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Comment by jb1991 | Hacker News Reader

jb1991

"1+1 sq ft in sq in="

The order of operations here is quite ambiguous. It’s not obvious even to a human reader how you would expect this to be interpreted.

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There is a perfectly cromulent grammar for a unit-aware calculator:

    <expression without units> [<unit> [in <unit>]]
    <expression with units> [in <unit>]

"1+2 feet in meters" and "1 foot + 1 meter" are both unambiguous. There is no order of operations in terms of how the units bind. The expression "1 foot + 1" is appropriately invalid.

Of course the appropriate care must be paid to interpreting "in" correctly as either a unit or a keyword.

I honestly can't tell what this would mean other than 2 square feet in inches. What's the other option?

Another option could be that it's ill-posed and should just return an error.

(1 sq ft in sq in) + 1?

Which sort of unit is a "sq ft in sq in" and why would they have coded it in the parser as one? It's only ambiguous if it's explicitly coded badly to induce ambiguity.

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