mirror of
https://github.com/carbon-language/carbon-lang.git
synced 2026-10-04 22:02:52 +01:00
Jon Meow
79a9b51d07
Adopts new copyright and markdown toc checks. The new toc check generates the toc header, so that's why all the md files changed (this had felt better to me for the long-term, more auto-generated content)
81 lines
2.4 KiB
Markdown
81 lines
2.4 KiB
Markdown
# Control flow
|
|
|
|
<!--
|
|
Part of the Carbon Language project, under the Apache License v2.0 with LLVM
|
|
Exceptions. See /LICENSE for license information.
|
|
SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
-->
|
|
|
|
<!-- toc -->
|
|
|
|
## Table of contents
|
|
|
|
- [TODO](#todo)
|
|
- [Overview](#overview)
|
|
- [Open questions](#open-questions)
|
|
- [`if` blocks](#if-blocks)
|
|
- [`break` and `continue`](#break-and-continue)
|
|
|
|
<!-- tocstop -->
|
|
|
|
## TODO
|
|
|
|
This is a skeletal design, added to support [the overview](README.md). It should
|
|
not be treated as accepted by the core team; rather, it is a placeholder until
|
|
we have more time to examine this detail. Please feel welcome to rewrite and
|
|
update as appropriate.
|
|
|
|
At least summarize `if` and `else` to cover basics. Especially important to
|
|
surface the idea of using basic conditionals as both expressions and statements
|
|
to avoid needing conditional operators.
|
|
|
|
Looping is an especially interesting topic to explore as there are lots of
|
|
challenges posed by the C++ loop structure. Even C++ itself has been seeing
|
|
significant interest and pressure to improve its looping facilities.
|
|
|
|
## Overview
|
|
|
|
Blocks of statements are generally executed linearly. However, statements are
|
|
the primary place where this flow of execution can be controlled. Carbon's
|
|
control flow constructs are mostly similar to those in C, C++, and other
|
|
languages.
|
|
|
|
```
|
|
fn Foo(Int: x) {
|
|
if (x < 42) {
|
|
Bar();
|
|
} else if (x > 77) {
|
|
Baz();
|
|
}
|
|
}
|
|
```
|
|
|
|
Loops will at least be supported with a low-level primitive `while` statement,
|
|
with `break` and `continue` statements which work the same as in C++.
|
|
|
|
Last but not least, for the basics we need to include the `return` statement.
|
|
This statement ends the flow of execution within a function, returning it to the
|
|
caller. If the function returns a value to the caller, that value is provided by
|
|
an expression in the return statement. This allows us to complete the definition
|
|
of our `Sum` function from earlier as:
|
|
|
|
```
|
|
fn Sum(Int: a, Int: b) -> Int {
|
|
return a + b;
|
|
}
|
|
```
|
|
|
|
## Open questions
|
|
|
|
### `if` blocks
|
|
|
|
It is an open question whether a block is required or a single statement may be
|
|
nested in an `if` statement. Similarly, it is an open question whether `else if`
|
|
is a single keyword versus a nested `if` statement, and if it is a single
|
|
construct whether it should be spelled `elif` or something else.
|
|
|
|
### `break` and `continue`
|
|
|
|
If and how to support a "labeled break" or "labeled continue" is still a point
|
|
of open discussion.
|