What is wrong with this situation?

Learning
1

I wrote a simple file, like this

type weeks = Mon | Tue | Wed | Thu | Fri | Sat | Sun
    
let day_of_week w =
   match w with
   | Mon -> 1
   | Tue -> 2
   | Wed -> 3
   | Thu -> 4
   | Fri -> 5
   | Sat -> 6
   | Sun -> 7

print_int (day_of_week Fri)

show me this message when compile it

I type the same code in utop is working normal.

And i change a little bit of code, it’s also done. like this

......
| Sun -> 7;;

.......

Following 2 pics is message on emacs

help me plz.
THANKS.

1 Like
2

also another situation.
a little similar like this

the code

let a = "This "
let b = " is "
let c = " a string"

print_string (a ^ b ^ c)

when compile it

☯~/code/ocaml☯ ocamlc -o e e.ml 
File "e.ml", line 3, characters 8-19:
3 | let c = " a string"
            ^^^^^^^^^^^
Error: This expression has type string
       This is not a function; it cannot be applied.

if i added ;; on each expression end, then the problem is gone.

what’s wrong with this?

3

You are correct you need to add a ;; to let the compiler know where the expression ends. Since there is no semicolon, the compiler thinks that you must be trying to call a function given by the previous expression.

type weeks = Mon | Tue | Wed | Thu | Fri | Sat | Sun

let day_of_week w =
  match w with
  | Mon -> 1
  | Tue -> 2
  | Wed -> 3
  | Thu -> 4
  | Fri -> 5
  | Sat -> 6
  | Sun -> 7
;;

print_int (day_of_week Fri)

should be what you want (the whitespace doesn’t matter and is probably what confused you in the original example)

4

Thanks. I understood it.

But i also have one confuse.
I almost did not see the semicolon in other OCaml code file.
This is a Bigest confuse point to me.

5

Newlines count as white space in OCaml. Thus, the compiler reads

let c = " a string"
print_string (a ^ b ^ c)

as

let c = " a string" print_string (a ^ b ^ c)

and protests that "a string" is not a function.
Rather than using ;; outside of the REPL, another idiom is to use let () = ... :

let c = " a string"
let () = print_string (a ^ b ^ c)
2 Likes
6

THANKS. @octachron

I understood it.
XD