[ReleaseCandidat]

Actually the most important step of parsers (as even non-incremental, slow (or better: not fast) parsers are fast enough) is error recovery (error resilience) from syntax errors (mostly half written or half deleted code). What is time consuming is e.g. type-checking. Semantic checking in general, like exhaustiveness checks of pattern matches, syntax checking is fast.

[dboreham]

In the days of punched cards error recovery was important.