From 8e95712a161d8a4b0082ba5fe59a9f9026ba9974 Mon Sep 17 00:00:00 2001
From: "P. Oscar Boykin" <johnynek@users.noreply.github.com>
Date: Sun, 14 Oct 2018 17:09:06 -1000
Subject: [PATCH] Fix a bug with type param orders (#82)

* Fix a bug with type param orders

* use reverseMap to save one pass
---
 .../main/scala/org/bykn/bosatsu/Statement.scala    |  6 ++++--
 .../main/scala/org/bykn/bosatsu/rankn/Infer.scala  |  6 ++++++
 .../org/bykn/bosatsu/rankn/RankNInferTest.scala    | 14 ++++++++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/core/src/main/scala/org/bykn/bosatsu/Statement.scala b/core/src/main/scala/org/bykn/bosatsu/Statement.scala
index 722c0cc76..668608ad6 100644
--- a/core/src/main/scala/org/bykn/bosatsu/Statement.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/Statement.scala
@@ -230,7 +230,8 @@ sealed abstract class TypeDefinitionStatement extends Statement {
         val initVars = existingVars(argsType)
         val initState = ((initVars.toSet, initVars.reverse), 0L)
         val (((_, typeVars), _), params) = buildParams(argsType).run(initState).value
-        val typeParams = typeVars.map { tv =>
+        // we reverse to make sure we see in traversal order
+        val typeParams = typeVars.reverseMap { tv =>
           tv.toVar match {
             case b@Type.Var.Bound(_) => b
             case unexpected => sys.error(s"unexpectedly parsed a non bound var: $unexpected")
@@ -262,7 +263,8 @@ sealed abstract class TypeDefinitionStatement extends Statement {
         val initVars = existingVars(conArgs.toList.flatMap(_._2))
         val initState = ((initVars.toSet, initVars.reverse), 0L)
         val (((_, typeVars), _), constructors) = constructorsS.run(initState).value
-        val typeParams = typeVars.map { tv =>
+        // we reverse to make sure we see in traversal order
+        val typeParams = typeVars.reverseMap { tv =>
           tv.toVar match {
             case b@Type.Var.Bound(_) => b
             case unexpected => sys.error(s"unexpectedly parsed a non bound var: $unexpected")
diff --git a/core/src/main/scala/org/bykn/bosatsu/rankn/Infer.scala b/core/src/main/scala/org/bykn/bosatsu/rankn/Infer.scala
index ef5ba59f3..af31c3256 100644
--- a/core/src/main/scala/org/bykn/bosatsu/rankn/Infer.scala
+++ b/core/src/main/scala/org/bykn/bosatsu/rankn/Infer.scala
@@ -37,6 +37,12 @@ object Infer {
     }
 
 
+  /**
+   * The first element of the tuple are the the bound type
+   * vars for this type.
+   * the next are the types of the args of the constructor
+   * the final is the defined type this creates
+   */
   type Cons = (List[Type.Var], List[Type], Type.Const.Defined)
 
   case class Env(
diff --git a/core/src/test/scala/org/bykn/bosatsu/rankn/RankNInferTest.scala b/core/src/test/scala/org/bykn/bosatsu/rankn/RankNInferTest.scala
index 9efdcc4c0..c45c47cfd 100644
--- a/core/src/test/scala/org/bykn/bosatsu/rankn/RankNInferTest.scala
+++ b/core/src/test/scala/org/bykn/bosatsu/rankn/RankNInferTest.scala
@@ -415,6 +415,20 @@ main = Monad(optPure, optBind)
 """, "Monad[Opt]")
   }
 
+  test("def with type annotation and use the types inside") {
+   parseProgram("""#
+
+struct Pair(fst, snd)
+
+def fst(p: Pair[a, b]) -> a:
+  match p:
+    Pair(f, _):
+      f
+
+main = fst(Pair(1, "1"))
+""", "Int")
+  }
+
   test("test that we see some ill typed programs") {
   parseProgramIllTyped("""#