vim-patch:7.4.2119

Problem:    Closures are not supported.
Solution:   Capture variables in lambdas from the outer scope. (Yasuhiro
            Matsumoto, Ken Takata)

https://github.com/vim/vim/commit/1e96d9bf98f9ab84d5af7f98d6a961d91b17364f

1 files changed, 19 insertions, 1 deletions

diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 62ee26cf54..fb4ca824a3 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -1186,7 +1186,7 @@ the following ways:
 
 1. The body of the lambda expression is an |expr1| and not a sequence of |Ex|
    commands.
-2. The prefix "a:" is optional for arguments.  E.g.: >
+2. The prefix "a:" should not be used for arguments.  E.g.: >
 	:let F = {arg1, arg2 -> arg1 - arg2}
 	:echo F(5, 2)
 <	3
@@ -1195,6 +1195,18 @@ The arguments are optional.  Example: >
 	:let F = {-> 'error function'}
 	:echo F()
 <	error function
+							*closure*
+Lambda expressions can access outer scope variables and arguments.  This is
+often called a closure.  Example where "i" a and "a:arg" are used in a lambda
+while they exists in the function scope.  They remain valid even after the
+function returns: >
+	:function Foo(arg)
+	:  let i = 3
+	:  return {x -> x + i - a:arg}
+	:endfunction
+	:let Bar = Foo(4)
+	:echo Bar(6)
+<	5
 
 Examples for using a lambda expression with |sort()|, |map()| and |filter()|: >
 	:echo map([1, 2, 3], {idx, val -> val + 1})
@@ -1212,6 +1224,12 @@ The lambda expression is also useful for Channel, Job and timer: >
 
 Note how execute() is used to execute an Ex command.  That's ugly though.
 
+
+Lambda expressions have internal names like '<lambda>42'.  If you get an error
+for a lambda expression, you can find what it is with the following command: >
+	:function {'<lambda>42'}
+See also: |numbered-function|
+
 ==============================================================================
 3. Internal variable				*internal-variables* *E461*