From 9d15f1601242707953864e687a261932a6bf84ea Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 29 Oct 2023 18:02:04 +0000
Subject: Support inferring return type from single return statement

---
 .../compiler/ast/typed/TypedFunctionBodyNode.java  |  5 +---
 .../ast/typed/TypedFunctionDefinitionNode.java     |  1 +
 .../ast/typed/TypedFunctionExpressionNode.java     |  1 +
 .../shedlang/compiler/typechecker/TypeChecker.java | 28 ++++++++++++++++++++--
 4 files changed, 29 insertions(+), 6 deletions(-)

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionBodyNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionBodyNode.java
index 415d4502..01225d71 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionBodyNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionBodyNode.java
@@ -8,6 +8,7 @@ import java.util.List;
 public record TypedFunctionBodyNode(
     FreeVariables freeVariables,
     TypedBlockNode block,
+    Type type,
     Source source
 ) implements TypedNode {
     public List<String> boundVariableNames() {
@@ -17,8 +18,4 @@ public record TypedFunctionBodyNode(
     public TypedFunctionStatementBehaviour behaviour() {
         return block.behaviour();
     }
-
-    public Type type() {
-        return block.type();
-    }
 }
diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionDefinitionNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionDefinitionNode.java
index 889b4fee..eb664e71 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionDefinitionNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionDefinitionNode.java
@@ -41,6 +41,7 @@ public record TypedFunctionDefinitionNode(
                 new TypedFunctionBodyNode(
                     freeVariables.build(),
                     new TypedBlockNode(body, boundVariableNames, Sources.NULL),
+                    Types.UNIT,
                     Sources.NULL
                 ),
                 type,
diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionExpressionNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionExpressionNode.java
index 401f4009..e11c35d0 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionExpressionNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedFunctionExpressionNode.java
@@ -37,6 +37,7 @@ public record TypedFunctionExpressionNode(
                 new TypedFunctionBodyNode(
                     freeVariables.build(),
                     new TypedBlockNode(body, boundVariableNames, Sources.NULL),
+                    Types.UNIT,
                     Sources.NULL
                 ),
                 type,
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index a68cc23c..b444a3a5 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -498,7 +498,10 @@ public class TypeChecker {
         var typedBody = bodyResult.value();
         context = bodyResult.context();
 
+        Type returnType;
         if (explicitReturnType.isPresent()) {
+            returnType = explicitReturnType.get();
+
             switch (typedBody.behaviour()) {
                 case TypedFunctionStatementBehaviour.BlockReturn blockReturn -> {
                     if (!isSubType(blockReturn.type(), explicitReturnType.get(), context)) {
@@ -529,12 +532,16 @@ public class TypeChecker {
                 case TypedFunctionStatementBehaviour.Continue continue_ -> {
                     switch (context.returnTypeState()) {
                         case ReturnTypeState.Explicit explicit -> {
-                            throw new UnsupportedOperationException("TODO");
+                            // TODO: better error
+                            throw new IllegalStateException();
                         }
                         case ReturnTypeState.ImplicitUnknown implicitUnknown -> {
                             // No explicit returns.
+                            returnType = Types.UNIT;
                         }
                         case ReturnTypeState.ImplicitLowerBound implicitLowerBound -> {
+                            returnType = implicitLowerBound.type();
+
                             checkIsSubType(
                                 Types.UNIT,
                                 implicitLowerBound.type(),
@@ -549,7 +556,23 @@ public class TypeChecker {
                     }
                 }
                 case TypedFunctionStatementBehaviour.Terminate terminate -> {
-                    throw new UnsupportedOperationException("TODO");
+                    switch (context.returnTypeState()) {
+                        case ReturnTypeState.Explicit explicit -> {
+                            // TODO: better error
+                            throw new IllegalStateException();
+                        }
+                        case ReturnTypeState.ImplicitUnknown implicitUnknown -> {
+                            // TODO: better error
+                            throw new IllegalStateException();
+                        }
+                        case ReturnTypeState.ImplicitLowerBound implicitLowerBound -> {
+                            returnType = implicitLowerBound.type();
+                        }
+                        case ReturnTypeState.NotInFunction notInFunction -> {
+                            // TODO: better error
+                            throw new IllegalStateException();
+                        }
+                    }
                 }
             }
         }
@@ -562,6 +585,7 @@ public class TypeChecker {
         var typed = new TypedFunctionBodyNode(
             freeVariables,
             typedBody,
+            returnType,
             typedBody.source()
         );
 
-- 
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