feat: add mux and foldhood_plus builtins

Author: lm98

src/core/lang/builtins.rs

@@ -0,0 +1,32 @@
+use crate::core::lang::lang::{foldhood, mid, nbr};
+use crate::core::vm::round_vm::round_vm::RoundVM;
+
+pub fn mux<A, TH, EL>(vm: RoundVM, cond: bool, th: TH, el: EL) -> (RoundVM, A)
+    where
+        TH: Fn(RoundVM) -> (RoundVM, A),
+        EL: Fn(RoundVM) -> (RoundVM, A),
+{
+    if cond {
+        th(vm)
+    } else {
+        el(vm)
+    }
+}
+
+pub fn foldhood_plus<A: Copy + 'static, F, G, H>(vm: RoundVM, init: F, aggr: G, expr: H) -> (RoundVM, A)
+    where
+        F: Fn(RoundVM) -> (RoundVM, A) + Copy,
+        G: Fn(A, A) -> A,
+        H: Fn(RoundVM) -> (RoundVM, A) + Copy,
+{
+    foldhood(
+        vm,
+        init,
+        aggr,
+        |vm1| {
+            let (vm_, self_id) = mid(vm1);
+            let (vm__, nbr_id) = nbr(vm_, |vm2| mid(vm2));
+            mux(vm__, self_id == nbr_id, expr, init)
+        }
+    )
+}

src/core/lang/mod.rs

@@ -1,3 +1,4 @@
 pub mod lang;
 pub mod execution;
+pub mod builtins;
 mod test;