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[ABNF] Make the lexical grammar slightly less ambiguous.

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Before this commit, 'true' and 'false' were both keywords and boolean literals,
making the grammar slightly more ambiguous than it needs to be. This manifests
in the formal specification of lexing and parsing, which would need an
additional extra-grammatical predicate requiring 'true' and 'false' to be
boolean literals and not keywords. By making 'true' and 'false' just boolean
literals, we obviate that need.

Extend the comment about identifiers and package names not being keywords or
aleo1... to also exclude boolean literals.

This is similar to the grammar of Java, in which 'true', 'false', and 'null' are
not keywords.

This does not necessitate any change to the lexer/parser, which already performs
its own procedural disambiguation of this and other aspects of the grammar.
This commit is contained in:
Alessandro Coglio 2021-07-26 21:12:30 -07:00
parent a73bc73750
commit ecadb3c321
1 changed files with 3 additions and 4 deletions
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7
grammar/abnf-grammar.txt
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@ -395,7 +395,6 @@ keyword = %s"address"
/ %s"console"
/ %s"const"
/ %s"else"
/ %s"false"
/ %s"field"
/ %s"for"
/ %s"function"
@ -416,7 +415,6 @@ keyword = %s"address"
/ %s"self"
/ %s"static"
/ %s"string"
/ %s"true"
/ %s"u8"
/ %s"u16"
/ %s"u32"
@ -448,7 +446,8 @@ hexadecimal-digit = digit / "a" / "b" / "c" / "d" / "e" / "f"
; because that is used for address literals:
; this is another extra-grammatical requirement.
identifier = letter *( letter / digit / "_" ) ; but not a keyword or aleo1...
identifier = letter *( letter / digit / "_" )
; but not a keyword or a boolean literal or aleo1...
; A package name consists of one or more segments separated by single dashes,
; where each segment is a non-empty sequence of lowercase letters and digits.
@ -457,7 +456,7 @@ identifier = letter *( letter / digit / "_" ) ; but not a keyword or aleo1...
package-name = lowercase-letter *( lowercase-letter / digit )
*( "-" 1*( lowercase-letter / digit ) )
; but not a keyword or aleo1...
; but not a keyword or a boolean literal or aleo1...
; Note that, grammatically, identifiers are also package names.
; They are disambiguated from context, based on the syntactic grammar.