ISBN13 check digit: Difference between revisions
→{{header|Standard ML}}: alternate SML version
Langurmonkey (talk | contribs) |
(→{{header|Standard ML}}: alternate SML version) |
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=={{header|Standard ML}}==
===Easy to read version===
<syntaxhighlight lang="sml">local▼
<syntaxhighlight lang="sml">(* these type decorations are optional, you could just as well put:
fun isValidISBN s =
*)
fun isValidISBN (s : string) : bool =
let
val digits = List.filter Char.isDigit (explode s)
val nums = map (fn x => ord x - ord #"0") digits
val len = length nums
fun sumISBN [] = raise Domain
| sumISBN [x] = x
| sumISBN (x1::x2::xs) = x1 + 3*x2 + sumISBN xs
in
len = 13 andalso sumISBN nums mod 10 = 0
end
val test = ["978-1734314502", "978-1734314509",
"978-1788399081", "978-1788399083"]
fun printTest (s : string) : unit =
(print s; print (if isValidISBN s then ": good\n" else ": bad\n"))
fun main () = app printTest test</syntaxhighlight>
===Original version===
fun check (c, p as (m, n)) =
if Char.isDigit c then
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