From ed63d46348c0de8a557c664f72655eeccca59723 Mon Sep 17 00:00:00 2001
From: Tony Garnock-Jones <tonyg@leastfixedpoint.com>
Date: Tue, 16 Nov 2021 22:10:04 +0100
Subject: [PATCH] Experimental schema interpreter and preserves-path support

---
 .../rust/preserves-path/Cargo.toml            |   6 +-
 implementations/rust/preserves-path/path.bin  |   2 +-
 .../rust/preserves-path/src/context.rs        |  48 ++++
 .../rust/preserves-path/src/error.rs          |   2 +
 .../rust/preserves-path/src/lib.rs            |   5 +-
 .../rust/preserves-path/src/parse.rs          |  62 +++--
 .../rust/preserves-path/src/path.rs           |  18 --
 .../rust/preserves-path/src/predicate.rs      |  20 +-
 .../rust/preserves-path/src/step.rs           | 161 ++++++------
 .../rust/preserves-schema/Cargo.toml          |   2 +-
 .../rust/preserves-schema/src/compiler/mod.rs |  54 ++--
 .../preserves-schema/src/support/interpret.rs | 233 ++++++++++++++++++
 .../rust/preserves-schema/src/support/mod.rs  |   2 +
 .../rust/preserves-tools/Cargo.toml           |   5 +-
 .../preserves-tools/src/bin/preserves-tool.rs |  46 ++--
 path/path.bin                                 |   2 +-
 path/path.prs                                 |   2 +
 preserves-path.md                             |   2 +
 18 files changed, 493 insertions(+), 179 deletions(-)
 create mode 100644 implementations/rust/preserves-path/src/context.rs
 delete mode 100644 implementations/rust/preserves-path/src/path.rs
 create mode 100644 implementations/rust/preserves-schema/src/support/interpret.rs

diff --git a/implementations/rust/preserves-path/Cargo.toml b/implementations/rust/preserves-path/Cargo.toml
index ab2ff90..1154c48 100644
--- a/implementations/rust/preserves-path/Cargo.toml
+++ b/implementations/rust/preserves-path/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "preserves-path"
-version = "2.2.0"
+version = "3.0.0"
 authors = ["Tony Garnock-Jones <tonyg@leastfixedpoint.com>"]
 edition = "2018"
 description = "Implementation of preserves-path, a query language for Preserves documents."
@@ -9,11 +9,11 @@ repository = "https://gitlab.com/preserves/preserves"
 license = "Apache-2.0"
 
 [build-dependencies]
-preserves-schema = { path = "../preserves-schema", version = "^2.2.0"}
+preserves-schema = { path = "../preserves-schema", version = "^2.3.0"}
 
 [dependencies]
 preserves = { path = "../preserves", version = "^2.2.0"}
-preserves-schema = { path = "../preserves-schema", version = "^2.2.0"}
+preserves-schema = { path = "../preserves-schema", version = "^2.3.0"}
 
 num = "0.4"
 regex = "1.5"
diff --git a/implementations/rust/preserves-path/path.bin b/implementations/rust/preserves-path/path.bin
index 5f9b5e5..ca12e84 100644
--- a/implementations/rust/preserves-path/path.bin
+++ b/implementations/rust/preserves-path/path.bin
@@ -1,4 +1,4 @@
-´łschema·łversion‘łdefinitions·łAxis´łorµµ±values´łrec´łlitłvalues„´łtupleµ„„„„µ±descendants´łrec´łlitłdescendants„´łtupleµ„„„„µ±at´łrec´łlitłat„´łtupleµ´łnamedłkeyłany„„„„„µ±label´łrec´łlitłlabel„´łtupleµ„„„„µ±keys´łrec´łlitłkeys„´łtupleµ„„„„µ±length´łrec´łlitłlength„´łtupleµ„„„„µ±annotations´łrec´łlitłannotations„´łtupleµ„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„„„łStep´łorµµ±Axis´łrefµ„łAxis„„µ±Filter´łrefµ„łFilter„„„„łFilter´łorµµ±nop´łrec´łlitłnop„´łtupleµ„„„„µ±compare´łrec´łlitłcompare„´łtupleµ´łnamedłop´łrefµ„ł
+´łschema·łversion‘łdefinitions·łAxis´łorµµ±values´łrec´łlitłvalues„´łtupleµ„„„„µ±descendants´łrec´łlitłdescendants„´łtupleµ„„„„µ±at´łrec´łlitłat„´łtupleµ´łnamedłkeyłany„„„„„µ±label´łrec´łlitłlabel„´łtupleµ„„„„µ±keys´łrec´łlitłkeys„´łtupleµ„„„„µ±length´łrec´łlitłlength„´łtupleµ„„„„µ±annotations´łrec´łlitłannotations„´łtupleµ„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„µ±parse´łrec´łlitłparse„´łtupleµ´łnamedłmodule´łseqof´łatomłSymbol„„„´łnamedłname´łatomłSymbol„„„„„„µ±unparse´łrec´łlitłunparse„´łtupleµ´łnamedłmodule´łseqof´łatomłSymbol„„„´łnamedłname´łatomłSymbol„„„„„„„„łStep´łorµµ±Axis´łrefµ„łAxis„„µ±Filter´łrefµ„łFilter„„„„łFilter´łorµµ±nop´łrec´łlitłnop„´łtupleµ„„„„µ±compare´łrec´łlitłcompare„´łtupleµ´łnamedłop´łrefµ„ł
 Comparison„„´łnamedłliteralłany„„„„„µ±regex´łrec´łlitłregex„´łtupleµ´łnamedłregex´łatomłString„„„„„„µ±test´łrec´łlitłtest„´łtupleµ´łnamedłpred´łrefµ„ł	Predicate„„„„„„µ±real´łrec´łlitłreal„´łtupleµ„„„„µ±int´łrec´łlitłint„´łtupleµ„„„„µ±kind´łrec´łlitłkind„´łtupleµ´łnamedłkind´łrefµ„ł	ValueKind„„„„„„„„łSelector´łseqof´łrefµ„łStep„„ł	Predicate´łorµµ±Selector´łrefµ„łSelector„„µ±not´łrec´łlitłnot„´łtupleµ´łnamedłpred´łrefµ„ł	Predicate„„„„„„µ±or´łrec´łlitłor„´łtupleµ´łnamedłpreds´łseqof´łrefµ„ł	Predicate„„„„„„„µ±and´łrec´łlitłand„´łtupleµ´łnamedłpreds´łseqof´łrefµ„ł	Predicate„„„„„„„„„ł	ValueKind´łorµµ±Boolean´łlitłBoolean„„µ±Float´łlitłFloat„„µ±Double´łlitłDouble„„µ±
SignedInteger´łlitł
SignedInteger„„µ±String´łlitłString„„µ±
 ByteString´łlitł
 ByteString„„µ±Symbol´łlitłSymbol„„µ±Record´łlitłRecord„„µ±Sequence´łlitłSequence„„µ±Set´łlitłSet„„µ±
diff --git a/implementations/rust/preserves-path/src/context.rs b/implementations/rust/preserves-path/src/context.rs
new file mode 100644
index 0000000..b0c12fc
--- /dev/null
+++ b/implementations/rust/preserves-path/src/context.rs
@@ -0,0 +1,48 @@
+use preserves::value::IOValue;
+
+use preserves_schema::compiler::load_schema_or_bundle;
+use preserves_schema::gen::schema::Definition;
+
+use std::io;
+
+#[derive(Default)]
+pub struct Env(pub preserves_schema::support::interpret::Env<IOValue>);
+
+pub struct Context<'a> {
+    pub env: &'a Env,
+    path: Vec<IOValue>,
+}
+
+impl<'a> Context<'a> {
+    pub fn new(env: &'a Env) -> Self {
+        Context {
+            env,
+            path: Vec::new(),
+        }
+    }
+
+    pub fn with_path_step<R, F: FnOnce(&mut Self) -> R>(&mut self, v: &IOValue, f: F) -> R {
+        self.path.push(v.clone());
+        let result = f(self);
+        self.path.pop();
+        result
+    }
+}
+
+impl Env {
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    pub fn load_bundle(&mut self, filename: &std::path::PathBuf) -> io::Result<()> {
+        load_schema_or_bundle(&mut self.0, filename)
+    }
+
+    pub fn lookup_definition(&self, module: &Vec<String>, name: &str) -> Option<&Definition<IOValue>> {
+        self.0.get(module).and_then(|s| s.definitions.0.get(name))
+    }
+
+    pub fn to_context(&self) -> Context {
+        Context::new(self)
+    }
+}
diff --git a/implementations/rust/preserves-path/src/error.rs b/implementations/rust/preserves-path/src/error.rs
index 1780594..7e0afc5 100644
--- a/implementations/rust/preserves-path/src/error.rs
+++ b/implementations/rust/preserves-path/src/error.rs
@@ -10,6 +10,8 @@ pub enum CompilationError {
     MixedOperators,
     #[error("Invalid step")]
     InvalidStep,
+    #[error("Undefined schema definition name: {0}")]
+    UndefinedSchemaDefinitionName(String),
     #[error(transparent)]
     RegexError(#[from] regex::Error),
 }
diff --git a/implementations/rust/preserves-path/src/lib.rs b/implementations/rust/preserves-path/src/lib.rs
index 00a4a73..4e7b88e 100644
--- a/implementations/rust/preserves-path/src/lib.rs
+++ b/implementations/rust/preserves-path/src/lib.rs
@@ -1,6 +1,6 @@
+pub mod context;
 pub mod error;
 pub mod parse;
-pub mod path;
 pub mod predicate;
 
 pub mod schemas {
@@ -9,6 +9,9 @@ pub mod schemas {
 
 pub mod step;
 
+pub use context::Context;
+pub use context::Env;
+
 pub use error::CompilationError;
 
 pub use parse::parse_selector;
diff --git a/implementations/rust/preserves-path/src/parse.rs b/implementations/rust/preserves-path/src/parse.rs
index 6466006..05d32f5 100644
--- a/implementations/rust/preserves-path/src/parse.rs
+++ b/implementations/rust/preserves-path/src/parse.rs
@@ -1,4 +1,5 @@
 use crate::CompilationError;
+use crate::context::Env;
 use crate::schemas::path;
 use crate::step::Node;
 
@@ -33,22 +34,22 @@ fn split_binop(tokens: &[IOValue]) -> Result<(Vec<&[IOValue]>, Option<Binop>), C
     }
 }
 
-pub fn parse_selector(tokens: &[IOValue]) -> Result<path::Selector, CompilationError> {
+pub fn parse_selector(env: &Env, tokens: &[IOValue]) -> Result<path::Selector, CompilationError> {
     let mut steps = Vec::new();
     let mut tokens = tokens;
-    while let Some((s, remaining)) = parse_step(tokens)? {
+    while let Some((s, remaining)) = parse_step(env, tokens)? {
         steps.push(s);
         tokens = remaining;
     }
     Ok(path::Selector(steps))
 }
 
-pub fn parse_predicate(tokens: &[IOValue]) -> Result<path::Predicate, CompilationError> {
+pub fn parse_predicate(env: &Env, tokens: &[IOValue]) -> Result<path::Predicate, CompilationError> {
     let (pieces, binop) = split_binop(tokens)?;
     match binop {
-        None => parse_non_binop(&pieces[0]),
+        None => parse_non_binop(env, &pieces[0]),
         Some(o) => {
-            let preds = pieces.into_iter().map(|ts| parse_non_binop(&ts)).collect::<Result<_,_>>()?;
+            let preds = pieces.into_iter().map(|ts| parse_non_binop(env, &ts)).collect::<Result<_,_>>()?;
             Ok(match o {
                 Binop::Union => path::Predicate::Or { preds },
                 Binop::Intersection => path::Predicate::And { preds },
@@ -57,19 +58,29 @@ pub fn parse_predicate(tokens: &[IOValue]) -> Result<path::Predicate, Compilatio
     }
 }
 
-fn parse_non_binop(tokens: &[IOValue]) -> Result<path::Predicate, CompilationError> {
+fn parse_non_binop(env: &Env, tokens: &[IOValue]) -> Result<path::Predicate, CompilationError> {
     if !tokens.is_empty() {
         let t = tokens[0].value();
 
         if let Some("!") = t.as_symbol().map(|s| s.as_str()) {
-            return Ok(path::Predicate::Not { pred: Box::new(parse_non_binop(&tokens[1..])?) });
+            return Ok(path::Predicate::Not { pred: Box::new(parse_non_binop(env, &tokens[1..])?) });
         }
     }
 
-    Ok(path::Predicate::Selector(Box::new(parse_selector(tokens)?)))
+    Ok(path::Predicate::Selector(Box::new(parse_selector(env, tokens)?)))
 }
 
-fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, CompilationError> {
+fn parse_schema_definition_name(env: &Env, token: &IOValue) -> Result<(Vec<String>, String), CompilationError> {
+    let defpath = token.value().to_symbol().map_err(|_| CompilationError::InvalidStep)?;
+    let mut module: Vec<String> = defpath.split('.').map(|s| s.to_string()).collect();
+    let name = module.pop().expect("at least one element in the Schema name");
+    match env.lookup_definition(&module, &name) {
+        Some(_) => Ok((module, name)),
+        None => Err(CompilationError::UndefinedSchemaDefinitionName(format!("{:?}", token))),
+    }
+}
+
+fn parse_step<'a>(env: &Env, tokens: &'a [IOValue]) -> Result<Option<(path::Step, &'a [IOValue])>, CompilationError> {
     if tokens.is_empty() {
         return Ok(None);
     }
@@ -78,7 +89,7 @@ fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, Co
 
     if tokens[0].value().is_sequence() {
         return Ok(Some((path::Step::Filter(Box::new(path::Filter::Test {
-            pred: Box::new(parse_predicate(tokens[0].value().as_sequence().unwrap())?),
+            pred: Box::new(parse_predicate(env, tokens[0].value().as_sequence().unwrap())?),
         })), remainder)));
     }
 
@@ -96,7 +107,16 @@ fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, Co
             ".length" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Length)), remainder))),
             ".annotations" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Annotations)), remainder))),
             ".embedded" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Embedded)), remainder))),
-
+            "%" => {
+                let (defpath, remainder) = pop_step_arg(remainder)?;
+                let (module, name) = parse_schema_definition_name(env, &defpath)?;
+                Ok(Some((path::Step::Axis(Box::new(path::Axis::Parse { module, name })), remainder)))
+            }
+            "%-" => {
+                let (defpath, remainder) = pop_step_arg(remainder)?;
+                let (module, name) = parse_schema_definition_name(env, &defpath)?;
+                Ok(Some((path::Step::Axis(Box::new(path::Axis::Unparse { module, name })), remainder)))
+            }
             "*" => Ok(Some((path::Step::Filter(Box::new(path::Filter::Nop)), remainder))),
             "eq" | "=" => parse_comparison(remainder, path::Comparison::Eq),
             "ne" | "!=" => parse_comparison(remainder, path::Comparison::Ne),
@@ -170,20 +190,18 @@ fn parse_comparison(
     })), remainder)))
 }
 
-impl std::str::FromStr for path::Selector {
-    type Err = CompilationError;
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        parse_selector(&(BytesBinarySource::new(s.as_bytes())
-                         .text_iovalues()
-                         .configured(false)
-                         .collect::<Result<Vec<_>, _>>()?))
+impl path::Selector {
+    pub fn from_str(env: &Env, s: &str) -> Result<Self, CompilationError> {
+        parse_selector(env, &(BytesBinarySource::new(s.as_bytes())
+                              .text_iovalues()
+                              .configured(false)
+                              .collect::<Result<Vec<_>, _>>()?))
     }
 }
 
-impl std::str::FromStr for Node {
-    type Err = CompilationError;
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        let expr = path::Selector::from_str(s)?;
+impl Node {
+    pub fn from_str(env: &Env, s: &str) -> Result<Self, CompilationError> {
+        let expr = path::Selector::from_str(env, s)?;
         expr.compile()
     }
 }
diff --git a/implementations/rust/preserves-path/src/path.rs b/implementations/rust/preserves-path/src/path.rs
deleted file mode 100644
index adf6fed..0000000
--- a/implementations/rust/preserves-path/src/path.rs
+++ /dev/null
@@ -1,18 +0,0 @@
-use preserves::value::IOValue;
-
-use std::rc::Rc;
-
-pub enum Path {
-    Root,
-    Step(IOValue, Rc<Path>),
-}
-
-impl Path {
-    pub fn root() -> Rc<Self> {
-        Rc::new(Path::Root)
-    }
-
-    pub fn step(self: &Rc<Self>, v: &IOValue) -> Rc<Self> {
-        Rc::new(Path::Step(v.clone(), Rc::clone(self)))
-    }
-}
diff --git a/implementations/rust/preserves-path/src/predicate.rs b/implementations/rust/preserves-path/src/predicate.rs
index d2fd026..1c7594f 100644
--- a/implementations/rust/preserves-path/src/predicate.rs
+++ b/implementations/rust/preserves-path/src/predicate.rs
@@ -1,5 +1,5 @@
 use crate::CompilationError;
-use crate::path::Path;
+use crate::context::Context;
 use crate::schemas::path;
 use crate::step::BoolCollector;
 use crate::step::Node;
@@ -7,10 +7,8 @@ use crate::step::StepMaker;
 
 use preserves::value::IOValue;
 
-use std::rc::Rc;
-
 pub trait Predicate: std::fmt::Debug {
-    fn test(&mut self, path: Rc<Path>, value: &IOValue) -> bool;
+    fn test(&mut self, ctxt: &mut Context, value: &IOValue) -> bool;
 }
 
 #[derive(Debug)]
@@ -35,19 +33,19 @@ impl path::Predicate {
         }
     }
 
-    pub fn exec(&self, value: &IOValue) -> Result<bool, CompilationError> {
-        Ok(self.compile()?.test(Path::root(), value))
+    pub fn exec(&self, ctxt: &mut Context, value: &IOValue) -> Result<bool, CompilationError> {
+        Ok(self.compile()?.test(ctxt, value))
     }
 }
 
 impl Predicate for CompiledPredicate {
-    fn test(&mut self, path: Rc<Path>, value: &IOValue) -> bool {
+    fn test(&mut self, ctxt: &mut Context, value: &IOValue) -> bool {
         match self {
-            CompiledPredicate::Selector(n) => n.test(path, value),
-            CompiledPredicate::Not(p) => !p.test(path, value),
+            CompiledPredicate::Selector(n) => n.test(ctxt, value),
+            CompiledPredicate::Not(p) => !p.test(ctxt, value),
             CompiledPredicate::Or(ps) => {
                 for p in ps.iter_mut() {
-                    if p.test(Rc::clone(&path), value) {
+                    if p.test(ctxt, value) {
                         return true;
                     }
                 }
@@ -55,7 +53,7 @@ impl Predicate for CompiledPredicate {
             },
             CompiledPredicate::And(ps) => {
                 for p in ps.iter_mut() {
-                    if !p.test(Rc::clone(&path), value) {
+                    if !p.test(ctxt, value) {
                         return false;
                     }
                 }
diff --git a/implementations/rust/preserves-path/src/step.rs b/implementations/rust/preserves-path/src/step.rs
index ad483a9..f947148 100644
--- a/implementations/rust/preserves-path/src/step.rs
+++ b/implementations/rust/preserves-path/src/step.rs
@@ -2,7 +2,7 @@
 // If we could make Schemas produce generics...
 
 use crate::CompilationError;
-use crate::path::Path;
+use crate::context::Context;
 use crate::predicate::CompiledPredicate;
 use crate::predicate::Predicate;
 use crate::schemas::path;
@@ -18,8 +18,9 @@ use preserves::value::NestedValue;
 use preserves::value::Value;
 use preserves::value::ValueClass;
 
+use preserves_schema::support::interpret;
+
 use std::cell::RefCell;
-use std::collections::VecDeque;
 use std::iter::Iterator;
 use std::rc::Rc;
 
@@ -28,7 +29,7 @@ pub trait StepMaker {
 }
 
 pub trait Step: std::fmt::Debug {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue);
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue);
     fn finish(&mut self);
     fn reset(&mut self) -> Vec<IOValue>;
 }
@@ -99,14 +100,14 @@ impl Node {
         Node(Rc::new(RefCell::new(s)))
     }
 
-    pub fn test(&self, path: Rc<Path>, value: &IOValue) -> bool {
-        self.accept(path, value);
+    pub fn test(&self, ctxt: &mut Context, value: &IOValue) -> bool {
+        self.accept(ctxt, value);
         self.finish();
         !self.reset().is_empty()
     }
 
-    pub fn accept(&self, path: Rc<Path>, value: &IOValue) {
-        self.0.borrow_mut().accept(path, value)
+    pub fn accept(&self, ctxt: &mut Context, value: &IOValue) {
+        self.0.borrow_mut().accept(ctxt, value)
     }
 
     pub fn finish(&self) {
@@ -117,8 +118,8 @@ impl Node {
         self.0.borrow_mut().reset()
     }
 
-    pub fn exec(&self, value: &IOValue) -> Vec<IOValue> {
-        self.accept(Path::root(), value);
+    pub fn exec(&self, ctxt: &mut Context, value: &IOValue) -> Vec<IOValue> {
+        self.accept(ctxt, value);
         self.finish();
         self.reset()
     }
@@ -154,83 +155,85 @@ impl StepMaker for path::Axis {
     }
 }
 
+fn descendants(ctxt: &mut Context, step: &mut Node, v: &IOValue) {
+    step.accept(ctxt, v);
+    for c in v.value().children() {
+        ctxt.with_path_step(&c, |ctxt| descendants(ctxt, step, &c));
+    }
+}
+
 impl Step for AxisStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
-        match &self.axis {
-            path::Axis::Values => {
-                let path = path.step(value);
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
+        ctxt.with_path_step(value, |ctxt| match &self.axis {
+            path::Axis::Values =>
                 for c in value.value().children() {
-                    self.step.accept(Rc::clone(&path), &c)
-                }
-            }
-            path::Axis::Descendants => {
-                let mut q = VecDeque::new();
-                q.push_back((path, value.clone()));
-                while let Some((p, c)) = q.pop_front() {
-                    let p = p.step(&c);
-                    for cc in c.value().children() {
-                        q.push_back((Rc::clone(&p), cc.clone()));
-                    }
-                    self.step.accept(p, &c)
-                }
-            }
+                    self.step.accept(ctxt, &c)
+                },
+            path::Axis::Descendants =>
+                descendants(ctxt, &mut self.step, value),
             path::Axis::At { key } => match value.value() {
                 Value::String(s) | Value::Symbol(s) =>
-                    step_index(path.step(value), s.chars(), &key, |c| IOValue::new(String::from(c)), &mut self.step),
+                    step_index(ctxt, s.chars(), &key, |c| IOValue::new(String::from(c)), &mut self.step),
                 Value::Record(r) =>
-                    step_index(path.step(value), r.fields().iter(), &key, |v| v.clone(), &mut self.step),
+                    step_index(ctxt, r.fields().iter(), &key, |v| v.clone(), &mut self.step),
                 Value::Sequence(vs) =>
-                    step_index(path.step(value), vs.iter(), &key, |v| v.clone(), &mut self.step),
+                    step_index(ctxt, vs.iter(), &key, |v| v.clone(), &mut self.step),
                 Value::Dictionary(d) =>
                     if let Some(v) = d.get(&key) {
-                        self.step.accept(path.step(value), v)
+                        self.step.accept(ctxt, v)
                     },
                 _ =>
                     (),
             },
             path::Axis::Label => if let Some(r) = value.value().as_record(None) {
-                self.step.accept(path.step(value), r.label())
+                self.step.accept(ctxt, r.label())
             },
             path::Axis::Keys => match value.value() {
                 Value::String(s) | Value::Symbol(s) =>
-                    step_keys(path.step(value), s.len(), &mut self.step),
-                Value::ByteString(bs) => step_keys(path.step(value), bs.len(), &mut self.step),
-                Value::Record(r) => step_keys(path.step(value), r.arity(), &mut self.step),
-                Value::Sequence(vs) => step_keys(path.step(value), vs.len(), &mut self.step),
-                Value::Dictionary(d) => {
-                    let path = path.step(value);
+                    step_keys(ctxt, s.len(), &mut self.step),
+                Value::ByteString(bs) => step_keys(ctxt, bs.len(), &mut self.step),
+                Value::Record(r) => step_keys(ctxt, r.arity(), &mut self.step),
+                Value::Sequence(vs) => step_keys(ctxt, vs.len(), &mut self.step),
+                Value::Dictionary(d) =>
                     for k in d.keys() {
-                        self.step.accept(Rc::clone(&path), k)
-                    }
-                },
+                        self.step.accept(ctxt, k)
+                    },
                 _ => (),
             },
             path::Axis::Length => match value.value() {
                 Value::String(s) | Value::Symbol(s) =>
-                    self.step.accept(path.step(value), &IOValue::new(s.len())),
-                Value::ByteString(bs) => self.step.accept(path.step(value), &IOValue::new(bs.len())),
-                Value::Record(r) => self.step.accept(path.step(value), &IOValue::new(r.arity())),
-                Value::Sequence(vs) => self.step.accept(path.step(value), &IOValue::new(vs.len())),
-                Value::Dictionary(d) => self.step.accept(path.step(value), &IOValue::new(d.len())),
-                _ => self.step.accept(path.step(value), &IOValue::new(0)),
+                    self.step.accept(ctxt, &IOValue::new(s.len())),
+                Value::ByteString(bs) => self.step.accept(ctxt, &IOValue::new(bs.len())),
+                Value::Record(r) => self.step.accept(ctxt, &IOValue::new(r.arity())),
+                Value::Sequence(vs) => self.step.accept(ctxt, &IOValue::new(vs.len())),
+                Value::Dictionary(d) => self.step.accept(ctxt, &IOValue::new(d.len())),
+                _ => self.step.accept(ctxt, &IOValue::new(0)),
             },
-            path::Axis::Annotations => {
-                let path = path.step(value);
+            path::Axis::Annotations =>
                 for c in value.annotations().slice() {
-                    self.step.accept(Rc::clone(&path), &c)
+                    self.step.accept(ctxt, &c)
+                },
+            path::Axis::Embedded => if let Some(d) = value.value().as_embedded() {
+                self.step.accept(ctxt, d)
+            },
+            path::Axis::Parse { module, name } => {
+                if let Some(p) = interpret::Context::new(&ctxt.env.0).dynamic_parse(module, name, value) {
+                    self.step.accept(ctxt, &p)
                 }
             }
-            path::Axis::Embedded => if let Some(d) = value.value().as_embedded() {
-                self.step.accept(path.step(value), d)
-            },
-        }
+            path::Axis::Unparse { module, name } => {
+                if let Some(p) = interpret::Context::new(&ctxt.env.0).dynamic_unparse(module, name, value) {
+                    self.step.accept(ctxt, &p)
+                }
+            }
+        })
     }
 
     delegate_finish_and_reset!(self, self.step);
 }
 
 fn step_index<T, Ts: Iterator<Item = T>, F: FnOnce(T) -> IOValue>(
-    p: Rc<Path>,
+    ctxt: &mut Context,
     mut vs: Ts,
     key: &IOValue,
     f: F,
@@ -239,14 +242,14 @@ fn step_index<T, Ts: Iterator<Item = T>, F: FnOnce(T) -> IOValue>(
     if let Some(i) = key.value().as_usize() {
         match vs.nth(i) {
             None => (),
-            Some(v) => step.accept(p, &f(v)),
+            Some(v) => step.accept(ctxt, &f(v)),
         }
     }
 }
 
-fn step_keys(p: Rc<Path>, count: usize, step: &mut Node) {
+fn step_keys(ctxt: &mut Context, count: usize, step: &mut Node) {
     for i in 0 .. count {
-        step.accept(Rc::clone(&p), &IOValue::new(i))
+        step.accept(ctxt, &IOValue::new(i))
     }
 }
 
@@ -285,7 +288,7 @@ impl StepMaker for path::Filter {
 }
 
 impl Step for CompareStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
         if match self.op {
             path::Comparison::Eq => value == &self.literal,
             path::Comparison::Ne => value != &self.literal,
@@ -294,7 +297,7 @@ impl Step for CompareStep {
             path::Comparison::Gt => value > &self.literal,
             path::Comparison::Le => value <= &self.literal,
         } {
-            self.step.accept(path, value)
+            self.step.accept(ctxt, value)
         }
     }
 
@@ -302,10 +305,10 @@ impl Step for CompareStep {
 }
 
 impl Step for RegexStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
         match value.value() {
             Value::String(s) | Value::Symbol(s) =>
-                if self.regex.is_match(s) { self.step.accept(path, value) },
+                if self.regex.is_match(s) { self.step.accept(ctxt, value) },
             _ =>
                 (),
         }
@@ -315,9 +318,9 @@ impl Step for RegexStep {
 }
 
 impl Step for TestStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
-        if self.pred.test(Rc::clone(&path), value) {
-            self.step.accept(path, value)
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
+        if self.pred.test(ctxt, value) {
+            self.step.accept(ctxt, value)
         }
     }
 
@@ -325,13 +328,13 @@ impl Step for TestStep {
 }
 
 impl Step for RealStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
         match value.value() {
             Value::SignedInteger(i) => if let Some(r) = BigInt::from(i).to_f64() {
-                self.step.accept(path, &IOValue::new(r))
+                self.step.accept(ctxt, &IOValue::new(r))
             },
-            Value::Float(f) => self.step.accept(path, &IOValue::new(f32::from(*f) as f64)),
-            Value::Double(_) => self.step.accept(path, value),
+            Value::Float(f) => self.step.accept(ctxt, &IOValue::new(f32::from(*f) as f64)),
+            Value::Double(_) => self.step.accept(ctxt, value),
             _ => (),
         }
     }
@@ -340,14 +343,14 @@ impl Step for RealStep {
 }
 
 impl Step for IntStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
         match value.value() {
-            Value::SignedInteger(_) => self.step.accept(path, value),
+            Value::SignedInteger(_) => self.step.accept(ctxt, value),
             Value::Float(f) => if let Some(i) = BigInt::from_f32(f32::from(*f)) {
-                self.step.accept(path, &IOValue::new(i))
+                self.step.accept(ctxt, &IOValue::new(i))
             },
             Value::Double(d) => if let Some(i) = BigInt::from_f64(f64::from(*d)) {
-                self.step.accept(path, &IOValue::new(i))
+                self.step.accept(ctxt, &IOValue::new(i))
             },
             _ => (),
         }
@@ -363,7 +366,7 @@ impl VecCollector {
 }
 
 impl Step for VecCollector {
-    fn accept(&mut self, _path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, _ctxt: &mut Context, value: &IOValue) {
         self.accumulator.push(value.clone())
     }
 
@@ -382,7 +385,7 @@ impl BoolCollector {
 }
 
 impl Step for BoolCollector {
-    fn accept(&mut self, _path: Rc<Path>, _value: &IOValue) {
+    fn accept(&mut self, _ctxt: &mut Context, _value: &IOValue) {
         self.seen_value = true
     }
 
@@ -397,9 +400,9 @@ impl Step for BoolCollector {
 }
 
 impl Step for KindStep {
-    fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
+    fn accept(&mut self, ctxt: &mut Context, value: &IOValue) {
         if value.value_class() == self.kind {
-            self.step.accept(path, value)
+            self.step.accept(ctxt, value)
         }
     }
 
@@ -411,7 +414,7 @@ impl path::Selector {
         self.connect(VecCollector::new())
     }
 
-    pub fn exec(&self, value: &IOValue) -> Result<Vec<IOValue>, CompilationError> {
-        Ok(self.compile()?.exec(value))
+    pub fn exec(&self, ctxt: &mut Context, value: &IOValue) -> Result<Vec<IOValue>, CompilationError> {
+        Ok(self.compile()?.exec(ctxt, value))
     }
 }
diff --git a/implementations/rust/preserves-schema/Cargo.toml b/implementations/rust/preserves-schema/Cargo.toml
index 923b68f..c9458f4 100644
--- a/implementations/rust/preserves-schema/Cargo.toml
+++ b/implementations/rust/preserves-schema/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "preserves-schema"
-version = "2.2.0"
+version = "2.3.0"
 authors = ["Tony Garnock-Jones <tonyg@leastfixedpoint.com>"]
 edition = "2018"
 description = "Implementation of Preserves Schema code generation and support for Rust."
diff --git a/implementations/rust/preserves-schema/src/compiler/mod.rs b/implementations/rust/preserves-schema/src/compiler/mod.rs
index ebb8c64..1fda19e 100644
--- a/implementations/rust/preserves-schema/src/compiler/mod.rs
+++ b/implementations/rust/preserves-schema/src/compiler/mod.rs
@@ -105,6 +105,33 @@ pub struct CompilerConfig {
     pub plugins: Vec<Box<dyn Plugin>>,
 }
 
+pub fn load_schema_or_bundle(bundle: &mut Map<ModulePath, Schema>, i: &PathBuf) -> io::Result<()> {
+    let mut f = File::open(&i)?;
+    let mut src = IOBinarySource::new(&mut f);
+    let mut reader = src.packed_iovalues();
+    let blob = reader.demand_next(false)?;
+    let language = Language::default();
+
+    if let Ok(s) = language.parse(&blob) {
+        let prefix = i.file_stem().ok_or_else(
+            || io::Error::new(io::ErrorKind::InvalidData,
+                              format!("Bad schema file stem: {:?}", i)))?
+            .to_str().ok_or_else(
+                || io::Error::new(io::ErrorKind::InvalidData,
+                                  format!("Invalid UTF-8 in schema file name: {:?}", i)))?;
+        bundle.insert(vec![prefix.to_owned()], s);
+    } else if let Ok(Bundle { modules }) = language.parse(&blob) {
+        for (ModulePath(k), v) in modules.0 {
+            bundle.insert(k, v);
+        }
+    } else {
+        return Err(io::Error::new(io::ErrorKind::InvalidData,
+                                  format!("Invalid schema binary blob {:?}", i)));
+    }
+
+    Ok(())
+}
+
 impl CompilerConfig {
     pub fn new(
         output_dir: PathBuf,
@@ -134,32 +161,7 @@ impl CompilerConfig {
 
     pub fn load_schemas_and_bundles(&mut self, inputs: &Vec<PathBuf>) -> io::Result<()> {
         for i in inputs {
-            let mut f = File::open(&i)?;
-            let mut src = IOBinarySource::new(&mut f);
-            let mut reader = src.packed_iovalues();
-            let blob = reader.demand_next(false)?;
-            let language = Language::default();
-
-            if let Ok(s) = language.parse(&blob) {
-                let prefix = i.file_stem().ok_or_else(
-                    || io::Error::new(io::ErrorKind::InvalidData,
-                                      format!("Bad schema file stem: {:?}", i)))?
-                    .to_str().ok_or_else(
-                        || io::Error::new(io::ErrorKind::InvalidData,
-                                          format!("Invalid UTF-8 in schema file name: {:?}", i)))?;
-                self.bundle.insert(vec![prefix.to_owned()], s);
-                continue;
-            }
-
-            if let Ok(Bundle { modules }) = language.parse(&blob) {
-                for (ModulePath(k), v) in modules.0 {
-                    self.bundle.insert(k, v);
-                }
-                continue;
-            }
-
-            return Err(io::Error::new(io::ErrorKind::InvalidData,
-                                      format!("Invalid schema binary blob {:?}", i)));
+            load_schema_or_bundle(&mut self.bundle, i)?;
         }
         Ok(())
     }
diff --git a/implementations/rust/preserves-schema/src/support/interpret.rs b/implementations/rust/preserves-schema/src/support/interpret.rs
new file mode 100644
index 0000000..23781a0
--- /dev/null
+++ b/implementations/rust/preserves-schema/src/support/interpret.rs
@@ -0,0 +1,233 @@
+use crate::gen::schema::*;
+
+use preserves::value::Map;
+use preserves::value::NestedValue;
+use preserves::value::Value;
+use preserves::value::merge::merge2;
+
+pub type Env<V> = Map<Vec<String>, Schema<V>>;
+
+#[derive(Debug)]
+pub struct Context<'a, V: NestedValue> {
+    pub env: &'a Env<V>,
+    module: Vec<String>,
+}
+
+#[derive(Debug)]
+enum DynField<V: NestedValue> {
+    Simple(V),
+    Compound(Map<V, V>),
+}
+
+impl<'a, V: NestedValue> Context<'a, V> {
+    pub fn new(env: &'a Env<V>) -> Self {
+        Context {
+            env,
+            module: Vec::new(),
+        }
+    }
+
+    pub fn dynamic_parse(&mut self, module: &Vec<String>, name: &str, v: &V) -> Option<V> {
+        let old_module = (module.len() > 0).then(|| std::mem::replace(&mut self.module, module.clone()));
+        let schema = self.env.get(&self.module);
+        let definition = schema.and_then(|s| s.definitions.0.get(name));
+        let result = definition.and_then(|d| d.dynamic_parse(self, v));
+        if let Some(m) = old_module {
+            self.module = m;
+        }
+        result
+    }
+
+    pub fn dynamic_unparse(&mut self, module: &Vec<String>, name: &str, w: &V) -> Option<V> {
+        panic!("Not yet implemented");
+    }
+}
+
+impl<V: NestedValue> Definition<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<V> {
+        match self {
+            Definition::Or { pattern_0, pattern_1, pattern_n } =>
+                pattern_0.dynamic_parse(ctxt, v)
+                .or_else(|| pattern_1.dynamic_parse(ctxt, v))
+                .or_else(|| pattern_n.iter().find_map(|p| p.dynamic_parse(ctxt, v))),
+            Definition::And { pattern_0, pattern_1, pattern_n } =>
+                pattern_0.dynamic_parse(ctxt, v)
+                .and_then(|w0| pattern_1.dynamic_parse(ctxt, v)
+                          .and_then(|w1| pattern_n.iter().fold(merge(w0, w1), |w, p| {
+                              w.and_then(|w| p.dynamic_parse(ctxt, v).and_then(
+                                  |wn| merge(w, wn)))
+                          })))
+                .map(|w| DynField::Compound(w).finish()),
+            Definition::Pattern(p) => p.dynamic_parse(ctxt, v).map(|w| w.finish()),
+        }
+    }
+}
+
+impl<V: NestedValue> NamedAlternative<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<V> {
+        self.pattern.dynamic_parse(ctxt, v).map(|w| {
+            let mut r = Value::simple_record(&self.variant_label, 1);
+            match w {
+                DynField::Simple(field) => r.fields_vec_mut().push(field),
+                DynField::Compound(fields) => if fields.len() > 0 {
+                    r.fields_vec_mut().push(V::new(fields))
+                }
+            }
+            r.finish().wrap()
+        })
+    }
+}
+
+impl<V: NestedValue> NamedPattern<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<Map<V, V>> {
+        match self {
+            NamedPattern::Named(b) => {
+                let binding = &**b;
+                binding.pattern.dynamic_parse(ctxt, v).map(|w| w.to_map(Some(&binding.name)))
+            }
+            NamedPattern::Anonymous(b) => b.dynamic_parse(ctxt, v).map(|w| w.to_map(None))
+        }
+    }
+}
+
+impl<V: NestedValue> NamedSimplePattern<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<DynField<V>> {
+        match self {
+            NamedSimplePattern::Named(b) => {
+                let binding = &**b;
+                binding.pattern.dynamic_parse(ctxt, v).map(
+                    |w| DynField::Compound(w.to_map(Some(&binding.name))))
+            }
+            NamedSimplePattern::Anonymous(b) =>
+                b.dynamic_parse(ctxt, v),
+        }
+    }
+}
+
+impl<V: NestedValue> SimplePattern<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<DynField<V>> {
+        match self {
+            SimplePattern::Any => Some(DynField::Simple(v.clone())),
+            SimplePattern::Atom { atom_kind } => match &**atom_kind {
+                AtomKind::Boolean => v.value().is_boolean().then(|| DynField::Simple(v.clone())),
+                AtomKind::Float => v.value().is_float().then(|| DynField::Simple(v.clone())),
+                AtomKind::Double => v.value().is_double().then(|| DynField::Simple(v.clone())),
+                AtomKind::SignedInteger => v.value().is_signedinteger().then(|| DynField::Simple(v.clone())),
+                AtomKind::String => v.value().is_string().then(|| DynField::Simple(v.clone())),
+                AtomKind::ByteString => v.value().is_bytestring().then(|| DynField::Simple(v.clone())),
+                AtomKind::Symbol => v.value().is_symbol().then(|| DynField::Simple(v.clone())),
+            },
+            SimplePattern::Embedded { .. } => v.value().is_embedded().then(|| DynField::Simple(v.clone())),
+            SimplePattern::Lit { value } => (v == value).then(|| DynField::Compound(Map::new())),
+            SimplePattern::Seqof { pattern } =>
+                v.value().as_sequence()
+                .and_then(|vs| vs.iter().map(|v| (**pattern).dynamic_parse(ctxt, v).map(|w| w.finish()))
+                          .collect::<Option<Vec<V>>>())
+                .map(|ws| DynField::Simple(V::new(ws))),
+            SimplePattern::Setof { pattern } =>
+                v.value().as_set()
+                .and_then(|vs| vs.iter().map(|v| (**pattern).dynamic_parse(ctxt, v).map(|w| w.finish()))
+                          .collect::<Option<Vec<V>>>())
+                .map(|ws| DynField::Simple(V::new(ws))),
+            SimplePattern::Dictof { key, value } =>
+                v.value().as_dictionary()
+                .and_then(|d| {
+                    d.iter().map(|(k, v)| {
+                        (**key).dynamic_parse(ctxt, k)
+                            .and_then(|kw| (**value).dynamic_parse(ctxt, v)
+                                      .map(|vw| (kw.finish(), vw.finish())))
+                    }).collect::<Option<Map<V, V>>>()
+                })
+                .map(|d| DynField::Simple(V::new(d))),
+            SimplePattern::Ref(r) =>
+                ctxt.dynamic_parse(&r.module.0, &r.name, v).map(DynField::Simple),
+        }
+    }
+}
+
+impl<V: NestedValue> CompoundPattern<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<Map<V, V>> {
+        match self {
+            CompoundPattern::Rec { label, fields } =>
+                v.value().as_record(None).and_then(
+                    |r| (**label).dynamic_parse(ctxt, r.label()).and_then(
+                        |lw| (**fields).dynamic_parse(ctxt, &V::new(r.fields().to_vec())).and_then(
+                            |fsw| merge(lw, fsw)))),
+            CompoundPattern::Tuple { patterns } =>
+                v.value().as_sequence().and_then(
+                    |vs| if vs.len() == patterns.len() {
+                        patterns.iter().zip(vs)
+                            .fold(Some(Map::new()), |acc, (p, v)| {
+                                acc.and_then(|acc| p.dynamic_parse(ctxt, v).and_then(
+                                    |w| merge(acc, w)))
+                            })
+                    } else {
+                        None
+                    }),
+            CompoundPattern::TuplePrefix { fixed, variable } =>
+                v.value().as_sequence().and_then(
+                    |vs| if vs.len() >= fixed.len() {
+                        fixed.iter().zip(vs)
+                            .fold(Some(Map::new()), |acc, (p, v)| {
+                                acc.and_then(|acc| p.dynamic_parse(ctxt, v).and_then(
+                                    |w| merge(acc, w)))
+                            }).and_then(|fixed_ws| {
+                                let remainder = V::new(vs[fixed.len()..].to_vec());
+                                (**variable).dynamic_parse(ctxt, &remainder).and_then(
+                                    |variable_ws| merge(fixed_ws, variable_ws.unwrap_compound()))
+                            })
+                    } else {
+                        None
+                    }),
+            CompoundPattern::Dict { entries } =>
+                v.value().as_dictionary().and_then(
+                    |d| (**entries).0.iter().fold(Some(Map::new()), |acc, (k, p)| {
+                        acc.and_then(|acc| d.get(k).and_then(|v| p.dynamic_parse(ctxt, v).and_then(
+                            |w| merge(acc, w.unwrap_compound()))))
+                    })),
+        }
+    }
+}
+
+impl<V: NestedValue> Pattern<V> {
+    fn dynamic_parse(&self, ctxt: &mut Context<V>, v: &V) -> Option<DynField<V>> {
+        match self {
+            Pattern::SimplePattern(b) => (**b).dynamic_parse(ctxt, v),
+            Pattern::CompoundPattern(b) => (**b).dynamic_parse(ctxt, v).map(DynField::Compound),
+        }
+    }
+}
+
+impl<V: NestedValue> DynField<V> {
+    fn finish(self) -> V {
+        match self {
+            DynField::Simple(v) => v,
+            DynField::Compound(v) => V::new(v),
+        }
+    }
+
+    fn to_map(self, key: Option<&str>) -> Map<V, V> {
+        match self {
+            DynField::Simple(v) => {
+                let mut d = Map::new();
+                if let Some(k) = key {
+                    d.insert(V::symbol(k), v);
+                }
+                d
+            }
+            DynField::Compound(d) => d,
+        }
+    }
+
+    fn unwrap_compound(self) -> Map<V, V> {
+        match self {
+            DynField::Simple(_) => panic!("Cannot unwrap DynField::Simple to compound fields"),
+            DynField::Compound(d) => d,
+        }
+    }
+}
+
+fn merge<V: NestedValue>(a: Map<V, V>, b: Map<V, V>) -> Option<Map<V, V>> {
+    merge2(V::new(a), V::new(b))
+        .map(|d| d.value_owned().into_dictionary().expect("merge to yield Dictionary"))
+}
diff --git a/implementations/rust/preserves-schema/src/support/mod.rs b/implementations/rust/preserves-schema/src/support/mod.rs
index e656671..c1b15a7 100644
--- a/implementations/rust/preserves-schema/src/support/mod.rs
+++ b/implementations/rust/preserves-schema/src/support/mod.rs
@@ -4,6 +4,8 @@ pub use preserves;
 pub use preserves::value::Reader;
 pub use preserves::value::boundary as B;
 
+pub mod interpret;
+
 use preserves::value::ArcValue;
 use preserves::value::Domain;
 use preserves::value::IOValue;
diff --git a/implementations/rust/preserves-tools/Cargo.toml b/implementations/rust/preserves-tools/Cargo.toml
index 7b91eb8..239acca 100644
--- a/implementations/rust/preserves-tools/Cargo.toml
+++ b/implementations/rust/preserves-tools/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "preserves-tools"
-version = "2.2.1"
+version = "2.3.0"
 authors = ["Tony Garnock-Jones <tonyg@leastfixedpoint.com>"]
 edition = "2018"
 description = "Command-line utilities for working with Preserves documents."
@@ -10,7 +10,8 @@ license = "Apache-2.0"
 
 [dependencies]
 preserves = { path = "../preserves", version = "^2.2.0"}
-preserves-path = { path = "../preserves-path", version = "^2.2.0"}
+preserves-path = { path = "../preserves-path", version = "^3.0.0"}
+preserves-schema = { path = "../preserves-schema", version = "^2.3.0"}
 
 bytes = "1.0"
 clap = "=3.0.0-beta.2"
diff --git a/implementations/rust/preserves-tools/src/bin/preserves-tool.rs b/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
index ed2fc8b..b11c32f 100644
--- a/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
+++ b/implementations/rust/preserves-tools/src/bin/preserves-tool.rs
@@ -98,8 +98,8 @@ struct Convert {
     #[clap(long, arg_enum, value_name = "on/off", default_value = "on")]
     indent: Boolish,
 
-    #[clap(long, default_value="*")]
-    select: preserves_path::Node,
+    #[clap(long="select", default_value="*")]
+    select_expr: String,
 
     #[clap(long, arg_enum, default_value="sequence")]
     select_output: SelectOutput,
@@ -112,6 +112,12 @@ struct Convert {
 
     #[clap(long, arg_enum, value_name = "on/off", default_value = "on")]
     write_annotations: Boolish,
+
+    #[clap(long, value_name = "filename")]
+    bundle: Vec<std::path::PathBuf>,
+
+    #[clap(long)]
+    schema: Option<String>,
 }
 
 #[derive(ArgEnum, Clone, Debug)]
@@ -133,7 +139,6 @@ struct StringQuotation {
     escape_spaces: bool,
 }
 
-
 #[derive(Clap, Clone, Debug)]
 enum QuotationOutput {
     String(StringQuotation),
@@ -152,11 +157,11 @@ struct Quote {
 
 #[derive(Clap, Clone, Debug)]
 enum Subcommand {
-    Convert(Convert),
     Completions {
         #[clap(arg_enum, value_name = "dialect")]
         dialect: CompletionDialect,
     },
+    Convert(Convert),
     Quote(Quote),
 }
 
@@ -169,7 +174,7 @@ struct CommandLine {
 
 fn main() -> io::Result<()> {
     let args = CommandLine::parse();
-    match args.command {
+    Ok(match args.command {
         Subcommand::Completions { dialect } => {
             let mut app = CommandLine::into_app();
             match dialect {
@@ -182,8 +187,7 @@ fn main() -> io::Result<()> {
         },
         Subcommand::Convert(c) => convert(c)?,
         Subcommand::Quote(q) => quote(q)?,
-    }
-    Ok(())
+    })
 }
 
 struct RollingBuffer<R: io::Read> {
@@ -365,6 +369,14 @@ fn print_unquoted(v: &IOValue) {
 }
 
 fn convert(c: Convert) -> io::Result<()> {
+    let mut env = preserves_path::Env::new();
+    for f in c.bundle.iter() {
+        env.load_bundle(f)?;
+    }
+    let select = preserves_path::Node::from_str(&env, &c.select_expr)
+        .map_err(|e| io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("Invalid select expression: {}: {:?}", e, c.select_expr)))?;
     let mut vs = ValueStream::new(c.input_format, c.read_annotations.into(), io::stdin());
     let write_ann: bool = c.write_annotations.into();
     let mut w: Box<dyn FnMut(&IOValue) -> io::Result<()>> = match c.output_format {
@@ -385,18 +397,24 @@ fn convert(c: Convert) -> io::Result<()> {
         }
         OutputFormat::Binary => {
             let mut p = PackedWriter::new(io::stdout());
-            Box::new(move |v| if write_ann {
-                p.write(&mut IOValueDomainCodec, v)
-            } else {
-                p.write(&mut IOValueDomainCodec, &v.strip_annotations::<IOValue>())
+            Box::new(move |v| {
+                if write_ann {
+                    p.write(&mut IOValueDomainCodec, v)?;
+                } else {
+                    p.write(&mut IOValueDomainCodec, &v.strip_annotations::<IOValue>())?;
+                }
+                Ok(())
             })
         }
         OutputFormat::Unquoted =>
-            Box::new(|v| Ok(print_unquoted(v))),
+            Box::new(|v| {
+                print_unquoted(v);
+                Ok(())
+            }),
     };
     while let Some(value) = vs.next() {
         let value = value?;
-        let matches = c.select.exec(&value);
+        let matches = select.exec(&mut env.to_context(), &value);
         if c.collect {
             match c.select_output {
                 SelectOutput::Sequence => w(&IOValue::new(matches))?,
@@ -410,7 +428,7 @@ fn convert(c: Convert) -> io::Result<()> {
         }
         if let Some(limit) = c.limit {
             if vs.count >= limit {
-                return Ok(());
+                break;
             }
         }
     }
diff --git a/path/path.bin b/path/path.bin
index 5f9b5e5..ca12e84 100644
--- a/path/path.bin
+++ b/path/path.bin
@@ -1,4 +1,4 @@
-´łschema·łversion‘łdefinitions·łAxis´łorµµ±values´łrec´łlitłvalues„´łtupleµ„„„„µ±descendants´łrec´łlitłdescendants„´łtupleµ„„„„µ±at´łrec´łlitłat„´łtupleµ´łnamedłkeyłany„„„„„µ±label´łrec´łlitłlabel„´łtupleµ„„„„µ±keys´łrec´łlitłkeys„´łtupleµ„„„„µ±length´łrec´łlitłlength„´łtupleµ„„„„µ±annotations´łrec´łlitłannotations„´łtupleµ„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„„„łStep´łorµµ±Axis´łrefµ„łAxis„„µ±Filter´łrefµ„łFilter„„„„łFilter´łorµµ±nop´łrec´łlitłnop„´łtupleµ„„„„µ±compare´łrec´łlitłcompare„´łtupleµ´łnamedłop´łrefµ„ł
+´łschema·łversion‘łdefinitions·łAxis´łorµµ±values´łrec´łlitłvalues„´łtupleµ„„„„µ±descendants´łrec´łlitłdescendants„´łtupleµ„„„„µ±at´łrec´łlitłat„´łtupleµ´łnamedłkeyłany„„„„„µ±label´łrec´łlitłlabel„´łtupleµ„„„„µ±keys´łrec´łlitłkeys„´łtupleµ„„„„µ±length´łrec´łlitłlength„´łtupleµ„„„„µ±annotations´łrec´łlitłannotations„´łtupleµ„„„„µ±embedded´łrec´łlitłembedded„´łtupleµ„„„„µ±parse´łrec´łlitłparse„´łtupleµ´łnamedłmodule´łseqof´łatomłSymbol„„„´łnamedłname´łatomłSymbol„„„„„„µ±unparse´łrec´łlitłunparse„´łtupleµ´łnamedłmodule´łseqof´łatomłSymbol„„„´łnamedłname´łatomłSymbol„„„„„„„„łStep´łorµµ±Axis´łrefµ„łAxis„„µ±Filter´łrefµ„łFilter„„„„łFilter´łorµµ±nop´łrec´łlitłnop„´łtupleµ„„„„µ±compare´łrec´łlitłcompare„´łtupleµ´łnamedłop´łrefµ„ł
 Comparison„„´łnamedłliteralłany„„„„„µ±regex´łrec´łlitłregex„´łtupleµ´łnamedłregex´łatomłString„„„„„„µ±test´łrec´łlitłtest„´łtupleµ´łnamedłpred´łrefµ„ł	Predicate„„„„„„µ±real´łrec´łlitłreal„´łtupleµ„„„„µ±int´łrec´łlitłint„´łtupleµ„„„„µ±kind´łrec´łlitłkind„´łtupleµ´łnamedłkind´łrefµ„ł	ValueKind„„„„„„„„łSelector´łseqof´łrefµ„łStep„„ł	Predicate´łorµµ±Selector´łrefµ„łSelector„„µ±not´łrec´łlitłnot„´łtupleµ´łnamedłpred´łrefµ„ł	Predicate„„„„„„µ±or´łrec´łlitłor„´łtupleµ´łnamedłpreds´łseqof´łrefµ„ł	Predicate„„„„„„„µ±and´łrec´łlitłand„´łtupleµ´łnamedłpreds´łseqof´łrefµ„ł	Predicate„„„„„„„„„ł	ValueKind´łorµµ±Boolean´łlitłBoolean„„µ±Float´łlitłFloat„„µ±Double´łlitłDouble„„µ±
SignedInteger´łlitł
SignedInteger„„µ±String´łlitłString„„µ±
 ByteString´łlitł
 ByteString„„µ±Symbol´łlitłSymbol„„µ±Record´łlitłRecord„„µ±Sequence´łlitłSequence„„µ±Set´łlitłSet„„µ±
diff --git a/path/path.prs b/path/path.prs
index 828ddf2..c0c8d88 100644
--- a/path/path.prs
+++ b/path/path.prs
@@ -20,6 +20,8 @@ Axis =
 / <length>
 / <annotations>
 / <embedded>
+/ <parse @module [symbol ...] @name symbol>
+/ <unparse @module [symbol ...] @name symbol>
 .
 
 Filter =
diff --git a/preserves-path.md b/preserves-path.md
index 5db1fd4..67ec76a 100644
--- a/preserves-path.md
+++ b/preserves-path.md
@@ -52,6 +52,8 @@ Axes: move around, applying filters after moving
         .length      ;; Moves into the number of keys
         .annotations ;; Moves into any annotations that might be present
         .embedded    ;; Moves into the representation of an embedded value
+        % name       ;; Moves into successful Preserves Schema parse of definition `name`
+        %- name      ;; Moves into successful Preserves Schema unparse of definition `name`
 
 Sets have children, but no keys/length; Strings, ByteStrings and
 Symbols have no children, but have keys/length.