New update semantics for .. (recursion)

jaq-core/src/compile.rs

@@ -68,6 +68,8 @@ pub(crate) enum Tailrec {
 pub(crate) enum Term<T = TermId> {
     /// Identity (`.`)
     Id,
+    /// Recursion (`..`)
+    Recurse,
     ToString,
 
     Int(isize),
@@ -627,7 +629,7 @@ impl<'s, F> Compiler<&'s str, F> {
         use parse::Term::*;
         match t {
             Id => Term::Id,
-            Recurse => self.term(Call("!recurse", Vec::new()), &Tr::new()),
+            Recurse => Term::Recurse,
             Arr(t) => Term::Arr(self.iterm(t.map_or_else(|| Call("!empty", Vec::new()), |t| *t))),
             Neg(t) => Term::Neg(self.iterm(*t)),
             Pipe(l, None, r) => Term::Pipe(self.iterm(*l), None, self.iterm_tr(*r, tr)),

jaq-core/src/filter.rs

@@ -249,6 +249,25 @@ fn lazy_is_lazy() {
     assert_eq!(iter.next(), Some(0));
 }
 
+/// Runs `def recurse: ., (.[]? | recurse); v | recurse`.
+fn recurse_run<'a, V: ValT + 'a>(v: V) -> ValXs<'a, V> {
+    let id = core::iter::once(Ok(v.clone()));
+    Box::new(id.chain(v.values().flat_map(Result::ok).flat_map(recurse_run)))
+}
+
+/// Runs `def recurse: (.[]? | recurse), .; v | recurse |= f`.
+///
+/// This uses a `recurse` different from that of `recurse_run`; in particular,
+/// `recurse_run` yields values from root to leafs, whereas
+/// this function performs updates from leafs to root.
+/// Performing updates from root to leafs can easily lead to
+/// nontermination or other weird effects, such as
+/// trying to update values that have been deleted.
+fn recurse_update<'a, V: ValT + 'a>(v: V, f: &dyn Update<'a, V>) -> ValXs<'a, V> {
+    use crate::path::Opt::Optional;
+    box_iter::then(v.map_values(Optional, |v| recurse_update(v, f)), f)
+}
+
 /// Combination of context and input value.
 pub type Cv<'c, V> = (Ctx<'c, V>, V);
 
@@ -309,6 +328,7 @@ impl<F: FilterT<F>> FilterT<F> for Id {
         use core::iter::once;
         match &lut.terms[self.0] {
             Ast::Id => box_once(Ok(cv.1)),
+            Ast::Recurse => recurse_run(cv.1),
             Ast::ToString => box_once(match cv.1.as_str() {
                 Some(_) => Ok(cv.1),
                 None => Ok(Self::V::from(cv.1.to_string())),
@@ -485,6 +505,7 @@ impl<F: FilterT<F>> FilterT<F> for Id {
             Ast::TryCatch(..) | Ast::Label(..) => err,
 
             Ast::Id => f(cv.1),
+            Ast::Recurse => recurse_update(cv.1, &f),
             Ast::Path(l, path) => {
                 let path = path.map_ref(|i| {
                     let cv = cv.clone();

jaq-core/src/load/mod.rs

@@ -175,10 +175,7 @@ impl<'s, P: Default> Loader<&'s str, P, ReadFn<P>> {
     ///
     /// The prelude is normally initialised with filters like `map` or `true`.
     pub fn new(prelude: impl IntoIterator<Item = Def<&'s str>>) -> Self {
-        let defs = [
-            Def::new("!recurse", Vec::new(), Term::recurse("!recurse")),
-            Def::new("!empty", Vec::new(), Term::empty()),
-        ];
+        let defs = [Def::new("!empty", Vec::new(), Term::empty())];
 
         let prelude = Module {
             body: defs.into_iter().chain(prelude).collect(),

jaq-core/src/load/parse.rs

@@ -179,21 +179,6 @@ impl<S> Term<S> {
         Self::Str(None, [StrPart::Str(s)].into())
     }
 
-    /// `..`, also known as `recurse/0`, is defined as `., (.[]? | ..)`.
-    pub(crate) fn recurse(recurse: S) -> Self {
-        // `[]?`
-        let path = (path::Part::Range(None, None), path::Opt::Optional);
-        // `.[]?` (returns array/object elements or nothing instead)
-        let path = Term::Path(Term::Id.into(), Path(Vec::from([path])));
-
-        // `..`
-        let f = Term::Call(recurse, Vec::new());
-        // .[]? | ..
-        let pipe = Term::Pipe(path.into(), None, f.into());
-        // ., (.[]? | ..)
-        Term::BinOp(Term::Id.into(), BinaryOp::Comma, pipe.into())
-    }
-
     /// `{}[]` returns zero values.
     pub(crate) fn empty() -> Self {
         // `[]`

jaq-std/tests/defs.rs

@@ -172,7 +172,7 @@ yields!(limit_inf_sumr, "[limit(3; 0 + recurse(.+1))]", [0, 1, 2]);
 yields!(limit_inf_path, "[limit(2; [1] | .[repeat(0)])]", [1, 1]);
 
 #[test]
-fn recurse() {
+fn recurse_obj() {
     let x = json!({"a":0,"b":[1]});
     gives(x.clone(), "recurse", [x, json!(0), json!([1]), json!(1)]);
 
@@ -181,19 +181,21 @@ fn recurse() {
 
     let y = [json!(2), json!(4), json!(16)];
     gives(json!(2), "recurse(. * .; . < 20)", y);
+}
 
+#[test]
+fn recurse_arr() {
     let x = json!([[[0], 1], 2, [3, [4]]]);
 
     let y = json!([[[1], 2], 3, [4, [5]]]);
     give(x.clone(), "(.. | scalars) |= .+1", y);
 
     let f = ".. |= if . < [] then .+1 else . + [42] end";
-    let y = json!([[[1, 43], 2, 43], 3, [4, [5, 43], 43], 43]);
-    // jq gives: `[[[1, 42], 2, 42], 3, [4, [5, 42], 42], 42]`
+    let y = json!([[[1, 42], 2, 42], 3, [4, [5, 42], 42], 42]);
     give(x.clone(), f, y);
 
     let f = ".. |= if . < [] then .+1 else [42] + . end";
-    let y = json!([43, [43, [43, 1], 2], 3, [43, 4, [43, 5]]]);
+    let y = json!([42, [42, [42, 1], 2], 3, [42, 4, [42, 5]]]);
     // jq fails here with: "Cannot index number with number"
     give(x.clone(), f, y);
 }