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Much better: boolean operations on newly-introduced Predicates, rather than selectors generally

This commit is contained in:
Tony Garnock-Jones 2021-08-08 16:01:29 -04:00
parent 137cc63a97
commit 61af114d5f
4 changed files with 226 additions and 238 deletions
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382
implementations/rust/preserves-path/src/lib.rs
View File

@ -10,7 +10,6 @@ use preserves::value::BinarySource;
use preserves::value::BytesBinarySource;
use preserves::value::CompoundClass;
use preserves::value::IOValue;
use preserves::value::Map;
use preserves::value::NestedValue;
use preserves::value::Reader;
use preserves::value::Value;
@ -26,7 +25,6 @@ use thiserror::Error;
#[derive(Debug)]
enum Binop {
Interleave,
Union,
Intersection,
}
@ -48,6 +46,10 @@ pub enum Path {
Step(IOValue, Rc<Path>),
}
pub trait Predicate: std::fmt::Debug {
fn test(&mut self, path: Rc<Path>, value: &IOValue) -> bool;
}
pub trait Step: std::fmt::Debug {
fn accept(&mut self, path: Rc<Path>, value: &IOValue);
fn finish(&mut self);
@ -69,6 +71,12 @@ impl Node {
Node(Rc::new(RefCell::new(s)))
}
pub fn test(&self, path: Rc<Path>, value: &IOValue) -> bool {
self.accept(path, value);
self.finish();
!self.reset().is_empty()
}
pub fn accept(&self, path: Rc<Path>, value: &IOValue) {
self.0.borrow_mut().accept(path, value)
}
@ -102,6 +110,12 @@ impl Path {
}
}
impl StepMaker for path::Selector {
fn connect(&self, step: Node) -> Result<Node, CompilationError> {
self.0.connect(step)
}
}
impl<S: StepMaker> StepMaker for Vec<S> {
fn connect(&self, mut step: Node) -> Result<Node, CompilationError> {
for s in self.iter().rev() {
@ -111,19 +125,48 @@ impl<S: StepMaker> StepMaker for Vec<S> {
}
}
impl StepMaker for path::Expr {
fn connect(&self, step: Node) -> Result<Node, CompilationError> {
#[derive(Debug)]
enum CompiledPredicate {
Selector(Node),
Not(Box<CompiledPredicate>),
Or(Vec<CompiledPredicate>),
And(Vec<CompiledPredicate>),
}
fn compile_predicate(p: &path::Predicate) -> Result<CompiledPredicate, CompilationError> {
match p {
path::Predicate::Selector(b) =>
Ok(CompiledPredicate::Selector((&**b).connect(BoolCollector::new())?)),
path::Predicate::Not { pred } =>
Ok(CompiledPredicate::Not(Box::new(compile_predicate(&**pred)?))),
path::Predicate::Or { preds } =>
Ok(CompiledPredicate::Or(preds.iter().map(compile_predicate).collect::<Result<_,_>>()?)),
path::Predicate::And { preds } =>
Ok(CompiledPredicate::And(preds.iter().map(compile_predicate).collect::<Result<_,_>>()?)),
}
}
impl Predicate for CompiledPredicate {
fn test(&mut self, path: Rc<Path>, value: &IOValue) -> bool {
match self {
path::Expr::Steps(s) =>
s.connect(step),
path::Expr::Not { expr } =>
expr.connect(Node::new(NotStep { seen_value: false, step, })),
path::Expr::Interleave { exprs } =>
ForkJoinStep::new(exprs, |e, s| e.connect(s), step),
path::Expr::Union { exprs } =>
ForkJoinStep::new(exprs, |e, s| e.connect(s), ThresholdStep::new(1, step)?),
path::Expr::Intersection { exprs } =>
ForkJoinStep::new(exprs, |e, s| e.connect(ThresholdStep::new(1, s)?), ThresholdStep::new(exprs.len(), step)?),
CompiledPredicate::Selector(n) => n.test(path, value),
CompiledPredicate::Not(p) => !p.test(path, value),
CompiledPredicate::Or(ps) => {
for p in ps.iter_mut() {
if p.test(Rc::clone(&path), value) {
return true;
}
}
return false;
},
CompiledPredicate::And(ps) => {
for p in ps.iter_mut() {
if !p.test(Rc::clone(&path), value) {
return false;
}
}
return true;
},
}
}
}
@ -133,7 +176,6 @@ impl StepMaker for path::Step {
match self {
path::Step::Axis(b) => (&**b).connect(step),
path::Step::Filter(b) => (&**b).connect(step),
path::Step::Expr(b) => (&**b).connect(step),
}
}
}
@ -146,18 +188,13 @@ struct AxisStep {
impl StepMaker for path::Axis {
fn connect(&self, step: Node) -> Result<Node, CompilationError> {
if let path::Axis::Nop = self {
Ok(step)
} else {
Ok(Node::new(AxisStep { step, axis: self.clone() }))
}
Ok(Node::new(AxisStep { step, axis: self.clone() }))
}
}
impl Step for AxisStep {
fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
match &self.axis {
path::Axis::Nop => self.step.accept(path, value),
path::Axis::Values => {
let path = path.step(value);
for c in value.value().children() {
@ -176,17 +213,26 @@ impl Step for AxisStep {
}
}
path::Axis::At { key } => match value.value() {
Value::Record(r) => step_index(path.step(value), r.fields(), &key, &mut self.step),
Value::Sequence(vs) => step_index(path.step(value), vs, &key, &mut self.step),
Value::Dictionary(d) => if let Some(v) = d.get(&key) {
self.step.accept(path.step(value), v)
},
_ => (),
Value::String(s) =>
step_index(path.step(value), 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),
Value::Sequence(vs) =>
step_index(path.step(value), 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)
},
_ =>
(),
},
path::Axis::Label => if let Some(r) = value.value().as_record(None) {
self.step.accept(path.step(value), r.label())
},
path::Axis::Keys => match value.value() {
Value::String(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::Symbol(s) => step_keys(path.step(value), s.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) => {
@ -198,6 +244,9 @@ impl Step for AxisStep {
_ => (),
},
path::Axis::Length => match value.value() {
Value::String(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::Symbol(s) => self.step.accept(path.step(value), &IOValue::new(s.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())),
@ -218,10 +267,17 @@ impl Step for AxisStep {
delegate_finish_and_reset!(self, self.step);
}
fn step_index(p: Rc<Path>, vs: &[IOValue], key: &IOValue, step: &mut Node) {
fn step_index<T, Ts: Iterator<Item = T>, F: FnOnce(T) -> IOValue>(
p: Rc<Path>,
mut vs: Ts,
key: &IOValue,
f: F,
step: &mut Node,
) {
if let Some(i) = key.value().as_usize() {
if i < vs.len() {
step.accept(p, &vs[i])
match vs.nth(i) {
None => (),
Some(v) => step.accept(p, &f(v)),
}
}
}
@ -236,10 +292,13 @@ impl StepMaker for path::Filter {
fn connect(&self, step: Node) -> Result<Node, CompilationError> {
match self {
path::Filter::Nop => Ok(step),
path::Filter::Fail => Ok(Node::new(InertStep)),
path::Filter::Eq { literal } => Ok(Node::new(EqStep { literal: literal.clone(), step })),
path::Filter::Compare { op, literal } => Ok(Node::new(CompareStep {
op: (**op).clone(),
literal: literal.clone(),
step,
})),
path::Filter::Regex { regex } => Ok(Node::new(RegexStep { regex: regex::Regex::new(regex)?, step })),
path::Filter::Test { expr } => Ok(Node::new(TestStep { expr: expr.connect(BoolCollector::new())?, step })),
path::Filter::Test { pred } => Ok(Node::new(TestStep { pred: compile_predicate(&**pred)?, step })),
path::Filter::Kind { kind } => Ok(Node::new(KindStep {
kind: match &**kind {
path::ValueKind::Boolean => ValueClass::Atomic(AtomClass::Boolean),
@ -271,39 +330,22 @@ impl Step for InertStep {
}
#[derive(Debug)]
struct NotStep {
seen_value: bool,
step: Node,
}
impl Step for NotStep {
fn accept(&mut self, _path: Rc<Path>, _value: &IOValue) {
self.seen_value = true;
}
fn finish(&mut self) {
if !self.seen_value {
self.step.accept(Path::root(), &IOValue::new(true));
self.seen_value = true; // makes finish() idempotent
}
self.step.finish()
}
fn reset(&mut self) -> Vec<IOValue> {
self.seen_value = false;
self.step.reset()
}
}
#[derive(Debug)]
struct EqStep {
struct CompareStep {
op: path::Comparison,
literal: IOValue,
step: Node,
}
impl Step for EqStep {
impl Step for CompareStep {
fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
if value == &self.literal {
if match self.op {
path::Comparison::Eq => value == &self.literal,
path::Comparison::Ne => value != &self.literal,
path::Comparison::Lt => value < &self.literal,
path::Comparison::Ge => value >= &self.literal,
path::Comparison::Gt => value > &self.literal,
path::Comparison::Le => value <= &self.literal,
} {
self.step.accept(path, value)
}
}
@ -331,17 +373,14 @@ impl Step for RegexStep {
#[derive(Debug)]
struct TestStep {
expr: Node,
pred: CompiledPredicate,
step: Node,
}
impl Step for TestStep {
fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
self.expr.accept(Rc::clone(&path), value);
self.expr.finish();
match self.expr.reset().len() {
0 => (),
_ => self.step.accept(path, value)
if self.pred.test(Rc::clone(&path), value) {
self.step.accept(path, value)
}
}
@ -414,136 +453,57 @@ impl Step for KindStep {
delegate_finish_and_reset!(self, self.step);
}
#[derive(Debug)]
struct ForkJoinStep {
branches: Vec<Node>,
step: Node,
}
impl ForkJoinStep {
fn new<F: Fn(&path::Expr, Node) -> Result<Node, CompilationError>>(
exprs: &Vec<path::Expr>,
f: F,
step: Node,
) -> Result<Node, CompilationError> {
Ok(Node::new(Self {
branches: exprs.iter().map(|e| f(e, step.clone())).collect::<Result<Vec<Node>, _>>()?,
step,
}))
}
}
impl Step for ForkJoinStep {
fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
for n in self.branches.iter_mut() {
n.accept(Rc::clone(&path), value)
}
}
fn finish(&mut self) {
for n in self.branches.iter_mut() {
n.finish()
}
self.step.finish()
}
fn reset(&mut self) -> Vec<IOValue> {
let result = self.step.reset();
for n in self.branches.iter_mut() {
n.reset();
}
result
}
}
#[derive(Debug)]
struct ThresholdStep {
threshold: usize,
accumulator: Map<IOValue, usize>,
step: Node,
}
impl ThresholdStep {
fn new(threshold: usize, step: Node) -> Result<Node, CompilationError> {
Ok(Node::new(Self {
threshold,
accumulator: Map::new(),
step,
}))
}
}
impl Step for ThresholdStep {
fn accept(&mut self, path: Rc<Path>, value: &IOValue) {
let c = self.accumulator.entry(value.clone()).or_insert(0);
*c += 1;
if *c == self.threshold {
self.step.accept(path, value)
}
}
fn finish(&mut self) {
self.step.finish()
}
fn reset(&mut self) -> Vec<IOValue> {
self.accumulator.clear();
self.step.reset()
}
}
fn split_values_by_symbol(tokens: &Vec<IOValue>, separator: &str) -> Vec<Vec<IOValue>> {
fn split_values_by_symbol<'a>(tokens: &'a [IOValue], separator: &str) -> Vec<&'a [IOValue]> {
tokens
.split(|t| matches!(t.value().as_symbol(), Some(s) if s == separator))
.map(|ts| ts.to_vec())
.collect()
}
fn split_binop(tokens: &Vec<IOValue>) -> Result<(Vec<Vec<IOValue>>, Option<Binop>), CompilationError> {
let interleave_pieces = split_values_by_symbol(&tokens, "~");
fn split_binop(tokens: &[IOValue]) -> Result<(Vec<&[IOValue]>, Option<Binop>), CompilationError> {
let union_pieces = split_values_by_symbol(&tokens, "+");
let intersection_pieces = split_values_by_symbol(&tokens, "&");
match (interleave_pieces.len(), union_pieces.len(), intersection_pieces.len()) {
(1, 1, 1) => Ok((interleave_pieces, None)),
(m, 1, 1) if m > 1 => Ok((interleave_pieces, Some(Binop::Interleave))),
(1, m, 1) if m > 1 => Ok((union_pieces, Some(Binop::Union))),
(1, 1, m) if m > 1 => Ok((intersection_pieces, Some(Binop::Intersection))),
match (union_pieces.len(), intersection_pieces.len()) {
(1, 1) => Ok((union_pieces, None)),
(_, 1) => Ok((union_pieces, Some(Binop::Union))),
(1, _) => Ok((intersection_pieces, Some(Binop::Intersection))),
_ => Err(CompilationError::MixedOperators),
}
}
pub fn parse_expr(tokens: &Vec<IOValue>) -> Result<path::Expr, CompilationError> {
let (pieces, binop) = split_binop(tokens)?;
match binop {
None => parse_non_binop(&pieces[0]),
Some(o) => {
let exprs = pieces.into_iter().map(|ts| parse_non_binop(&ts))
.collect::<Result<Vec<path::Expr>, _>>()?;
Ok(match o {
Binop::Interleave => path::Expr::Interleave { exprs },
Binop::Union => path::Expr::Union { exprs },
Binop::Intersection => path::Expr::Intersection { exprs },
})
}
}
}
fn parse_non_binop(tokens: &[IOValue]) -> Result<path::Expr, CompilationError> {
if !tokens.is_empty() {
let t = tokens[0].value();
if let Some("!") = t.as_symbol().map(|s| s.as_str()) {
return Ok(path::Expr::Not { expr: Box::new(parse_non_binop(&tokens[1..])?) });
}
}
pub fn parse_selector(tokens: &[IOValue]) -> Result<path::Selector, CompilationError> {
let mut steps = Vec::new();
let mut tokens = tokens;
while let Some((s, remaining)) = parse_step(tokens)? {
steps.push(s);
tokens = remaining;
}
Ok(path::Expr::Steps(steps))
Ok(path::Selector(steps))
}
pub fn parse_predicate(tokens: &[IOValue]) -> Result<path::Predicate, CompilationError> {
let (pieces, binop) = split_binop(tokens)?;
match binop {
None => parse_non_binop(&pieces[0]),
Some(o) => {
let preds = pieces.into_iter().map(|ts| parse_non_binop(&ts)).collect::<Result<_,_>>()?;
Ok(match o {
Binop::Union => path::Predicate::Or { preds },
Binop::Intersection => path::Predicate::And { preds },
})
}
}
}
fn parse_non_binop(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..])?) });
}
}
Ok(path::Predicate::Selector(Box::new(parse_selector(tokens)?)))
}
fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, CompilationError> {
@ -554,15 +514,14 @@ fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, Co
let remainder = &tokens[1..];
if tokens[0].value().is_sequence() {
return Ok(Some((
path::Step::Expr(Box::new(parse_expr(tokens[0].value().as_sequence().unwrap())?)),
remainder)));
return Ok(Some((path::Step::Filter(Box::new(path::Filter::Test {
pred: Box::new(parse_predicate(tokens[0].value().as_sequence().unwrap())?),
})), remainder)));
}
match tokens[0].value().as_symbol() {
None => return Err(CompilationError::InvalidStep),
Some(t) => match t.as_str() {
".=" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Nop)), remainder))),
"/" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Values)), remainder))),
"//" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Descendants)), remainder))),
"." => {
@ -575,30 +534,30 @@ fn parse_step(tokens: &[IOValue]) -> Result<Option<(path::Step, &[IOValue])>, Co
".annotations" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Annotations)), remainder))),
".embedded" => Ok(Some((path::Step::Axis(Box::new(path::Axis::Embedded)), remainder))),
"=*" => Ok(Some((path::Step::Filter(Box::new(path::Filter::Nop)), remainder))),
"=!" => Ok(Some((path::Step::Filter(Box::new(path::Filter::Fail)), remainder))),
"=" => {
let (literal, remainder) = pop_step_arg(remainder)?;
Ok(Some((path::Step::Filter(Box::new(path::Filter::Eq { literal })), remainder)))
}
"=r" => {
"*" => Ok(Some((path::Step::Filter(Box::new(path::Filter::Nop)), remainder))),
"eq" => parse_comparison(remainder, path::Comparison::Eq),
"=" => parse_comparison(remainder, path::Comparison::Eq),
"ne" => parse_comparison(remainder, path::Comparison::Ne),
"lt" => parse_comparison(remainder, path::Comparison::Lt),
"gt" => parse_comparison(remainder, path::Comparison::Gt),
"le" => parse_comparison(remainder, path::Comparison::Le),
"ge" => parse_comparison(remainder, path::Comparison::Ge),
"re" | "=r" => {
let (regex_val, remainder) = pop_step_arg(remainder)?;
let regex = regex_val.value().to_string().map_err(|_| CompilationError::InvalidStep)?.clone();
let _ = regex::Regex::new(&regex)?;
Ok(Some((path::Step::Filter(Box::new(path::Filter::Regex { regex })), remainder)))
}
"?" => {
let (expr_val, remainder) = pop_step_arg(remainder)?;
let expr = Box::new(parse_expr(&vec![expr_val])?);
Ok(Some((path::Step::Filter(Box::new(path::Filter::Test { expr })), remainder)))
}
"^" => {
let (literal, remainder) = pop_step_arg(remainder)?;
Ok(Some((path::Step::Filter(Box::new(path::Filter::Test {
expr: Box::new(path::Expr::Steps(vec![
pred: Box::new(path::Predicate::Selector(Box::new(path::Selector(vec![
path::Step::Axis(Box::new(path::Axis::Label)),
path::Step::Filter(Box::new(path::Filter::Eq { literal })),
])),
path::Step::Filter(Box::new(path::Filter::Compare {
op: Box::new(path::Comparison::Eq),
literal,
})),
])))),
})), remainder)))
}
@ -635,7 +594,18 @@ fn pop_step_arg(tokens: &[IOValue]) -> Result<(IOValue, &[IOValue]), Compilation
Ok((tokens[0].clone(), &tokens[1..]))
}
impl path::Expr {
fn parse_comparison(
tokens: &[IOValue],
op: path::Comparison,
) -> Result<Option<(path::Step, &[IOValue])>, CompilationError> {
let (literal, remainder) = pop_step_arg(tokens)?;
Ok(Some((path::Step::Filter(Box::new(path::Filter::Compare {
op: Box::new(op),
literal,
})), remainder)))
}
impl path::Selector {
pub fn compile(&self) -> Result<Node, CompilationError> {
self.connect(VecCollector::new())
}
@ -645,20 +615,20 @@ impl path::Expr {
}
}
impl std::str::FromStr for path::Expr {
impl std::str::FromStr for path::Selector {
type Err = CompilationError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
parse_expr(&(BytesBinarySource::new(s.as_bytes())
.text_iovalues()
.configured(false)
.collect::<Result<Vec<_>, _>>()?))
parse_selector(&(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::Expr::from_str(s)?;
let expr = path::Selector::from_str(s)?;
expr.compile()
}
}

8
path/path.bin
View File

@ -1,7 +1,7 @@
´³schema·³version‘³ definitions·³Axis´³orµµ±nop´³rec´³lit³nop„´³tupleµ„„„„µ±values´³rec´³lit³values„´³tupleµ„„„„µ± descendants´³rec´³lit³ descendants„´³tupleµ„„„„µ±at´³rec´³lit³at„´³tupleµ´³named³key³any„„„„„µ±label´³rec´³lit³label„´³tupleµ„„„„µ±keys´³rec´³lit³keys„´³tupleµ„„„„µ±length´³rec´³lit³length„´³tupleµ„„„„µ± annotations´³rec´³lit³ annotations„´³tupleµ„„„„µ±embedded´³rec´³lit³embedded„´³tupleµ„„„„„„³Expr´³orµµ±steps´³seqof´³refµ„³Step„„„µ±not´³rec´³lit³not„´³tupleµ´³named³expr´³refµ„³Expr„„„„„„µ±
interleave´³rec´³lit³
interleave„´³tupleµ´³named³exprs´³seqof´³refµ„³Expr„„„„„„„µ±union´³rec´³lit³union„´³tupleµ´³named³exprs´³seqof´³refµ„³Expr„„„„„„„µ± intersection´³rec´³lit³ intersection„´³tupleµ´³named³exprs´³seqof´³refµ„³Expr„„„„„„„„„³Step´³orµµ±Axis´³refµ„³Axis„„µ±Filter´³refµ„³Filter„„µ±Expr´³refµ„³Expr„„„„³Filter´³orµµ±nop´³rec´³lit³nop„´³tupleµ„„„„µ±fail´³rec´³lit³fail„´³tupleµ„„„„µ±eq´³rec´³lit³eq„´³tupleµ´³named³literal³any„„„„„µ±regex´³rec´³lit³regex„´³tupleµ´³named³regex´³atom³String„„„„„„µ±test´³rec´³lit³test„´³tupleµ´³named³expr´³refµ„³Expr„„„„„„µ±kind´³rec´³lit³kind„´³tupleµ´³named³kind´³refµ„³ ValueKind„„„„„„„„³ ValueKind´³orµµ±Boolean´³lit³Boolean„„µ±Float´³lit³Float„„µ±Double´³lit³Double„„µ± SignedInteger´³lit³ SignedInteger„„µ±String´³lit³String„„µ±
´³schema·³version‘³ definitions·³Axis´³orµµ±values´³rec´³lit³values„´³tupleµ„„„„µ± descendants´³rec´³lit³ descendants„´³tupleµ„„„„µ±at´³rec´³lit³at„´³tupleµ´³named³key³any„„„„„µ±label´³rec´³lit³label„´³tupleµ„„„„µ±keys´³rec´³lit³keys„´³tupleµ„„„„µ±length´³rec´³lit³length„´³tupleµ„„„„µ± annotations´³rec´³lit³ annotations„´³tupleµ„„„„µ±embedded´³rec´³lit³embedded„´³tupleµ„„„„„„³Step´³orµµ±Axis´³refµ„³Axis„„µ±Filter´³refµ„³Filter„„„„³Filter´³orµµ±nop´³rec´³lit³nop„´³tupleµ„„„„µ±compare´³rec´³lit³compare„´³tupleµ´³named³op´³refµ„³
Comparison„„´³named³literal³any„„„„„µ±regex´³rec´³lit³regex„´³tupleµ´³named³regex´³atom³String„„„„„„µ±test´³rec´³lit³test„´³tupleµ´³named³pred´³refµ„³ Predicate„„„„„„µ±kind´³rec´³lit³kind„´³tupleµ´³named³kind´³refµ„³ ValueKind„„„„„„„„³Selector´³seqof´³refµ„³Step„„³ Predicate´³orµµ±Selector´³refµ„³Selector„„µ±not´³rec´³lit³not„´³tupleµ´³named³pred´³refµ„³ Predicate„„„„„„µ±or´³rec´³lit³or„´³tupleµ´³named³preds´³seqof´³refµ„³ Predicate„„„„„„„µ±and´³rec´³lit³and„´³tupleµ´³named³preds´³seqof´³refµ„³ Predicate„„„„„„„„„³ ValueKind´³orµµ±Boolean´³lit³Boolean„„µ±Float´³lit³Float„„µ±Double´³lit³Double„„µ± SignedInteger´³lit³ SignedInteger„„µ±String´³lit³String„„µ±
ByteString´³lit³
ByteString„„µ±Symbol´³lit³Symbol„„µ±Record´³lit³Record„„µ±Sequence´³lit³Sequence„„µ±Set´³lit³Set„„µ±
Dictionary´³lit³
Dictionary„„µ±Embedded´³lit³Embedded„„„„„³ embeddedType€„„
Dictionary„„µ±Embedded´³lit³Embedded„„„„³
Comparison´³orµµ±eq´³lit³eq„„µ±ne´³lit³ne„„µ±lt´³lit³lt„„µ±ge´³lit³ge„„µ±gt´³lit³gt„„µ±le´³lit³le„„„„„³ embeddedType€„„

23
path/path.prs
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@ -1,17 +1,17 @@
version 1 .
Expr =
/ @steps [Step ...]
/ <not @expr Expr>
/ <interleave @exprs [Expr ...]>
/ <union @exprs [Expr ...]>
/ <intersection @exprs [Expr ...]>
Selector = [Step ...] .
Predicate =
/ Selector
/ <not @pred Predicate>
/ <or @preds [Predicate ...]>
/ <and @preds [Predicate ...]>
.
Step = Axis / Filter / Expr .
Step = Axis / Filter .
Axis =
/ <nop>
/ <values>
/ <descendants>
/ <at @key any>
@ -24,13 +24,14 @@ Axis =
Filter =
/ <nop>
/ <fail>
/ <eq @literal any>
/ <compare @op Comparison @literal any>
/ <regex @regex string>
/ <test @expr Expr>
/ <test @pred Predicate>
/ <kind @kind ValueKind>
.
Comparison = =eq / =ne / =lt / =ge / =gt / =le .
ValueKind =
/ =Boolean / =Float / =Double / =SignedInteger / =String / =ByteString / =Symbol
/ =Record / =Sequence / =Set / =Dictionary

51
preserves-path.md
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@ -15,29 +15,35 @@ general-value for dictionaries); into all keys; into all
mapped-to-values, i.e. children (n.b. not just for sequences and
dicts, but also for sets).
## Expressions
## Selector
Expressions: compute a sequence or set (or dictionary?) of results
from a stream of input values.
A sequence of steps, applied one after the other, flatmap-style.
step ... ;; Applies steps one after the other, flatmap-style
Each step transforms an input document into zero or more related
documents. A step is an axis or a filter.
## Predicates
Predicates: interpret selectors as truth-functions over inputs
(nonempty output meaning truth), and compose them using and, not, or,
etc.
Precedence groupings from highest to lowest. Within a grouping, no
mixed precedence is permitted.
step ... ;; Applies steps one after the other, flatmap-style
selector ;; Applies steps one after the other, flatmap-style
! expr ;; If no nodes, yields a dummy #t node; if some, yields none
! pred ;; "not" of a predicate
expr ~ expr ~ ... ;; "interleave" of expressions (sequence-valued, duplicates allowed)
expr + expr + ... ;; "union" of expressions (set-valued)
expr & expr & ... ;; "intersection" of expressions (set-valued)
A step is an axis, a filter, or `[expr]`, a parenthesis for overriding precedence.
pred + pred + ... ;; "or" of predicates
pred & pred & ... ;; "and" of predicates
## Axes
Axes: move around, applying filters after moving
.= ;; Doesn't move anywhere
/ ;; Moves into immediate children (values / fields)
// ;; Flattens children recursively
. key ;; Moves into named child
@ -47,19 +53,30 @@ Axes: move around, applying filters after moving
.annotations ;; Moves into any annotations that might be present
.embedded ;; Moves into the representation of an embedded value
Sets have children, but no keys/length; Strings, ByteStrings and
Symbols have no children, but have keys/length.
## Filters
Filters: narrow down a selection without moving
=* ;; Accepts all
=! ;; Rejects all
* ;; Accepts all
[!] ;; Rejects all (just a use of `[pred]`)
= literal ;; Matches values equal to the literal
=r regex ;; Matches strings and symbols by regular expression
eq literal ;; Matches values (equal to/less than/greater than/etc.) the literal
= literal
ne literal
lt literal
gt literal
le literal
ge literal
?[expr] ;; Applies the expression to each node; keeps nodes that yield nonempty
re regex ;; Matches strings and symbols by regular expression
=r regex
^ literal ;; Matches a record having a the literal as its label -- equivalent to ?[.^ = literal]
[pred] ;; Applies predicate to each input; keeps inputs yielding truth
^ literal ;; Matches a record having a the literal as its label -- equivalent to [.^ = literal]
bool ;; Type filters
float