Brian Wilkerson
f50c52f3dd
Change-Id: I8edb453f638223464ffb8563c8d4fe0dd6999991 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/269360 Reviewed-by: Samuel Rawlins <srawlins@google.com> Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
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The Token stream
The token stream is a doubly linked list with special 'EOF' tokens at the
beginning and end. The EOF token at the end points to itself as the next
token, and the one at the beginning points to itself as the previous token.
So, for a correctly formed token stream (which we routinely assume will always
be the case) neither previous nor next can ever return null. We can't
express that in the type system because those fields will be null temporarily
while the list is being built. As a result, the convention throughout the code
base, is to suffix those two getters with a bang (!) everywhere they're
invoked.
Tokens are typically accessed through the AST.