Rant implements anonymous (nameless) functions as lambda expressions, commonly referred to as simply lambdas. The body of a lambda can also capture variables from its environment, just like regular named functions.

Basic lambda expression syntax with no parameters consists of a ? symbol inside brackets preceding the function body.

# Creates a function and places it on the output
[?] { Hello from lambda expression! }


If your lambda body contains a block at the root level, you will need to enclose it in another block to differentiate it from a function body block.


# Compiler error
[?] { foo | bar }

# Correct syntax
[?] {{ foo | bar }}


If you want to add parameters to a lambda, just specify the parameters after the colon as you would with a normal function definition:

[?: param1; param2] { ... }

Calling an anonymous function

Since lambdas produce function objects just like named functions, the call syntax is very similar. Simple use an anonymous access path to supply the function in the call.

# Define a function that returns a parameterless function
[$get-anon-func] {
    [?]{Hello from anonymous function}

[([get-anon-func])]         # -> "Hello from anonymous function"

# Define a function that returns a function with a single parameter
[$get-greet-func] {
    [?:name]{Hello, <name>!}

[([get-greet-func]): Rant]  # "Hello, Rant!"

Using piping to call an anonymous function produced by another function

The above example could be simplified with piping: just call [get-anon-func], then call [] directly.

[get-anon-func |> []: ## args... ##]