Add `while let` to the reference

Closes #17687

1 files changed, 12 insertions, 0 deletions

diff --git a/src/doc/reference.md b/src/doc/reference.md
index 261e5edcf66..4ad64576e15 100644
--- a/src/doc/reference.md
+++ b/src/doc/reference.md
@@ -3511,6 +3511,18 @@ of a condition expression it expects a refutable let statement. If the value of
 expression on the right hand side of the let statement matches the pattern, the corresponding
 block will execute, otherwise flow proceeds to the first `else` block that follows.
 
+### While let loops
+
+```{.ebnf .gram}
+while_let_expr : "while" "let" pat '=' expr '{' block '}' ;
+```
+
+A `while let` loop is semantically identical to a `while` loop but in place of a
+condition expression it expects a refutable let statement. If the value of the
+expression on the right hand side of the let statement matches the pattern, the
+loop body block executes and control returns to the pattern matching statement.
+Otherwise, the while expression completes.
+
 ### Return expressions
 
 ```{.ebnf .gram}