parser change: 'not' is always a unary operator; fixes #9574

4 files changed, 11 insertions, 1 deletions

diff --git a/changelog.md b/changelog.md
index 10d5510e6..f3ee98fb6 100644
--- a/changelog.md
+++ b/changelog.md
@@ -21,6 +21,8 @@
 
 - The `unchecked` pragma was removed, instead use `system.UncheckedArray`.
 - The undocumented ``#? strongSpaces`` parsing mode has been removed.
+- The `not` operator is now always a unary operator, this means that code like
+  ``assert not isFalse(3)`` compiles.
 
 
 #### Breaking changes in the standard library
diff --git a/compiler/lexer.nim b/compiler/lexer.nim
index 877369c2a..76cb88297 100644
--- a/compiler/lexer.nim
+++ b/compiler/lexer.nim
@@ -966,7 +966,7 @@ proc getPrecedence*(tok: TToken, strongSpaces: bool): int =
     of '?': result = 2
     else: considerAsgn(2)
   of tkDiv, tkMod, tkShl, tkShr: result = 9
-  of tkIn, tkNotin, tkIs, tkIsnot, tkNot, tkOf, tkAs: result = 5
+  of tkIn, tkNotin, tkIs, tkIsnot, tkOf, tkAs: result = 5
   of tkDotDot: result = 6
   of tkAnd: result = 4
   of tkOr, tkXor, tkPtr, tkRef: result = 3
diff --git a/doc/manual.rst b/doc/manual.rst
index e73806147..cb0194ba4 100644
--- a/doc/manual.rst
+++ b/doc/manual.rst
@@ -514,6 +514,9 @@ are used for other notational purposes.
 ``*:`` is as a special case treated as the two tokens `*`:tok: and `:`:tok:
 (to support ``var v*: T``).
 
+The ``not`` keyword is always a unary operator, ``a not b`` is parsed
+as ``a(not b)``, not as ``(a) not (b)``.
+
 
 Other tokens
 ------------
diff --git a/tests/parser/tprecedence.nim b/tests/parser/tprecedence.nim
index d586f14a3..cdf4ad3ee 100644
--- a/tests/parser/tprecedence.nim
+++ b/tests/parser/tprecedence.nim
@@ -19,3 +19,8 @@ proc foo[S, T](x: S, y: T): T = x & y
 proc bar[T](x: T): T = x
 
 echo "def".foo[:string, string]("abc"), " ", 4.bar[:int]
+
+# bug #9574
+proc isFalse(a: int): bool = false
+
+assert not isFalse(3)