Fix optarg() and added two more tests.

One for 'do notation' in a single function in an expression, another the trick of using the method call syntax to pass two parameters.

tests/parser/tcommand_as_expr.nim

@@ -1,9 +1,11 @@
 discard """
   output: '''140
-5-120'''
+5-120-120
+359'''
 """
+import math
 
-proc optarg(x:int):int = x
+proc optarg(x:int, y:int = 0):int = x + 3 * y
 proc singlearg(x:int):int = 20*x
 echo optarg 1, singlearg 2
 
@@ -13,5 +15,9 @@ proc foo(x, y: int): int = x-y
 
 let x = optarg foo 7.foo
 let y = singlearg foo(1, foo 8)
+let z = singlearg 1.foo foo 8
     
-echo x, y
+echo x, y, z
+
+let a = [2,4,8].map do (d:int) -> int: d + 1
+echo a[0], a[1], a[2]