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fix typo in macro-ambiguity.md
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@ -20,7 +20,7 @@ of this text is copied, and expanded upon in subsequent RFCs.
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character.
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- `simple NT`: a "meta-variable" non-terminal (further discussion below).
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- `complex NT`: a repetition matching non-terminal, specified via repetition
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operators (`\*`, `+`, `?`).
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operators (`*`, `+`, `?`).
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- `token`: an atomic element of a matcher; i.e. identifiers, operators,
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open/close delimiters, *and* simple NT's.
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- `token tree`: a tree structure formed from tokens (the leaves), complex
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@ -46,12 +46,12 @@ macro_rules! i_am_an_mbe {
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}
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```
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`(start $foo:expr $($i:ident),\* end)` is a matcher. The whole matcher is a
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`(start $foo:expr $($i:ident),* end)` is a matcher. The whole matcher is a
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delimited sequence (with open- and close-delimiters `(` and `)`), and `$foo`
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and `$i` are simple NT's with `expr` and `ident` as their respective fragment
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specifiers.
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`$(i:ident),\*` is *also* an NT; it is a complex NT that matches a
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`$(i:ident),*` is *also* an NT; it is a complex NT that matches a
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comma-separated repetition of identifiers. The `,` is the separator token for
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the complex NT; it occurs in between each pair of elements (if any) of the
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matched fragment.
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@ -72,7 +72,7 @@ its additional role as a fragment specifier; but it will be clear from context
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which interpretation is meant.)
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"SEP" will range over separator tokens, "OP" over the repetition operators
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`\*`, `+`, and `?`, "OPEN"/"CLOSE" over matching token pairs surrounding a
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`*`, `+`, and `?`, "OPEN"/"CLOSE" over matching token pairs surrounding a
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delimited sequence (e.g. `[` and `]`).
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Greek letters "α" "β" "γ" "δ" stand for potentially empty token-tree sequences.
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@ -110,7 +110,7 @@ of FIRST and FOLLOW are described later.
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1. For any separated complex NT in a matcher, `M = ... $(tt ...) SEP OP ...`,
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we must have `SEP` ∈ FOLLOW(`tt ...`).
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1. For an unseparated complex NT in a matcher, `M = ... $(tt ...) OP ...`, if
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OP = `\*` or `+`, we must have FOLLOW(`tt ...`) ⊇ FIRST(`tt ...`).
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OP = `*` or `+`, we must have FOLLOW(`tt ...`) ⊇ FIRST(`tt ...`).
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The first invariant says that whatever actual token that comes after a matcher,
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if any, must be somewhere in the predetermined follow set. This ensures that a
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@ -202,7 +202,7 @@ first token-tree (if any):
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* Let SEP\_SET(M) = { SEP } if SEP is present and ε ∈ FIRST(`tt ...`);
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otherwise SEP\_SET(M) = {}.
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* Let ALPHA\_SET(M) = FIRST(`α`) if OP = `\*` or `?` and ALPHA\_SET(M) = {} if
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* Let ALPHA\_SET(M) = FIRST(`α`) if OP = `*` or `?` and ALPHA\_SET(M) = {} if
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OP = `+`.
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* FIRST(M) = (FIRST(`tt ...`) \\ {ε}) ∪ SEP\_SET(M) ∪ ALPHA\_SET(M).
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@ -211,7 +211,7 @@ the possibility that the separator could be a valid first token for M, which
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happens when there is a separator defined and the repeated fragment could be
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empty. ALPHA\_SET(M) defines the possibility that the complex NT could be empty,
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meaning that M's valid first tokens are those of the following token-tree
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sequences `α`. This occurs when either `\*` or `?` is used, in which case there
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sequences `α`. This occurs when either `*` or `?` is used, in which case there
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could be zero repetitions. In theory, this could also occur if `+` was used with
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a potentially-empty repeating fragment, but this is forbidden by the third
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invariant.
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@ -339,7 +339,7 @@ represent simple nonterminals with the given fragment specifier.
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* FOLLOW(M), for any other M, is defined as the intersection, as t ranges over
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(LAST(M) \ {ε}), of FOLLOW(t).
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The tokens that can begin a type are, as of this writing, {`(`, `[`, `!`, `\*`,
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The tokens that can begin a type are, as of this writing, {`(`, `[`, `!`, `*`,
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`&`, `&&`, `?`, lifetimes, `>`, `>>`, `::`, any non-keyword identifier, `super`,
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`self`, `Self`, `extern`, `crate`, `$crate`, `_`, `for`, `impl`, `fn`, `unsafe`,
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`typeof`, `dyn`}, although this list may not be complete because people won't
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@ -347,9 +347,9 @@ always remember to update the appendix when new ones are added.
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Examples of FOLLOW for complex M:
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* FOLLOW(`$( $d:ident $e:expr )\*`) = FOLLOW(`$e:expr`)
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* FOLLOW(`$( $d:ident $e:expr )\* $(;)\*`) = FOLLOW(`$e:expr`) ∩ ANYTOKEN = FOLLOW(`$e:expr`)
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* FOLLOW(`$( $d:ident $e:expr )\* $(;)\* $( f |)+`) = ANYTOKEN
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* FOLLOW(`$( $d:ident $e:expr )*`) = FOLLOW(`$e:expr`)
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* FOLLOW(`$( $d:ident $e:expr )* $(;)*`) = FOLLOW(`$e:expr`) ∩ ANYTOKEN = FOLLOW(`$e:expr`)
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* FOLLOW(`$( $d:ident $e:expr )* $(;)* $( f |)+`) = ANYTOKEN
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### Examples of valid and invalid matchers
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