From 0552d676bfa6e6b009132c540ae822e8bd148b4a Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 17 Sep 2023 16:58:57 +0100
Subject: Disambiguate tuple expression statement from assignment

---
 .../java/org/shedlang/compiler/parser/Parser.java  | 29 +++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 17511bcc..44c132e7 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -301,7 +301,7 @@ public class Parser {
 
     static UntypedFunctionStatementNode parseFunctionStatement(TokenIterator<TokenType> tokens) {
         return switch (tokens.peek().tokenType()) {
-            case KEYWORD_ASSIGN, KEYWORD_VAL, KEYWORD_VAR, SYMBOL_HASH_PAREN_OPEN ->
+            case KEYWORD_ASSIGN, KEYWORD_VAL, KEYWORD_VAR ->
                 parseAssign(tokens);
 
             case KEYWORD_RETURN ->
@@ -310,11 +310,38 @@ public class Parser {
             case KEYWORD_WHILE ->
                 parseWhile(tokens);
 
+            case SYMBOL_HASH_PAREN_OPEN ->
+                parseFunctionStatementTuple(tokens);
+
             default ->
                 parseExpressionStatement(tokens);
         };
     }
 
+    private static UntypedFunctionStatementNode parseFunctionStatementTuple(
+        TokenIterator<TokenType> tokens
+    ) {
+        // We need to disambiguate destructuring assignments from
+        // tuple expression statements.
+
+        var offset = 0;
+        while (true) {
+            var token = tokens.peek(offset);
+            switch (token.tokenType()) {
+                case SYMBOL_HASH_PAREN_OPEN ->
+                    offset += 1;
+
+                case KEYWORD_ASSIGN, KEYWORD_VAL, KEYWORD_VAR -> {
+                    return parseAssign(tokens);
+                }
+
+                default -> {
+                    return parseExpressionStatement(tokens);
+                }
+            }
+        }
+    }
+
     private static UntypedExpressionNode parseIf(TokenIterator<TokenType> tokens) {
         var start = tokens.position();
 
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