From 4204d21ac03940c27b137ef2a66659af45f14790 Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Thu, 14 Nov 2019 23:30:07 +0100
Subject: [PATCH 1/2] Desugar pizza into Apply

---
 src/can/operator.rs | 27 ++++++++++++++++++++++++++-
 tests/test_infer.rs | 26 +++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/src/can/operator.rs b/src/can/operator.rs
index d16b763ade..6350912932 100644
--- a/src/can/operator.rs
+++ b/src/can/operator.rs
@@ -199,7 +199,32 @@ pub fn desugar<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a Loca
                 let value = match loc_op.value {
                     Pizza => {
                         // Rewrite the Pizza operator into an Apply
-                        panic!("TODO desugar |> operator into an Apply");
+
+                        match &right.value {
+                            Apply(function, arguments, _called_via) => {
+                                let mut args = Vec::with_capacity_in(1 + arguments.len(), arena);
+
+                                args.push(*arena.alloc(left));
+
+                                for arg in arguments {
+                                    args.push(arg);
+                                }
+
+                                Apply(function, args, CalledVia::BinOp(Pizza))
+                            }
+                            expr => {
+                                // e.g. `1 |> (if b then (\a -> a) else (\c -> c))`
+                                let mut args = Vec::with_capacity_in(1, arena);
+                                args.push(*arena.alloc(left));
+
+                                let function = arena.alloc(Located {
+                                    value: expr.clone(),
+                                    region: right.region,
+                                });
+
+                                Apply(function, args, CalledVia::BinOp(Pizza))
+                            }
+                        }
                     }
                     binop => {
                         // This is a normal binary operator like (+), so desugar it
diff --git a/tests/test_infer.rs b/tests/test_infer.rs
index 17898273c1..c6c8265d51 100644
--- a/tests/test_infer.rs
+++ b/tests/test_infer.rs
@@ -492,6 +492,31 @@ mod test_infer {
         );
     }
 
+    #[test]
+    fn pizza_desugar() {
+        infer_eq(
+            indoc!(
+                r#"
+                1 |> (\a -> a)
+                "#
+            ),
+            "Int",
+        );
+    }
+
+    #[test]
+    fn pizza_desugar_two_arguments() {
+        infer_eq(
+            indoc!(
+                r#"
+                always = \a b -> a
+
+                1 |> always "foo" 
+                "#
+            ),
+            "Int",
+        );
+    }
     //     #[test]
     //     fn identity() {
     //         infer_eq(
@@ -624,5 +649,4 @@ mod test_infer {
             "Int",
         );
     }
-
 }

From 1ea0264174ce1b254aa4a2b6d71d50edf645acf3 Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Fri, 15 Nov 2019 12:18:06 +0100
Subject: [PATCH 2/2] changes after review

trust the borrow checker: reallocation of Expr is not needed
---
 src/can/operator.rs | 6 +++---
 tests/test_infer.rs | 3 ++-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/can/operator.rs b/src/can/operator.rs
index 6350912932..255d2b128a 100644
--- a/src/can/operator.rs
+++ b/src/can/operator.rs
@@ -204,7 +204,7 @@ pub fn desugar<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a Loca
                             Apply(function, arguments, _called_via) => {
                                 let mut args = Vec::with_capacity_in(1 + arguments.len(), arena);
 
-                                args.push(*arena.alloc(left));
+                                args.push(left);
 
                                 for arg in arguments {
                                     args.push(arg);
@@ -232,8 +232,8 @@ pub fn desugar<'a>(arena: &'a Bump, loc_expr: &'a Located<Expr<'a>>) -> &'a Loca
                         let (module_parts, name) = desugar_binop(&binop, arena);
                         let mut args = Vec::with_capacity_in(2, arena);
 
-                        args.push(*arena.alloc(left));
-                        args.push(*arena.alloc(right));
+                        args.push(left);
+                        args.push(right);
 
                         let loc_expr = arena.alloc(Located {
                             value: Expr::Var(module_parts, name),
diff --git a/tests/test_infer.rs b/tests/test_infer.rs
index c6c8265d51..79165f6146 100644
--- a/tests/test_infer.rs
+++ b/tests/test_infer.rs
@@ -511,7 +511,7 @@ mod test_infer {
                 r#"
                 always = \a b -> a
 
-                1 |> always "foo" 
+                1 |> always "foo"
                 "#
             ),
             "Int",
@@ -649,4 +649,5 @@ mod test_infer {
             "Int",
         );
     }
+
 }