Add Sort ability

crates/compiler/builtins/roc/List.roc

@@ -69,6 +69,8 @@ module [
     walkBackwardsUntil,
     countIf,
     chunksOf,
+    Sort,
+    compare,
 ]
 
 import Bool exposing [Bool, Eq]
@@ -1324,3 +1326,10 @@ iterBackwardsHelp = \list, state, f, prevIndex ->
             Break b -> Break b
     else
         Continue state
+
+Sort implements
+    compare : a, a -> [LessThan, Equal, GreaterThan] where a implements Sort
+
+# INTERNAL COMPILER USE ONLY: used to lower calls to `compare` to structural
+# compare via the `Sort` low-level for derived types.
+structuralCompare : a, a -> [LessThan, Equal, GreaterThan]

crates/compiler/builtins/roc/main.roc

@@ -6,6 +6,7 @@ package [
     List,
     Dict,
     Set,
+    Sort
     Decode,
     Encode,
     Hash,

crates/compiler/can/src/builtins.rs

@@ -216,6 +216,7 @@ map_symbol_to_lowlevel_and_arity! {
     And; BOOL_AND; 2,
     Or; BOOL_OR; 2,
     Not; BOOL_NOT; 1,
+    Compare; LIST_STRUCTURAL_COMPARE; 2,
     BoxExpr; BOX_BOX_FUNCTION; 1,
     UnboxExpr; BOX_UNBOX; 1,
     Unreachable; LIST_UNREACHABLE; 1,

crates/compiler/derive_key/src/lib.rs

@@ -81,6 +81,7 @@ pub enum DeriveBuiltin {
     Decoder,
     Hash,
     IsEq,
+    Compare,
     ToInspector,
 }
 
@@ -93,6 +94,7 @@ impl TryFrom<Symbol> for DeriveBuiltin {
             Symbol::DECODE_DECODER => Ok(DeriveBuiltin::Decoder),
             Symbol::HASH_HASH => Ok(DeriveBuiltin::Hash),
             Symbol::BOOL_IS_EQ => Ok(DeriveBuiltin::IsEq),
+            Symbol::LIST_COMPARE => Ok(DeriveBuiltin::Compare),
             Symbol::INSPECT_TO_INSPECTOR => Ok(DeriveBuiltin::ToInspector),
             _ => Err(value),
         }
@@ -127,6 +129,13 @@ impl Derived {
                     Symbol::BOOL_STRUCTURAL_EQ,
                 ))
             }
+            DeriveBuiltin::Compare => {
+                // If obligation checking passes, we always lower derived implementations of
+                // `compare` to the `Compare` low-level, to be fulfilled by the backends.
+                Ok(Derived::SingleLambdaSetImmediate(
+                    Symbol::LIST_STRUCTURAL_COMPARE,
+                ))
+            }
             DeriveBuiltin::ToInspector => match FlatInspectable::from_var(subs, var) {
                 FlatInspectable::Immediate(imm) => Ok(Derived::Immediate(imm)),
                 FlatInspectable::Key(repr) => Ok(Derived::Key(DeriveKey::ToInspector(repr))),
@@ -161,6 +170,13 @@ impl Derived {
                     Symbol::BOOL_STRUCTURAL_EQ,
                 ))
             }
+            DeriveBuiltin::Compare => {
+                // If obligation checking passes, we always lower derived implementations of
+                // `compare` to the `Compare` low-level, to be fulfilled by the backends.
+                Ok(Derived::SingleLambdaSetImmediate(
+                    Symbol::LIST_STRUCTURAL_COMPARE,
+                ))
+            }
             DeriveBuiltin::ToInspector => {
                 match inspect::FlatInspectable::from_builtin_alias(symbol).unwrap() {
                     FlatInspectable::Immediate(imm) => Ok(Derived::Immediate(imm)),

crates/compiler/gen_llvm/src/llvm/lowlevel.rs

@@ -55,6 +55,7 @@ use crate::llvm::{
         LLVM_SUB_WITH_OVERFLOW,
     },
     refcounting::PointerToRefcount,
+    sort::generic_compare,
 };
 
 use super::{build::Env, convert::zig_dec_type};
@@ -1269,6 +1270,20 @@ pub(crate) fn run_low_level<'a, 'ctx>(
             let bool_val = env.builder.new_build_not(arg.into_int_value(), "bool_not");
             BasicValueEnum::IntValue(bool_val)
         }
+        Compare => {
+            // Sort.compare : elem, elem -> [LessThan, Equal, GreaterThan]
+            arguments_with_layouts!((lhs_arg, lhs_layout), (rhs_arg, rhs_layout));
+
+            generic_compare(
+                env,
+                layout_interner,
+                layout_ids,
+                lhs_arg,
+                rhs_arg,
+                lhs_layout,
+                rhs_layout,
+            )
+        }
         Hash => {
             unimplemented!()
         }

crates/compiler/gen_llvm/src/llvm/mod.rs

@@ -9,6 +9,7 @@ pub mod externs;
 mod intrinsics;
 mod lowlevel;
 pub mod refcounting;
+pub mod sort;
 
 mod align;
 mod erased;