[Git][ghc/ghc][wip/negative-literals] Improve NegativeLiterals (#18022, GHC Proposal #344)
Vladislav Zavialov
gitlab at gitlab.haskell.org
Thu Jul 23 19:10:33 UTC 2020
Vladislav Zavialov pushed to branch wip/negative-literals at Glasgow Haskell Compiler / GHC
Commits:
5ccd9779 by Vladislav Zavialov at 2020-07-23T22:10:23+03:00
Improve NegativeLiterals (#18022, GHC Proposal #344)
Before this patch, NegativeLiterals used to parse x-1 as x (-1).
This may not be what the user expects, and now it is fixed:
x-1 is parsed as (-) x 1.
We achieve this by the following requirement:
* When lexing a negative literal,
it must not be preceded by a 'closing token'.
This also applies to unboxed literals, e.g. -1#.
See GHC Proposal #229 for the definition of a closing token.
A nice consequence of this change is that -XNegativeLiterals becomes a
subset of -XLexicalNegation. In other words, enabling both of those
extensions has the same effect as enabling -XLexicalNegation alone.
- - - - -
7 changed files:
- compiler/GHC/Parser/Lexer.x
- docs/users_guide/8.12.1-notes.rst
- docs/users_guide/exts/negative_literals.rst
- − testsuite/tests/parser/should_compile/LexNegVsNegLit.hs
- + testsuite/tests/parser/should_compile/NegativeLiterals.hs
- + testsuite/tests/parser/should_compile/NegativeLiteralsNoExt.hs
- testsuite/tests/parser/should_compile/all.T
Changes:
=====================================
compiler/GHC/Parser/Lexer.x
=====================================
@@ -199,7 +199,6 @@ $docsym = [\| \^ \* \$]
-- normal signed numerical literals can only be explicitly negative,
-- not explicitly positive (contrast @exponent)
@negative = \-
- at signed = @negative ?
-- -----------------------------------------------------------------------------
@@ -531,12 +530,12 @@ $tab { warnTab }
ifExtension BinaryLiteralsBit } { tok_primint positive 2 3 binary }
0[oO] @numspc @octal \# / { ifExtension MagicHashBit } { tok_primint positive 2 3 octal }
0[xX] @numspc @hexadecimal \# / { ifExtension MagicHashBit } { tok_primint positive 2 3 hexadecimal }
- @negative @decimal \# / { ifExtension MagicHashBit } { tok_primint negative 1 2 decimal }
- @negative 0[bB] @numspc @binary \# / { ifExtension MagicHashBit `alexAndPred`
+ @negative @decimal \# / { negHashLitPred } { tok_primint negative 1 2 decimal }
+ @negative 0[bB] @numspc @binary \# / { negHashLitPred `alexAndPred`
ifExtension BinaryLiteralsBit } { tok_primint negative 3 4 binary }
- @negative 0[oO] @numspc @octal \# / { ifExtension MagicHashBit } { tok_primint negative 3 4 octal }
+ @negative 0[oO] @numspc @octal \# / { negHashLitPred } { tok_primint negative 3 4 octal }
@negative 0[xX] @numspc @hexadecimal \#
- / { ifExtension MagicHashBit } { tok_primint negative 3 4 hexadecimal }
+ / { negHashLitPred } { tok_primint negative 3 4 hexadecimal }
@decimal \# \# / { ifExtension MagicHashBit } { tok_primword 0 2 decimal }
0[bB] @numspc @binary \# \# / { ifExtension MagicHashBit `alexAndPred`
@@ -546,8 +545,11 @@ $tab { warnTab }
-- Unboxed floats and doubles (:: Float#, :: Double#)
-- prim_{float,double} work with signed literals
- @signed @floating_point \# / { ifExtension MagicHashBit } { tok_frac 1 tok_primfloat }
- @signed @floating_point \# \# / { ifExtension MagicHashBit } { tok_frac 2 tok_primdouble }
+ @floating_point \# / { ifExtension MagicHashBit } { tok_frac 1 tok_primfloat }
+ @floating_point \# \# / { ifExtension MagicHashBit } { tok_frac 2 tok_primdouble }
+
+ @negative @floating_point \# / { negHashLitPred } { tok_frac 1 tok_primfloat }
+ @negative @floating_point \# \# / { negHashLitPred } { tok_frac 2 tok_primdouble }
}
-- Strings and chars are lexed by hand-written code. The reason is
@@ -1192,8 +1194,8 @@ atEOL _ _ _ (AI _ buf) = atEnd buf || currentChar buf == '\n'
-- Check if we should parse a negative literal (e.g. -123) as a single token.
negLitPred :: AlexAccPred ExtsBitmap
negLitPred =
- negative_literals `alexOrPred`
- (lexical_negation `alexAndPred` prefix_minus)
+ prefix_minus `alexAndPred`
+ (negative_literals `alexOrPred` lexical_negation)
where
negative_literals = ifExtension NegativeLiteralsBit
@@ -1202,14 +1204,33 @@ negLitPred =
alexNotPred (ifExtension NoLexicalNegationBit)
prefix_minus =
- -- The condition for a prefix occurrence of an operator is:
- --
- -- not precededByClosingToken && followedByOpeningToken
- --
- -- but we don't check followedByOpeningToken here as it holds
- -- simply because we immediately lex a literal after the minus.
+ -- Note [prefix_minus in negLitPred and negHashLitPred]
+ alexNotPred precededByClosingToken
+
+-- Check if we should parse an unboxed negative literal (e.g. -123#) as a single token.
+negHashLitPred :: AlexAccPred ExtsBitmap
+negHashLitPred = prefix_minus `alexAndPred` magic_hash
+ where
+ magic_hash = ifExtension MagicHashBit
+ prefix_minus =
+ -- Note [prefix_minus in negLitPred and negHashLitPred]
alexNotPred precededByClosingToken
+{- Note [prefix_minus in negLitPred and negHashLitPred]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We want to parse -1 as a single token, but x-1 as three tokens.
+So in negLitPred (and negHashLitPred) we require that we have a prefix
+occurrence of the minus sign. See Note [Whitespace-sensitive operator parsing]
+for a detailed definition of a prefix occurrence.
+
+The condition for a prefix occurrence of an operator is:
+
+ not precededByClosingToken && followedByOpeningToken
+
+but we don't check followedByOpeningToken when parsing a negative literal.
+It holds simply because we immediately lex a literal after the minus.
+-}
+
ifExtension :: ExtBits -> AlexAccPred ExtsBitmap
ifExtension extBits bits _ _ _ = extBits `xtest` bits
=====================================
docs/users_guide/8.12.1-notes.rst
=====================================
@@ -224,6 +224,13 @@ Language
f = (- x) -- operator section
c = (-x) -- negation
+* The behavior of :extension:`NegativeLiterals` changed, and now we require
+ that a negative literal must not be preceded by a closing token (see
+ `GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__
+ for the definition of a closing token). In other words, we parse ``f -123``
+ as ``f (-123)``, but ``x-123`` as ``(-) x 123``. Before this amendment,
+ :extension:`NegativeLiterals` caused ``x-123`` to be parsed as ``x(-123)``.
+
Compiler
~~~~~~~~
=====================================
docs/users_guide/exts/negative_literals.rst
=====================================
@@ -24,9 +24,11 @@ will elicit an unexpected integer-literal-overflow message.
Whitespace can be inserted, as in ``- 123``, to force interpretation
as two tokens.
-One pitfall is that with :extension:`NegativeLiterals`, ``x-1`` will
-be parsed as ``x`` applied to the argument ``-1``, which is usually
-not what you want. ``x - 1`` or even ``x- 1`` can be used instead
-for subtraction. To avoid this, consider using :extension:`LexicalNegation`
-instead.
-
+In 8.12, the behavior of this extension changed, and now we require that a negative literal must not be preceded by a closing token (see
+`GHC Proposal #229 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0229-whitespace-bang-patterns.rst>`__
+for the definition of a closing token). In other words, we parse ``f -123`` as ``f (-123)``, but ``x-123`` as ``(-) x
+123``. Before this amendment, :extension:`NegativeLiterals` caused ``x-123`` to be parsed as ``x(-123)``.
+
+:extension:`NegativeLiterals` is a subset of :extension:`LexicalNegation`. That
+is, enabling both of those extensions has the same effect as enabling
+:extension:`LexicalNegation` alone.
=====================================
testsuite/tests/parser/should_compile/LexNegVsNegLit.hs deleted
=====================================
@@ -1,17 +0,0 @@
-{-# LANGUAGE NegativeLiterals, LexicalNegation #-}
-
-module LexNegVsNegLit where
-
--- NegativeLiterals specifies that we parse x-1 as x (-1), even though it's
--- considered a shortcoming.
---
--- LexicalNegation does not change that.
---
-b :: Bool
-b = even-1 -- parsed as: even (-1)
- -- so it is well-typed.
- --
- -- with LexicalNegation alone, we'd get (-) even 1,
- -- but NegativeLiterals takes precedence here.
-
--- See also: GHC Proposal #344
=====================================
testsuite/tests/parser/should_compile/NegativeLiterals.hs
=====================================
@@ -0,0 +1,57 @@
+{-# LANGUAGE NegativeLiterals, MagicHash, BinaryLiterals #-}
+
+module NegativeLiterals where
+
+import GHC.Exts
+
+------------------------------------
+-- Prefix occurrence of the minus --
+------------------------------------
+
+p1 :: Bool
+p1 = even -2 -- parsed as: even (-2)
+
+p2 :: Int
+p2 = I# -1# -- parsed as: I# (-1#)
+
+p3 :: Int
+p3 = floor -2.4 -- parsed as: floor (-2.4)
+
+p4 :: Float
+p4 = F# -0.01# -- parsed as: F# (-0.01#)
+
+p5 :: Double
+p5 = D# -0.01## -- parsed as: D# (-0.01##)
+
+p6 :: Bool
+p6 = even -0b10 -- parsed as: even (-2)
+ || even -0o10 -- parsed as: even (-8)
+ || even -0x10 -- parsed as: even (-16)
+
+-----------------------------------------
+-- Tight infix occurrence of the minus --
+-----------------------------------------
+
+ti1 :: Integer -> Integer
+ti1 x = x-2 -- parsed as: (-) x 1
+
+ti2 :: Int# -> Int#
+ti2 x = x-1# -- parsed as: (-) x 1#
+ where (-) = (-#)
+
+ti3 :: Double -> Double
+ti3 x = x-2.4 -- parsed as: (-) x 2.4
+
+ti4 :: Float# -> Float#
+ti4 x = x-0.1# -- parsed as: (-) x 0.1#
+ where (-) = minusFloat#
+
+ti5 :: Double# -> Double#
+ti5 x = x-0.1## -- parsed as: (-) x 0.1##
+ where (-) = (-##)
+
+ti6 :: Integer -> [Integer]
+ti6 x =
+ [ x-0b10, -- parsed as: (-) x 2
+ x-0o10, -- parsed as: (-) x 8
+ x-0x10 ] -- parsed as: (-) x 16
=====================================
testsuite/tests/parser/should_compile/NegativeLiteralsNoExt.hs
=====================================
@@ -0,0 +1,39 @@
+{-# LANGUAGE NoNegativeLiterals, MagicHash, BinaryLiterals #-}
+
+-- Even when NegativeLiterals are disabled,
+-- we parse unboxed literals appropriately.
+module NegativeLiteralsNoExt where
+
+import GHC.Exts
+
+------------------------------------
+-- Prefix occurrence of the minus --
+------------------------------------
+
+p2 :: Int
+p2 = I# -1# -- parsed as: I# (-1#)
+
+p4 :: Float
+p4 = F# -0.01# -- parsed as: F# (-0.01#)
+
+p5 :: Double
+p5 = D# -0.01## -- parsed as: D# (-0.01##)
+
+-----------------------------------------
+-- Tight infix occurrence of the minus --
+-----------------------------------------
+
+ti2 :: Int# -> Int#
+ti2 x = x-1# -- parsed as: (-) x 1#
+ where (-) = (-#)
+
+ti3 :: Double -> Double
+ti3 x = x-2.4 -- parsed as: (-) x 2.4
+
+ti4 :: Float# -> Float#
+ti4 x = x-0.1# -- parsed as: (-) x 0.1#
+ where (-) = minusFloat#
+
+ti5 :: Double# -> Double#
+ti5 x = x-0.1## -- parsed as: (-) x 0.1##
+ where (-) = (-##)
=====================================
testsuite/tests/parser/should_compile/all.T
=====================================
@@ -153,7 +153,8 @@ test('proposal-229b', normal, compile, [''])
test('proposal-229d', normal, compile, [''])
test('proposal-229e', normal, compile, [''])
test('LexicalNegation', normal, compile, [''])
-test('LexNegVsNegLit', normal, compile, [''])
+test('NegativeLiterals', normal, compile, [''])
+test('NegativeLiteralsNoExt', normal, compile, [''])
# We omit 'profasm' because it fails with:
# Cannot load -prof objects when GHC is built with -dynamic
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5ccd97796a5963a6087dd81e2b519f70a3bf16cc
--
View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/5ccd97796a5963a6087dd81e2b519f70a3bf16cc
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