From d26524048e2cbe64d6766d4eb3832376f310ba34 Mon Sep 17 00:00:00 2001
From: microproofs <kwhitemsg@gmail.com>
Date: Sat, 13 Jan 2024 18:55:39 -0500
Subject: [PATCH] fix: headlist builtin on assoc lists implement chooseunit for
 0 args

---
 crates/aiken-lang/src/gen_uplc.rs         | 35 ++++++++++++++++-------
 crates/aiken-lang/src/gen_uplc/builder.rs | 19 ++++++------
 2 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/crates/aiken-lang/src/gen_uplc.rs b/crates/aiken-lang/src/gen_uplc.rs
index f6b3be2f..b4481f1e 100644
--- a/crates/aiken-lang/src/gen_uplc.rs
+++ b/crates/aiken-lang/src/gen_uplc.rs
@@ -3770,14 +3770,25 @@ impl<'a> CodeGenerator<'a> {
                             builder::special_case_builtin(builtin, 0, vec![])
                         }
 
-                        DefaultFunction::FstPair
-                        | DefaultFunction::SndPair
-                        | DefaultFunction::HeadList => builder::undata_builtin(
-                            builtin,
-                            0,
-                            &constructor.tipo.return_type().unwrap(),
-                            vec![],
-                        ),
+                        DefaultFunction::FstPair | DefaultFunction::SndPair => {
+                            builder::undata_builtin(
+                                builtin,
+                                0,
+                                &constructor.tipo.return_type().unwrap(),
+                                vec![],
+                            )
+                        }
+
+                        DefaultFunction::HeadList
+                            if !constructor.tipo.return_type().unwrap().is_2_tuple() =>
+                        {
+                            builder::undata_builtin(
+                                builtin,
+                                0,
+                                &constructor.tipo.return_type().unwrap(),
+                                vec![],
+                            )
+                        }
 
                         DefaultFunction::MkCons | DefaultFunction::MkPairData => {
                             unimplemented!("MkCons and MkPairData should be handled by an anon function or using [] or ( a, b, .., z).\n")
@@ -4164,9 +4175,11 @@ impl<'a> CodeGenerator<'a> {
                         builder::special_case_builtin(&func, count, arg_vec)
                     }
 
-                    DefaultFunction::FstPair
-                    | DefaultFunction::SndPair
-                    | DefaultFunction::HeadList => {
+                    DefaultFunction::FstPair | DefaultFunction::SndPair => {
+                        builder::undata_builtin(&func, count, tipo, arg_vec)
+                    }
+
+                    DefaultFunction::HeadList if !tipo.is_2_tuple() => {
                         builder::undata_builtin(&func, count, tipo, arg_vec)
                     }
 
diff --git a/crates/aiken-lang/src/gen_uplc/builder.rs b/crates/aiken-lang/src/gen_uplc/builder.rs
index 017e7eb4..b5567d1a 100644
--- a/crates/aiken-lang/src/gen_uplc/builder.rs
+++ b/crates/aiken-lang/src/gen_uplc/builder.rs
@@ -1543,7 +1543,14 @@ pub fn special_case_builtin(
     mut args: Vec<Term<Name>>,
 ) -> Term<Name> {
     match func {
-        DefaultFunction::IfThenElse
+        DefaultFunction::ChooseUnit if count > 0 => {
+            let term = args.pop().unwrap();
+            let unit = args.pop().unwrap();
+
+            term.lambda("_").apply(unit)
+        }
+        DefaultFunction::ChooseUnit
+        | DefaultFunction::IfThenElse
         | DefaultFunction::ChooseList
         | DefaultFunction::ChooseData
         | DefaultFunction::Trace => {
@@ -1580,16 +1587,6 @@ pub fn special_case_builtin(
 
             term
         }
-        DefaultFunction::ChooseUnit => {
-            if count == 0 {
-                unimplemented!("Honestly, why are you doing this?")
-            } else {
-                let term = args.pop().unwrap();
-                let unit = args.pop().unwrap();
-
-                term.lambda("_").apply(unit)
-            }
-        }
         DefaultFunction::UnConstrData => {
             let mut term: Term<Name> = (*func).into();