scheme function

[ecoswiss@yahoo.com (swiss)]

>hi,
>
>can any one tell me how to write a key function which takes a word as
>input and maps it to its key using the ctv character to vale mapping.
>where ctv("character to value mapping") maps 'a' to 1, 'b' to
>2,.....and 'z' to 26.
>for example 
>key("class")= ctv('c')* ctv('l')* ctv('a')* ctv('s')* ctv('s')
>           = 3 * 12* 1 * 19* 19 = 12996