SIGNATURE StringReduce[to]

-- reductions of strings

-- Parameter
SORT to

IMPORT String ONLY string       
       Char ONLY char

FUN / \ : (char ** to -> to) ** to ** string -> to              
        -- (o, e) / s
        -- reduce s from left (right) by o with value e as initial 
        -- 2nd argument.
        -- informally:
        -- (o / e)(<a, b,..., y, z>) == a o (b o (...(y o (z o e))...))
        -- (o \ e)(<a, b,..., y, z>) == z o (y o (...(b o (a o e))...))

-- old fashioned
FUN / \ : (char ** to -> to) ** to -> string -> to              
        --  (o / e)(s) == (o, e) / s