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Diffstat (limited to 'runtime/doc/eval.txt')
| -rw-r--r-- | runtime/doc/eval.txt | 57 |
1 files changed, 47 insertions, 10 deletions
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt index cf11b6d77f..b1502f13ca 100644 --- a/runtime/doc/eval.txt +++ b/runtime/doc/eval.txt @@ -112,9 +112,10 @@ You will not get an error if you try to change the type of a variable. 1.2 Function references ~ *Funcref* *E695* *E718* -A Funcref variable is obtained with the |function()| function. It can be used -in an expression in the place of a function name, before the parenthesis -around the arguments, to invoke the function it refers to. Example: > +A Funcref variable is obtained with the |function()| function or created with +the lambda expression |expr-lambda|. It can be used in an expression in the +place of a function name, before the parenthesis around the arguments, to +invoke the function it refers to. Example: > :let Fn = function("MyFunc") :echo Fn() @@ -667,6 +668,7 @@ Expression syntax summary, from least to most significant: @r contents of register 'r' function(expr1, ...) function call func{ti}on(expr1, ...) function call with curly braces + {args -> expr1} lambda expression ".." indicates that the operations in this level can be concatenated. @@ -1174,6 +1176,42 @@ function(expr1, ...) function call See below |functions|. +lambda expression *expr-lambda* *lambda* +----------------- +{args -> expr1} lambda expression + +A lambda expression creates a new unnamed function which returns the result of +evaluating |expr1|. Lambda expressions are differ from |user-functions| in +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.: > + :let F = {arg1, arg2 -> arg1 - arg2} + :echo F(5, 2) +< 3 + +The arguments are optional. Example: > + :let F = {-> 'error function'} + :echo F() +< error function + +Examples for using a lambda expression with |sort()|, |map()| and |filter()|: > + :echo map([1, 2, 3], {idx, val -> val + 1}) +< [2, 3, 4] > + :echo sort([3,7,2,1,4], {a, b -> a - b}) +< [1, 2, 3, 4, 7] + +The lambda expression is also useful for Channel, Job and timer: > + :let timer = timer_start(500, + \ {-> execute("echo 'Handler called'", "")}, + \ {'repeat': 3}) +< Handler called + Handler called + Handler called + +Note how execute() is used to execute an Ex command. That's ugly though. + ============================================================================== 3. Internal variable *internal-variables* *E461* @@ -8094,10 +8132,10 @@ can be 0). "a:000" is set to a |List| that contains these arguments. Note that "a:1" is the same as "a:000[0]". *E742* The a: scope and the variables in it cannot be changed, they are fixed. -However, if a |List| or |Dictionary| is used, you can change their contents. -Thus you can pass a |List| to a function and have the function add an item to -it. If you want to make sure the function cannot change a |List| or -|Dictionary| use |:lockvar|. +However, if a composite type is used, such as |List| or |Dictionary| , you can +change their contents. Thus you can pass a |List| to a function and have the +function add an item to it. If you want to make sure the function cannot +change a |List| or |Dictionary| use |:lockvar|. When not using "...", the number of arguments in a function call must be equal to the number of named arguments. When using "...", the number of arguments @@ -8109,9 +8147,8 @@ until the matching |:endfunction|. It is allowed to define another function inside a function body. *local-variables* -Inside a function variables can be used. These are local variables, which -will disappear when the function returns. Global variables need to be -accessed with "g:". +Inside a function local variables can be used. These will disappear when the +function returns. Global variables need to be accessed with "g:". Example: > :function Table(title, ...) |