fix(parser): accept optional DO after WHILE condition

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

9 files changed, 14 insertions, 15 deletions

diff --git a/AGENTS/PITFALLS.md b/AGENTS/PITFALLS.md
index bae6bd3..ec5d034 100644
--- a/AGENTS/PITFALLS.md
+++ b/AGENTS/PITFALLS.md
@@ -119,4 +119,4 @@ NEW and class inheritance. Compiler fixtures now live in `tests/` (see TESTING.m
 Nightly CI runs the compiler suites, packaged EMBEDDED smoke checks and existing
 plugin tests. The initial standard conflicts and missing diagnostic locations are fixed on
 Linux.
-WHILE uses the standard header without DO; old WHILE DO programs must be migrated.
+WHILE accepts both the standard header without DO and the older WHILE DO form.
diff --git a/lib/Parser/ParserControlFlow.cc b/lib/Parser/ParserControlFlow.cc
index afa8bd8..1cbedcd 100644
--- a/lib/Parser/ParserControlFlow.cc
+++ b/lib/Parser/ParserControlFlow.cc
@@ -54,6 +54,8 @@ std::unique_ptr<StmtAST> Parser::ParseWhileStmt() {
     auto Cond = ParseExpression();
     if (!Cond) return nullptr;
 
+    if (CurTok == tok_identifier && Lex.IdentifierStr == "DO") getNextToken();
+
     std::vector<std::unique_ptr<StmtAST>> Body = ParseBlock({tok_endwhile});
 
     if (CurTok != tok_endwhile) {
diff --git a/tests/i/while-do/case.json b/tests/i/while-do/case.json
new file mode 100644
index 0000000..0967ef4
--- /dev/null
+++ b/tests/i/while-do/case.json
@@ -0,0 +1 @@
+{}
diff --git a/tests/i/while-do/expected.txt b/tests/i/while-do/expected.txt
new file mode 100644
index 0000000..0cfbf08
--- /dev/null
+++ b/tests/i/while-do/expected.txt
@@ -0,0 +1 @@
+2
diff --git a/tests/i/while-do/notes.md b/tests/i/while-do/notes.md
new file mode 100644
index 0000000..01e389c
--- /dev/null
+++ b/tests/i/while-do/notes.md
@@ -0,0 +1,3 @@
+# while-do
+
+The legacy WHILE DO spelling and the standard WHILE spelling are both accepted. X advances from 0 through 1 to 2, then the loop stops.
diff --git a/tests/i/while-do/program.cps b/tests/i/while-do/program.cps
new file mode 100644
index 0000000..58d6319
--- /dev/null
+++ b/tests/i/while-do/program.cps
@@ -0,0 +1,6 @@
+DECLARE X : INTEGER
+X <- 0
+WHILE X < 2 DO
+    X <- X + 1
+ENDWHILE
+OUTPUT X
diff --git a/tests/iii/while-do-rejected/case.json b/tests/iii/while-do-rejected/case.json
deleted file mode 100644
index 9908d5e..0000000
--- a/tests/iii/while-do-rejected/case.json
+++ /dev/null
@@ -1,8 +0,0 @@
-{
-  "errors": [
-    {
-      "reason": "Expected\\ '<\\-'\\ after\\ identifier\\ 'DO'",
-      "line": 1
-    }
-  ]
-}
diff --git a/tests/iii/while-do-rejected/notes.md b/tests/iii/while-do-rejected/notes.md
deleted file mode 100644
index ed669b5..0000000
--- a/tests/iii/while-do-rejected/notes.md
+++ /dev/null
@@ -1,3 +0,0 @@
-# while-do-rejected
-
-The compiler must reject this program: Expected '<-' after identifier 'DO'. The diagnostic must identify line 1; compilation must preserve existing output.
diff --git a/tests/iii/while-do-rejected/program.cps b/tests/iii/while-do-rejected/program.cps
deleted file mode 100644
index b733e21..0000000
--- a/tests/iii/while-do-rejected/program.cps
+++ /dev/null
@@ -1,3 +0,0 @@
-WHILE FALSE DO
-    OUTPUT 1
-ENDWHILE