1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58

// Returns true if an integer is on the inputted character list and 

// false in all other conditions

let rec hasInteger l = 

    match l with

    | '~' :: c :: _ -> System.Char.IsDigit(c)

    | c :: _ -> System.Char.IsDigit(c)

    | [] -> false

// Returns a copy of the inputted character list 'l' with the next

// integer removed from the front of the list    

let rec skipInteger l = 

    match l with

    | '~' :: rest -> skipInteger(rest)

    | c :: rest -> 

        if (System.Char.IsDigit(c)) then skipInteger(rest) else c::rest

    | [] -> []

 

// Takes a list of characters and tries to return a string list of 

// token names 

let rec tokens s = 

    match s with

    | ',' :: rest -> "comma" :: tokens(rest)

    | '+' :: rest -> "plus" :: tokens(rest)

    | '-' :: rest -> "plus" :: tokens(rest)    

    | [] -> []

    | l -> if hasInteger(l) then "integer" :: tokens(skipInteger(l))

    // This very last function statement is failing on me with the 

    // error 

    // This expression was expected to have type string list but here

    // has type unit