NilTrees can now store a number representation for efficiency

src/extended_to_core.rs

@@ -30,7 +30,7 @@ pub fn num_to_core(n: usize) -> Expression {
     res
 }
 
-pub fn num_to_niltree(n: usize) -> NilTree {
+pub fn num_to_nils(n: usize) -> NilTree {
     if n == 0 {
         NilTree::Nil
     } else {

src/interpret.rs

@@ -7,7 +7,7 @@ use indexmap::IndexMap;
 use regex::Regex;
 
 use crate::{
-    extended_to_core::{list_to_cons, num_to_niltree, prog_to_core, switch_to_ifs},
+    extended_to_core::{list_to_cons, prog_to_core, switch_to_ifs},
     lang::{Block, Expression, Prog, ProgName, Statement},
     niltree::{cons, NilTree},
     parser::expression,
@@ -107,7 +107,7 @@ fn eval(expr: &Expression, store: &ExecState) -> NilTree {
         E::Tl(e) => eval(e, store).tl(),
         E::Nil => NilTree::Nil,
         E::Var(var) => store.get(var).clone(),
-        E::Num(n) => num_to_niltree(*n),
+        E::Num(n) => NilTree::Num(*n),
         E::Bool(b) => match b {
             true => cons(NilTree::Nil, NilTree::Nil),
             false => NilTree::Nil,

src/niltree.rs

@@ -1,9 +1,12 @@
 use std::fmt::Display;
 
+use crate::extended_to_core::num_to_nils;
+
 #[derive(Debug, PartialEq, Eq, Clone)]
 pub enum NilTree {
     Nil,
     List(Vec<NilTree>),
+    Num(usize),
 }
 
 impl NilTree {
@@ -26,6 +29,10 @@ impl NilTree {
 
                 (h, t)
             }
+            NilTree::Num(n) => match n {
+                0 => (NilTree::Nil, NilTree::Nil),
+                n => (NilTree::Nil, NilTree::Num(n - 1)),
+            },
         }
     }
 }
@@ -37,6 +44,7 @@ pub fn cons(a: NilTree, b: NilTree) -> NilTree {
             v.push(a);
             NilTree::List(v)
         }
+        NilTree::Num(n) => cons(a, num_to_nils(n)),
     }
 }
 
@@ -60,6 +68,7 @@ impl Display for NilTree {
 
                 s.fmt(f)
             }
+            NilTree::Num(n) => num_to_nils(*n).fmt(f),
         }
     }
 }

src/output.rs

@@ -116,6 +116,7 @@ pub fn parse_num(tree: &NilTree) -> anyhow::Result<usize> {
                 bail!("NaN")
             }
         }
+        NilTree::Num(n) => *n,
     })
 }
 

src/parser.rs

@@ -20,7 +20,6 @@ use regex::Regex;
 
 use crate::{
     atoms::Atom,
-    extended_to_core::num_to_core,
     lang::{Block, Expression, Prog, ProgName, Statement},
     variables::VarName,
 };
@@ -325,7 +324,7 @@ fn brackets_expr(s: &str) -> IResult<&str, Expression, VerboseError<&str>> {
 
 fn atom_expr(s: &str) -> IResult<&str, Expression, VerboseError<&str>> {
     map_res(preceded(tag("@"), alt((alpha1, tag(":=")))), |atom| {
-        Atom::from_str(format!("@{atom}").as_str()).map(|atom| num_to_core(atom as u8 as usize))
+        Atom::from_str(format!("@{atom}").as_str()).map(|atom| Expression::Num(atom as u8 as usize))
     })(s)
 }
 
@@ -347,7 +346,7 @@ fn tree_literal_expr(s: &str) -> IResult<&str, Expression, VerboseError<&str>> {
 
 #[cfg(test)]
 mod tests {
-    use crate::extended_to_core::num_to_niltree;
+    use crate::extended_to_core::num_to_nils;
     use crate::parser::Expression;
     use crate::parser::{parse, Block, Prog, ProgName, VarName};
 
@@ -497,7 +496,7 @@ mod tests {
     #[test]
     fn test_stack_overflow() {
         let n = 1_000_000;
-        let n = num_to_niltree(n);
+        let n = num_to_nils(n);
         let m = n.clone();
         let _ = m == n;
     }