number_in_month exercise

Question

I am fresh on SML and doing a homework by that. \"Write a function number_in_month that takes a list of dates and a month (i.e., an int) and returns how many dates in the li

Answer 1

The error message from REPL is confusing, but Jesper is right that you should use let-in-end expression, if you need assignment statement in functions. That will surely get you that error resolved.