[mrkeen]

Was the original blog post wrong?

[qsera]

were you validating during parsing before?

[instig007]

Validating during parsing is still parsing, there's a reason why `Alternative f` exists after all: you have to choose between branches of possibilities and falsehoods. Now consider that there's another kind of validation that happens outside of program boundaries (where broader-than-needed data is being constrained in a callee rather than the calling site) that should've been expresed as `Alternative f` during parsing instead. That's the main point of the article, but you seem to only focus on the literal occurence of the word "validation" here and there.