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oxe-i
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Mar 6, 2026
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| def plants (diagram : String) (student: String) : Vector Plant 4 := | ||
| let letters := diagram.toList | ||
| let first := 2 * ((student.toList)[0]!.val.toNat - 65) |
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You can use student.front to access the first letter in a String. Since Lean is not lazy, .toList is O(n).
oxe-i
reviewed
Mar 6, 2026
| let second := first + 1 | ||
| let third := (diagram.length + 1) / 2 + first | ||
| let fourth := third + 1 | ||
| let firstPlant := lookup letters[first]! |
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We can access individual Chars using String.Pos.get. In the version we are using, if we cast String to String.Slice and get startPos with, e.g., letters := diagram.toSlice.startPos, then we can use (letters.nextn first).get! to get the letter at position first.
I found that the Lean version we are using is right in the middle of an API change to the String type. In the latest version there is no need to cast String to String.Slice, this is done implicitly.
oxe-i
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