patch 7.4.2044
Problem: filter() and map() either require a string or defining a function.
Solution: Support lambda, a short way to define a function that evaluates an
expression. (Yasuhiro Matsumoto, Ken Takata)
diff --git a/src/testdir/test_lambda.vim b/src/testdir/test_lambda.vim
new file mode 100644
index 0000000..9e9979b
--- /dev/null
+++ b/src/testdir/test_lambda.vim
@@ -0,0 +1,48 @@
+function! Test_lambda_with_filter()
+ let s:x = 2
+ call assert_equal([2, 3], filter([1, 2, 3], {i, v -> v >= s:x}))
+endfunction
+
+function! Test_lambda_with_map()
+ let s:x = 1
+ call assert_equal([2, 3, 4], map([1, 2, 3], {i, v -> v + s:x}))
+endfunction
+
+function! Test_lambda_with_sort()
+ call assert_equal([1, 2, 3, 4, 7], sort([3,7,2,1,4], {a, b -> a - b}))
+endfunction
+
+function! Test_lambda_with_timer()
+ if !has('timers')
+ return
+ endif
+
+ let s:n = 0
+ let s:timer_id = 0
+ function! s:Foo()
+ "let n = 0
+ let s:timer_id = timer_start(50, {-> execute("let s:n += 1 | echo s:n")}, {"repeat": -1})
+ endfunction
+
+ call s:Foo()
+ sleep 200ms
+ " do not collect lambda
+ call test_garbagecollect_now()
+ let m = s:n
+ sleep 200ms
+ call timer_stop(s:timer_id)
+ call assert_true(m > 1)
+ call assert_true(s:n > m + 1)
+ call assert_true(s:n < 9)
+endfunction
+
+function! Test_lambda_with_partial()
+ let l:Cb = function({... -> ['zero', a:1, a:2, a:3]}, ['one', 'two'])
+ call assert_equal(['zero', 'one', 'two', 'three'], l:Cb('three'))
+endfunction
+
+function Test_lambda_fails()
+ call assert_equal(3, {a, b -> a + b}(1, 2))
+ call assert_fails('echo {a, a -> a + a}(1, 2)', 'E15:')
+ call assert_fails('echo {a, b -> a + b)}(1, 2)', 'E15:')
+endfunc