Implement list resugar

src/term/mod.rs

@@ -230,6 +230,14 @@ impl Tag {
   pub fn string_scons_head() -> Self {
     Self::Named(Name::new("String.SCons.head"))
   }
+
+  pub fn list() -> Self {
+    Self::Named(Name::new("List"))
+  }
+
+  pub fn list_lcons_head() -> Self {
+    Self::Named(Name::new("List.LCons.head"))
+  }
 }
 
 impl Book {

src/term/net_to_term.rs

@@ -297,6 +297,34 @@ impl<'a> Reader<'a> {
     go(term, &mut s, self);
     Term::Str { val: s }
   }
+
+  fn decode_list(&mut self, term: &mut Term) -> Term {
+    let mut els = Vec::new();
+    fn go(t: &mut Term, els: &mut Vec<Term>, rd: &mut Reader<'_>) {
+      match t {
+        Term::Lam { tag, bod, .. } if *tag == Tag::list() => go(bod, els, rd),
+        Term::App { tag, arg, .. } if *tag == Tag::list_lcons_head() => {
+          if let Term::Lam { tag, bod, .. } = &mut **arg {
+            if *tag == Tag::list() {
+              els.push(rd.decode_list(bod));
+            } else {
+              els.push(*arg.clone());
+            }
+          } else {
+            go(arg, els, rd)
+          }
+        }
+        Term::App { fun, arg, .. } => {
+          go(fun, els, rd);
+          go(arg, els, rd);
+        }
+        Term::Var { .. } => {}
+        other => els.push(other.clone()),
+      }
+    }
+    go(term, &mut els, self);
+    Term::List { els }
+  }
 }
 
 /// Represents `let (fst, snd) = val` if `tag` is `None`, and `dup#tag fst snd = val` otherwise.
@@ -492,6 +520,7 @@ impl<'a> Reader<'a> {
   fn resugar_adts(&mut self, term: &mut Term) {
     match term {
       Term::Lam { tag, bod, .. } if *tag == Tag::string() => *term = self.decode_str(bod),
+      Term::Lam { tag, bod, .. } if *tag == Tag::list() => *term = self.decode_list(bod),
       Term::Lam { tag: Tag::Named(adt_name), bod, .. } | Term::Chn { tag: Tag::Named(adt_name), bod, .. } => {
         let Some((adt_name, adt)) = self.book.adts.get_key_value(adt_name) else {
           return self.resugar_adts(bod);

tests/golden_tests/run_file/list_resugar.hvm

@@ -0,0 +1 @@
+Main = (LCons 42 (LCons (LCons @x x LNil) LNil))

tests/snapshots/run_file__list_resugar.hvm.snap

@@ -0,0 +1,5 @@
+---
+source: tests/golden_tests.rs
+input_file: tests/golden_tests/run_file/list_resugar.hvm
+---
+[42, [λd d]]

tests/snapshots/run_file__list_take.hvm.snap

@@ -2,4 +2,4 @@
 source: tests/golden_tests.rs
 input_file: tests/golden_tests/run_file/list_take.hvm
 ---
-(LCons 3 (LCons 2 LNil))
+[3, 2]