In Erlang, the equivalent of a let fails.
1> 1=2.
** exception error: no match of right hand side value 2

In SML, the equivalent of a let fails.
- val 1 = 1;
- val 1 = 2;

uncaught exception Bind [nonexhaustive binding failure]
  raised at: stdIn:2.5-2.10

The problem is not that let 1 = 2 ... is *legal* but that
- the compiler is  *silent* about it
- the runtime is *silent* about it.
Compiling the little program

  main = let 1 = 2 in print "hi"

I expected that the compiler would be silent but that
there would be some sort of "matched failed" error at
run time.  Silly me.


The thing is, it is not just bindings that bind no variables
that act as if they were not there.

  main = let [x] = [1,2] in print "hi"

also compiles silently and runs without error.  Change it to

  main = let [x] = [1,2] in print ("hi" ++ show x)

and you get a runtime error

<object>: <source>: Irrefutable pattern failed for pattern [x].

I wish the compiler would report an error something like

"<location>: possibly failing match deleted
             because it binds no live variables"