implemented optional pragma for implicit discard

1 files changed, 17 insertions, 5 deletions

diff --git a/doc/manual.txt b/doc/manual.txt
index 122668dfb..55a008632 100755
--- a/doc/manual.txt
+++ b/doc/manual.txt
@@ -1474,14 +1474,26 @@ Syntax::
 Example:

 

 .. code-block:: nimrod

+  proc p(x, y: int): int {.optional.} = 
+    return x + y
 

-  discard proc_call("arg1", "arg2") # discard the return value of `proc_call`

+  discard p(3, 4) # discard the return value of `p`

 

 The `discard`:idx: statement evaluates its expression for side-effects and

-throws the expression's resulting value away. If the expression has no

-side-effects, this generates a static error. Ignoring the return value of a

-procedure without using a discard statement is a static error too.

-

+throws the expression's resulting value away. 
+
+Ignoring the return value of a procedure without using a discard statement is
+a static error.
+
+The return value can be ignored implicitely if the called proc/iterator has
+been declared with the `optional`:idx: pragma: 
+
+.. code-block:: nimrod
+  proc p(x, y: int): int {.optional.} = 
+    return x + y
+    
+  p(3, 4) # now valid
+
 

 Var statement

 ~~~~~~~~~~~~~