrap();
-
+    if args.batchmode {
+        batchmode::batchmode(args.path, parse, args.debug);
+    } else {
+        let (content, nexp) = match parse_nexp(&args.path[0]) {
+            Err(e) => {
+                eprintln!("could not parse file: {e}");
+                exit(2);
+            },
+            Ok(exp) => exp
+        };
+
+        let (changes, results) = parse.apply(&content, nexp.syntax().clone()).unwrap();
+
+        if args.debug {
+            println!("{changes:?}");
+        }
 
-    if let Some(op) = matches.get_one::<String>("edit") {
-        match &op[..] {
-            "remove" => {
-                let new = remove_nodes(content, &results);
-                println!("{new}");
+        if changes.len() == 0 {
+            for result in results {
+                println!("{result}");
             }
-            _ => ()
+        } else {
+            let changed = apply_changes(&content, changes, args.debug);
+
+            println!("{changed}");
         }
-    } else {
-        for result in &results {
-            println!("{result}");
+    }
+}
+
+
+fn apply_changes(content: &str, mut changes: Vec<Change>, debug: bool) -> String {
+    let mut last_pos = 0;
+    let mut ncontent = String::new();
+
+    changes.sort_by_key(|change| change.node.text_range().start());
+
+    for change in changes {
+        match change.kind {
+            ChangeKind::Remove => {
+                let (before, after) = remove_node(&change.node);
+                if last_pos > before { continue }
+                ncontent += &content[last_pos..before];
+                if debug {
+                    println!("removing: {}", &content[before..after])
+                }
+                last_pos = after;
+            }
+            ChangeKind::Keep => {
+                // let (before, after) = surrounding_whitespace(&change.node);
+                let (before, after) = (change.node.text_range().start().into(), change.node.text_range().end().into());
+                if debug {
+                    println!("keeping: {}", &content[before..after])
+                };
+                ncontent += &content[before..after];
+                // last_pos = after;
+            }
         }
     }
 
+    ncontent += &content[last_pos..];
 
+    ncontent
 }
 
-fn remove_nodes(content: String, results: &Vec<rnix::SyntaxNode>) -> String {
-
-    assert!(results.len() == 1);
+#[allow(unused)]
+fn surrounding_whitespace(node: &rnix::SyntaxNode) -> (usize, usize) {
+    let before = node
+        .prev_sibling_or_token()
+        .filter(|n| n.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE)
+        .map(|n| n.text_range().start().into())
+        .unwrap_or_else(|| node.text_range().start().into());
+    let after = node
+        .next_sibling_or_token()
+        .filter(|n| n.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE)
+        .map(|n| n.text_range().end().into())
+        .unwrap_or_else(|| node.text_range().end().into());
+
+    (before, after)
+}
 
-    let span = &results[0];
 
-    let (before, after) = match (span.prev_sibling_or_token(), span.next_sibling_or_token()) {
-        (Some(prev), Some(next))
-            if prev.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE
-              && next.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE
-        => {
-            if prev.to_string().lines().count() < next.to_string().lines().count() {
-                (prev.text_range().len(), TextSize::new(0))
-            } else {
-                (TextSize::new(0), next.text_range().len())
+fn remove_node(span: &rnix::SyntaxNode) -> (usize, usize) {
+
+    // TODO: how to remove brackets around the node?
+
+    fn eat_to_bracket(node: &rnix::SyntaxNode, backwards: bool) -> (TextSize, usize) {
+        let mut span = NodeOrToken::Node(node.clone());
+        let mut bracket = span.clone();
+        let mut brackets = 0;
+        loop {
+            match if backwards { span.prev_sibling_or_token() } else { span.next_sibling_or_token() } {
+                Some(NodeOrToken::Token(t)) => match t.kind() {
+                    rnix::SyntaxKind::TOKEN_WHITESPACE => span = NodeOrToken::Token(t),
+                    rnix::SyntaxKind::TOKEN_L_PAREN if backwards => {
+                        span = NodeOrToken::Token(t);
+                        bracket = span.clone();
+                        brackets += 1;
+                    },
+                    rnix::SyntaxKind::TOKEN_R_PAREN if !backwards => {
+                        span = NodeOrToken::Token(t);
+                        bracket = span.clone();
+                        brackets += 1;
+                    },
+                    _ => break,
+                },
+                _ => break,
             }
         }
-        _ => (TextSize::default(),TextSize::default())
+        (if backwards { bracket.text_range().start() } else { bracket.text_range().end() }, brackets)
+    }
+
+    let (before, after) = match (eat_to_bracket(span, true), eat_to_bracket(span, false)) {
+        ((before, n1), (after, n2)) if n1 == n2 && n1 != 0 => (before.into(), after.into()),
+        _ => match (span.prev_sibling_or_token(), span.next_sibling_or_token()) {
+            (Some(prev), Some(next))
+                if prev.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE
+                && next.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE
+                => {
+                    if prev.to_string().lines().count() < next.to_string().lines().count() {
+                        (Into::<usize>::into(span.text_range().start() - prev.text_range().len()) + previous_indentation(&span).unwrap_or(0)
+                         , Into::<usize>::into(span.text_range().end()) + next_indentation(&span).unwrap_or(0))
+                    } else {
+                        (Into::<usize>::into(span.text_range().start()) - previous_indentation(&span).unwrap_or(0),
+                         Into::<usize>::into(span.text_range().end() + next.text_range().len()) - next_indentation(&span).unwrap_or(0))
+                    }
+                }
+            _ => (span.text_range().start().into(), span.text_range().end().into())
+        }
     };
 
-    String::new()
-        + &content[..Into::<usize>::into(span.text_range().start() - before) - previous_indentation(span).unwrap_or(0)]
-        + &content[(span.text_range().end() + after).into()..]
-}
 
+    (before, after)
+    // ( Into::<usize>::into(span.text_range().start()) - before
+    // , Into::<usize>::into(span.text_range().end()) + after
+    // )
+}
 
 
 fn previous_indentation(node: &rnix::SyntaxNode) -> Option<usize> {
@@ -116,3 +198,13 @@ fn previous_indentation(node: &rnix::SyntaxNode) -> Option<usize> {
         None
     }
 }
+
+fn next_indentation(node: &rnix::SyntaxNode) -> Option<usize> {
+    let whitespace_token = node.next_sibling_or_token()?;
+
+    if whitespace_token.kind() == rnix::SyntaxKind::TOKEN_WHITESPACE {
+        Some(whitespace_token.to_string().lines().last().unwrap().len())
+    } else {
+        None
+    }
+}
diff --git a/src/pipeline.rs b/src/pipeline.rs
new file mode 100644
index 0000000..cba046f
--- /dev/null
+++ b/src/pipeline.rs
@@ -0,0 +1,203 @@
+
+use itertools::Itertools;
+use rnix::{match_ast, ast};
+use rowan::ast::AstNode;
+use crate::queries::*;
+use crate::queries::SyntaxKind::*;
+
+#[derive(Debug)]
+pub struct Change {
+    pub node: rnix::SyntaxNode,
+    pub kind: ChangeKind
+}
+
+#[derive(Copy, Clone, Debug)]
+pub enum ChangeKind {
+    Remove,
+    Keep
+}
+
+type NixExprs = Box<dyn Iterator<Item = rnix::SyntaxNode>>;
+type Pipe = (Vec<Change>, NixExprs);
+
+macro_rules! ast_node {
+    ($ast:ident, $kind:ident) => {
+        #[derive(PartialEq, Eq, Hash)]
+        #[repr(transparent)]
+        struct $ast(SyntaxNode);
+        impl $ast {
+            #[allow(unused)]
+            fn cast(node: SyntaxNode) -> Option<Self> {
+                if node.kind() == $kind {
+                    Some(Self(node))
+                } else {
+                    None
+                }
+            }
+        }
+    };
+}
+
+ast_node!(Root, ROOT);
+ast_node!(Atom, ATOM);
+ast_node!(List, LIST);
+
+#[derive(PartialEq, Eq, Hash, Debug)]
+#[repr(transparent)]
+struct Qexp(SyntaxNode);
+
+enum QexpKind {
+    Atom(Atom),
+    List(List),
+}
+
+impl Qexp {
+    fn cast(node: SyntaxNode) -> Option<Self> {
+        if Atom::cast(node.clone()).is_some() || List::cast(node.clone()).is_some() {
+            Some(Qexp(node))
+        } else {
+            None
+        }
+    }
+
+    fn kind(&self) -> QexpKind {
+        Atom::cast(self.0.clone())
+            .map(QexpKind::Atom)
+            .or_else(|| List::cast(self.0.clone()).map(QexpKind::List))
+            .unwrap()
+    }
+
+    fn apply(&self, _acc: Pipe) -> Pipe {
+        todo!()
+    }
+}
+
+impl Root {
+    fn qexps(&self) -> impl Iterator<Item = Qexp> + '_ {
+        self.0.children().filter_map(Qexp::cast)
+    }
+}
+
+enum Op {
+    Down,
+    DownRecursive,
+    Up,
+    UpRecursive,
+    NixSyntaxNode(rnix::SyntaxKind),
+    Named(String)
+}
+
+impl Atom {
+    fn eval(&self) -> Option<i64> {
+        self.text().parse().ok()
+    }
+    fn as_op(&self) -> Option<Op> {
+        let op = match self.text().as_str() {
+            ">" => Op::Down,
+            ">>" => Op::DownRecursive,
+            "<" => Op::Up,
+            "<<" => Op::UpRecursive,
+            "Inherit" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_INHERIT),
+            "String" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_STRING),
+            // TODO other syntax nodes
+            name => Op::Named(name.to_owned()),
+        };
+        Some(op)
+    }
+    fn as_change(&self) -> Option<ChangeKind> {
+        let change = match self.text().as_str() {
+            "remove" => ChangeKind::Remove,
+            "keep" => ChangeKind::Keep,
+            _ => return None
+        };
+        Some(change)
+    }
+    fn iter_args(&self) -> impl Iterator<Item = Atom>  {
+        self.0.children().find_map(List::cast).into_iter().map(|arglist| arglist.iter()).flatten()
+    }
+    fn text(&self) -> String {
+        match self.0.green().children().next() {
+            Some(rowan::NodeOrToken::Token(token)) => token.text().to_string(),
+            _ => unreachable!(),
+        }
+    }
+    fn apply(&self, (mut changes, acc): Pipe) -> Pipe {
+        let mut acc: NixExprs = match self.as_op() {
+            Some(Op::Down) => Box::new(acc.map(|s| s.children()).flatten()),
+            Some(Op::DownRecursive) => Box::new(acc.map(|s| s.descendants()).flatten()),
+            Some(Op::Up) => Box::new(acc.filter_map(|s| s.parent())),
+            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::Named(name)) =>
+                Box::new(acc
+                .filter(move |node| match_ast! { match node {
+                    ast::AttrpathValue(value) => {
+                        name == value.attrpath().unwrap().to_string()
+                    },
+                    ast::Apply(value) => {
+                        // TODO: special case lambda = NODE_SELECT here?
+                        name == value.lambda().unwrap().to_string()
+                    },
+                    // TODO: this is difficult — I want to use free-form names
+                    // to select things below, too, but that might not always be
+                    // possible. perhaps it is possible to skip over descendants?
+                    ast::Ident(value) => {
+                        name == value.to_string()
+                    },
+                    _ => false
+                }})),
+            _ => todo!()
+        };
+
+        if let Ok(arg) = self.iter_args().exactly_one() {
+            if let Some(change) = arg.as_change() {
+                let (mut nchanges, nacc): (Vec<_>, Vec<_>) = acc
+                    .map(|node| (Change { node: node.clone(), kind: change }, node))
+                    .unzip();
+                acc = Box::new(nacc.into_iter());
+                changes.append(&mut nchanges);
+            }
+        }
+
+        (changes, acc)
+    }
+}
+
+impl List {
+    fn sexps(&self) -> impl Iterator<Item = Qexp> + '_ {
+        self.0.children().filter_map(Qexp::cast)
+    }
+
+    fn iter(&self) -> impl Iterator<Item = Atom> {
+        self.0.children().filter_map(Atom::cast)
+    }
+}
+
+
+
+impl Parse {
+    fn root(&self) -> Root {
+        Root::cast(self.syntax()).unwrap()
+    }
+
+    pub fn apply(&self, _content: &str, nexp: rnix::SyntaxNode) -> anyhow::Result<(Vec<Change>, Vec<rnix::SyntaxNode>)> {
+
+        let mut pipe: Pipe = (Vec::new(), Box::new(std::iter::once(nexp)));
+
+        for qexp in self.root().qexps() {
+            match qexp.kind() {
+                QexpKind::Atom(filter) => {
+                    pipe = filter.apply(pipe);
+                }
+                _ => panic!("???")
+            }
+        }
+
+        // let results =
+        //     acc.map(|node| content[node.text_range().start().into()..node.text_range().end().into()].to_owned())
+        //     .collect();
+
+        Ok((pipe.0, pipe.1.collect()))
+    }
+}
diff --git a/src/queries.rs b/src/queries.rs
index b07224a..c1e16df 100644
--- a/src/queries.rs
+++ b/src/queries.rs
@@ -1,9 +1,43 @@
 // this is mostly based on the s-exp tutorial
 // https://github.com/rust-analyzer/rowan/blob/master/examples/s_expressions.rs
 
-use rnix::{match_ast, ast};
-use rowan::{GreenNode, GreenNodeBuilder, ast::AstNode};
+use rowan::{GreenNode, GreenNodeBuilder};
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[allow(non_camel_case_types)]
+#[repr(u16)]
+pub enum SyntaxKind {
+    L_BRACKET = 0, // '['
+    R_BRACKET,     // ']'
+    WORD,          // 'Attrset', 'meta', '.', '>', ...
+    WHITESPACE,    // whitespaces is explicit
+    ERROR,         // as well as errors
+
+    // composite nodes
+    LIST, // `[..]`
+    ATOM, // wraps WORD
+    ROOT, // top-level (a complete query)
+}
+use SyntaxKind::*;
+
+impl From<SyntaxKind> for rowan::SyntaxKind {
+    fn from(kind: SyntaxKind) -> Self {
+        Self(kind as u16)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum QueryLang {}
+impl rowan::Language for QueryLang {
+    type Kind = SyntaxKind;
+    fn kind_from_raw(raw: rowan::SyntaxKind) -> Self::Kind {
+        assert!(raw.0 <= ROOT as u16);
+        unsafe { std::mem::transmute::<u16, SyntaxKind>(raw.0) }
+    }
+    fn kind_to_raw(kind: Self::Kind) -> rowan::SyntaxKind {
+        kind.into()
+    }
+}
 
 fn lex(text: &str) -> Vec<(SyntaxKind, String)> {
     fn tok(t: SyntaxKind) -> m_lexer::TokenKind {
@@ -43,42 +77,7 @@ fn lex(text: &str) -> Vec<(SyntaxKind, String)> {
 }
 
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-#[allow(non_camel_case_types)]
-#[repr(u16)]
-enum SyntaxKind {
-    L_BRACKET = 0, // '['
-    R_BRACKET,     // ']'
-    WORD,          // 'Attrset', 'meta', '.', '>', ...
-    WHITESPACE,    // whitespaces is explicit
-    ERROR,         // as well as errors
-
-    // composite nodes
-    LIST, // `[..]`
-    ATOM, // wraps WORD
-    ROOT, // top-level (a complete query)
-}
-use SyntaxKind::*;
-
-impl From<SyntaxKind> for rowan::SyntaxKind {
-    fn from(kind: SyntaxKind) -> Self {
-        Self(kind as u16)
-    }
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
-enum Lang {}
-impl rowan::Language for Lang {
-    type Kind = SyntaxKind;
-    fn kind_from_raw(raw: rowan::SyntaxKind) -> Self::Kind {
-        assert!(raw.0 <= ROOT as u16);
-        unsafe { std::mem::transmute::<u16, SyntaxKind>(raw.0) }
-    }
-    fn kind_to_raw(kind: Self::Kind) -> rowan::SyntaxKind {
-        kind.into()
-    }
-}
-
+#[derive(Clone)]
 pub struct Parse {
     pub green_node: GreenNode,
     pub errors: Vec<String>,
@@ -207,14 +206,14 @@ pub fn parse(text: &str) -> Parse {
 /// but it contains parent pointers, offsets, and
 /// has identity semantics.
 
-type SyntaxNode = rowan::SyntaxNode<Lang>;
+pub type SyntaxNode = rowan::SyntaxNode<QueryLang>;
 #[allow(unused)]
-type SyntaxToken = rowan::SyntaxToken<Lang>;
+type SyntaxToken = rowan::SyntaxToken<QueryLang>;
 #[allow(unused)]
 type SyntaxElement = rowan::NodeOrToken<SyntaxNode, SyntaxToken>;
 
 impl Parse {
-    fn syntax(&self) -> SyntaxNode {
+    pub fn syntax(&self) -> SyntaxNode {
         SyntaxNode::new_root(self.green_node.clone())
     }
 }
@@ -257,155 +256,3 @@ fn test_parser() {
 
 
 
-type NixExprs = Box<dyn Iterator<Item = rnix::SyntaxNode>>;
-
-macro_rules! ast_node {
-    ($ast:ident, $kind:ident) => {
-        #[derive(PartialEq, Eq, Hash)]
-        #[repr(transparent)]
-        struct $ast(SyntaxNode);
-        impl $ast {
-            #[allow(unused)]
-            fn cast(node: SyntaxNode) -> Option<Self> {
-                if node.kind() == $kind {
-                    Some(Self(node))
-                } else {
-                    None
-                }
-            }
-        }
-    };
-}
-
-ast_node!(Root, ROOT);
-ast_node!(Atom, ATOM);
-ast_node!(List, LIST);
-
-// Sexp is slightly different, so let's do it by hand.
-#[derive(PartialEq, Eq, Hash, Debug)]
-#[repr(transparent)]
-struct Qexp(SyntaxNode);
-
-enum QexpKind {
-    Atom(Atom),
-    List(List),
-}
-
-impl Qexp {
-    fn cast(node: SyntaxNode) -> Option<Self> {
-        if Atom::cast(node.clone()).is_some() || List::cast(node.clone()).is_some() {
-            Some(Qexp(node))
-        } else {
-            None
-        }
-    }
-
-    fn kind(&self) -> QexpKind {
-        Atom::cast(self.0.clone())
-            .map(QexpKind::Atom)
-            .or_else(|| List::cast(self.0.clone()).map(QexpKind::List))
-            .unwrap()
-    }
-
-    fn apply(&self, _acc: NixExprs) -> NixExprs {
-        todo!()
-    }
-}
-
-// Let's enhance AST nodes with ancillary functions and
-// eval.
-impl Root {
-    fn qexps(&self) -> impl Iterator<Item = Qexp> + '_ {
-        self.0.children().filter_map(Qexp::cast)
-    }
-}
-
-enum Op {
-    Down,
-    DownRecursive,
-    Up,
-    UpRecursive,
-    Named(String)
-}
-
-impl Atom {
-    fn eval(&self) -> Option<i64> {
-        self.text().parse().ok()
-    }
-    fn as_op(&self) -> Option<Op> {
-        let op = match self.text().as_str() {
-            ">" => Op::Down,
-            ">>" => Op::DownRecursive,
-            "<" => Op::Up,
-            "<<" => Op::UpRecursive,
-            name => Op::Named(name.to_owned()),
-        };
-        Some(op)
-    }
-    fn text(&self) -> String {
-        match self.0.green().children().next() {
-            Some(rowan::NodeOrToken::Token(token)) => token.text().to_string(),
-            _ => unreachable!(),
-        }
-    }
-    fn apply(&self, acc: NixExprs) -> NixExprs {
-        match self.as_op() {
-            Some(Op::Down) => Box::new(acc.map(|s| s.children()).flatten()),
-            Some(Op::DownRecursive) => Box::new(acc.map(|s| s.descendants()).flatten()),
-            Some(Op::Up) => Box::new(acc.filter_map(|s| s.parent())),
-            Some(Op::UpRecursive) => Box::new(acc.map(|s| s.ancestors()).flatten()),
-            Some(Op::Named(name)) =>
-                Box::new(acc
-                .filter(move |node| match_ast! { match node {
-                    ast::AttrpathValue(value) => {
-                        name == value.attrpath().unwrap().to_string()
-                    },
-                    ast::Apply(value) => {
-                        // TODO: special case lambda = NODE_SELECT here?
-                        name == value.lambda().unwrap().to_string()
-                    },
-                    // TODO: this is difficult — I want to use free-form names
-                    // to select things below, too, but that might not always be
-                    // possible
-                    ast::Ident(value) => {
-                        name == value.to_string()
-                    },
-                    _ => false
-                }})),
-            _ => todo!()
-        }
-    }
-}
-
-impl List {
-    fn sexps(&self) -> impl Iterator<Item = Qexp> + '_ {
-        self.0.children().filter_map(Qexp::cast)
-    }
-}
-
-
-impl Parse {
-    fn root(&self) -> Root {
-        Root::cast(self.syntax()).unwrap()
-    }
-
-    pub fn apply(&self, _content: &str, nexp: rnix::SyntaxNode) -> anyhow::Result<Vec<rnix::SyntaxNode>> {
-
-        let mut acc: NixExprs = Box::new(std::iter::once(nexp));
-
-        for qexp in self.root().qexps() {
-            match qexp.kind() {
-                QexpKind::Atom(filter) => {
-                    acc = filter.apply(acc);
-                }
-                _ => panic!("???")
-            }
-        }
-
-        // let results =
-        //     acc.map(|node| content[node.text_range().start().into()..node.text_range().end().into()].to_owned())
-        //     .collect();
-
-        Ok(acc.collect())
-    }
-}