Messages

Message are the bread and butter of Gab. They serve many purposes. Mainly they provide control flow, or act as enums or sentinel values. However, They also serve as Gab’s mechanism for polymorphism.

Message Sends

The only way to do anything is by sending a message to a value.

"Hello world!" .println # => Hello world!

Earlier we saw message literals, which look like this:

println:

Now we’ve seen a message send, which is like calling a method or function:

any_value .println

Message literals can also respond to messages!

my_message: .println # => my_message:

In fact, this is how new messages are defined in Gab!

my_message:.def(
    myType,
    () => do
        self.name.println
    end)

Messages themselves respond to the def: message by adding a new implementation for the given type(s). There are several other messages for defining new implementations, which Gab refers to as specializations.

# Define multiple specializations for one message, conveniently
my_message: .defcase {
    nil:  () => "I was nil!"
    true: () => "I was true!"
    none: "I was none!" # Values alone can also serve as a specialization.
}

# Define the same specializations for multiple types, conveniently
[ myType, myOtherType ] .defmodule {
    message_one: () => "Sending message one"
    message_two: () => "Sending message two"
}

Message Values

We’ve seen message values before. They are identifiers that end in a colon:. They’re useful for singleton or sentinel values - and in fact, Gab implements booleans and nil using messages. More on this in later chapters! Gab also uses message values to implement results or optionals. Since Gab has multiple return values, sends that can error often return multiple values like this:

# This call may fail, if Gab can't open the file
(ok file) = IO.file('Maybe_Exists.txt')

(ok file) # => If the file exists  (ok: <gab\box io\file ...>)
          # => If the file doesn't (err: "File not found")

# This line will crash - the record doesn't respond to age:
age = { name: 'bob' } .age

(ok age) = { name: 'bob' }.at(age:)
# Now instead we will either see:
# => (ok: <whatever we saw in the record>)
# => (none: nil:)