My attempt to calculating the runtime of all the videos in a list.

justforfun.sml

exception NoAnswer;

val files : string list = ["Signatures and Hiding Things (7-02).mp4",
                           "A Module Example (11-06).mp4",
                           "Signatures for Our Example (11-03).mp4",
                           "Signature Matching (4-03).mp4",
                           "An Equivalent Structure (6-38).mp4",
                           "Another Equivalent Structure (9-01).mp4",
                           "Different Modules Define Different Types (3-32).mp4",
                           "Equivalent Functions (8-41).mp4",
                           "Standard Equivalences (10-01).mp4",
                           "Equivalence Versus Performance (6-00).mp4",
                           "Section Introduction (1-45).mp4",
                           "What is Type Inference (5-37).mp4",
                           "ML Type Inference (6-09).mp4",
                           "Type Inference Examples (10-27).mp4",
                           "Polymorphic Examples (10-52).mp4",
                           "Optional- The Value Restriction and  Other Type-Inference Challenges (9-53).mp4",
                           "Mutual Recursion (9-45).mp4",
                           "Modules for Namespace Management (6-25).mp4"]

fun substring c1 c2 s =
    let
        val match1 = (List.last (String.tokens (fn c => c=c1) s))
        val match2 = hd (String.tokens (fn c => c=c2) match1)
    in
        match2
    end

val get_time_st = substring #"(" #")";

fun get_time ts =
    let
        val time = String.tokens (fn c => c= #"-") ts
        val min = hd time
        val sec = List.last time
    in
        (min,sec)
    end

fun get_seconds (m,s) =
    case (Int.fromString m, Int.fromString s) of
        (SOME x, SOME y) => (x * 60) + y
     |  (_,_) => raise NoAnswer

fun sum xs =
    foldl (fn (x,acc) => x+acc) 0 xs

fun session_time x =
    (x div 3600, x div 60 mod 60)

val total_session =  (session_time o sum) (map (get_seconds o get_time o get_time_st) files) handle NoAnwer => (0,0);

(* Output;;=> val total_session = (2,18) : int * int*)