2.5. Let expression

There is a short form for match expressions. An expression of the form:
  let letpat = expr1 in expr2
is equivalent to
  match expr1 with letpat => expr2 endmatch
The let expression is, in effect, a prefix operator with the lowest precedence.
Start C++ section to tut/examples/tut208.flx[1 /1 ]
     1: include "std";
     2: print (match 1 with | ?x =>  x + x endmatch); endl;
     3: print (let ?z = 1 in z + z); endl;
     4: print (let ?x = (let ?y = 2 in y + y) in x + x); endl; // 8
     5: 
End C++ section to tut/examples/tut208.flx[1]