[[ Bug 20430 ]] Swap LCB exponentiation and unary operator precedence

livecodeali · livecodeali · commit 1fae053a0fdd · 2018-03-02T20:58:54.000Z
diff --git a/builder/release_notes_builder.livecodescript b/builder/release_notes_builder.livecodescript
@@ -407,6 +407,7 @@ private command BaseCreate
    BaseCreateOverview
    BaseCreateIssues
    
+   MarkdownAppend "notes", BaseReadFile("breaking_changes")
    MarkdownAppend "notes", BaseReadFile("platforms")
    MarkdownAppend "notes", BaseReadFile("setup")
    MarkdownAppend "notes", BaseReadFile("proposed_changes")
diff --git a/docs/lcb/notes/20430.md b/docs/lcb/notes/20430.md
@@ -0,0 +1,9 @@
+# LiveCode Builder Standard Library
+
+## Mathematical Operator Precedence
+
+* The exponentiation operator `^` now has higher precedence than
+  unary minus, meaning for example that -1^2 evaluates to -1 rather
+  than 1, as it does in LiveCode Script.
+
+# [20430] Exponentiation should have higher precedence than unary minus
diff --git a/docs/notes-base/breaking_changes.md b/docs/notes-base/breaking_changes.md
@@ -0,0 +1,16 @@
+# Breaking changes
+
+## LiveCode Builder
+
+### Exponentiation operator precedence
+Prior to this release, exponentiation had lower precedence that unary 
+minus. In order to write code that operates as expected in both this 
+release and previous releases, please use parentheses where appropriate.
+
+Using lc-compile tool in LiveCode 9:
+	
+	-1^2 = -1
+	
+Using lc-compile tool in LiveCode 8:
+	
+	-1^2 = 1
diff --git a/docs/specs/lcb-precedence.md b/docs/specs/lcb-precedence.md
@@ -31,10 +31,10 @@ Lower precedence numbers are more tightly-binding.
 |       | subscript         | `tList[1]`, `tArray["key"]`   |
 | 3     | property          | `the paint of this canvas`    |
 |       | subscript chunk   | `char 2 of tString`           |
-| 4     | conversion        | `tString parsed as number`    |
 |       | function chunk    | `the offset of "o" in "foo"`  |
-| 5     | modifier          | `-tNum`, `bitwise not`        |
-| 6     | exponentiation    | `^`                           |
+| 4     | conversion        | `tString parsed as number`    |
+| 5     | exponentiation    | `^`                           |
+| 6     | modifier          | `-tNum`, `bitwise not`        |
 | 7     | multiplication    | `/`,`*`,`mod`, `div`          |
 | 8     | addition          | `+`, `-`                      |
 |       | concatenation     | `&`, `&&`                     |
@@ -49,3 +49,7 @@ Lower precedence numbers are more tightly-binding.
 | 16    | logical and       | `Foo() and Bar()`             |
 | 17    | logical or        | `Foo() or Bar()`              |
 | 18    | sequence          | `,`                           |
+
+>**Important:** Prior to LiveCode 9, exponentiation and modifier 
+> precedence were reversed. In order to write code that operates as 
+> expected in both LC 9 and 8, please use parentheses where appropriate.
diff --git a/tests/lcb/stdlib/math.lcb b/tests/lcb/stdlib/math.lcb
@@ -47,9 +47,9 @@ public handler TestRound()
 end handler
 
 public handler TestPow()
-	test "pow (-ve, -ve)" when -2 ^ -2 is 0.25
+	test "pow (-ve, -ve)" when (-2) ^ -2 is 0.25
 	test "pow (-ve, +ve)" when (-2) ^ 2 is 4
-	test "pow (-ve, +ve)" when -2 ^ 3 is -8
+	test "pow (-ve, +ve)" when (-2) ^ 3 is -8
 	test "pow (+ve, -ve)" when 2 ^ -2 is 0.25
 	test "pow (+ve, +ve)" when 2 ^ 2 is 4
 	test "pow (0, 1)" when 0 ^ 1 is 0
@@ -66,8 +66,14 @@ public handler TestPowDomain()
 end handler
 
 public handler TestPowPrecedence()
-	test "pow vs. unary−" when -2 ^ 2 is 4
-	test "pow vs. unary−" when -2 ^ 0 is 1
+	test "pow vs. -" when 0-1^2 is -1
+	test "pow vs. -" when -1^2 is -1
+	test "pow vs. -" when 0-(1^2) is -1
+	test "pow vs. -" when -(1^2) is -1
+	test "pow vs. -" when 0-(1^2) is -1
+	test "pow vs. -" when -(1)^2 is -1
+	test "pow vs. -" when 0-(1)^2 is -1
+	test "pow vs. -" when (-1)^2 is 1
 end handler
 
 public handler TestLog10()
diff --git a/toolchain/lc-compile/src/syntax.g b/toolchain/lc-compile/src/syntax.g
@@ -294,13 +294,13 @@
 
     'rule' MapSyntaxPrecedence(property -> 3)
     'rule' MapSyntaxPrecedence(subscriptchunk -> 3)
+    'rule' MapSyntaxPrecedence(functionchunk -> 3)
 
     'rule' MapSyntaxPrecedence(conversion -> 4)
-    'rule' MapSyntaxPrecedence(functionchunk -> 3)
 
-    'rule' MapSyntaxPrecedence(modifier -> 5)
+    'rule' MapSyntaxPrecedence(exponentiation -> 5)
 
-    'rule' MapSyntaxPrecedence(exponentiation -> 6)
+    'rule' MapSyntaxPrecedence(modifier -> 6)
 
     'rule' MapSyntaxPrecedence(multiplication -> 7)
 
