Version: v0.7.0 - Beta.  We welcome contributors & feedback.

Format Checker

Programs are meant to be read by humans and only incidentally for computers to execute.

— H. Abelson and G. Sussman
Structure and Interpretation of Computer Programs

Background 

Most programming languages promote a uniform coding style, either with a style guide (e.g. Python’s PEP 8) or with formatting utilities (aka “linters”).

THT goes a step further by having a Format Checker that identifies issues at compile time.

The rules are taken from two main sources:

Benefits of Code Formatting

Q: Why is whitespace so important?

Consistent use of whitespace creates a visual rhythm, and follows our natural ability to visually process information in chunks that are related to each other (see “Gestalt laws of grouping”).

Using conventions frees your brain from the mundane aspects of programming, which offer little payback.

— Steve McConnell, Code Complete

Formatting Rules 

General

Tab Characters

TAB characters are interpreted by THT to be 4 spaces.

We recommend you configure your editor to insert 4 spaces for your Tab key (aka “soft tabs”), if it doesn’t already do so by default.

Whitespace

Indentation

Lines inside multiline braces of {}, [], or () should be indented.

Recommended: 4 spaces

// ✕ No
$notes = [
'Do',
'Re',
'Mi',
]

// ✓ Yes
$notes = [
    'Do',
    'Re',
    'Mi',
]

Infix operators + = == &&

Space before & after: YES

$a = $b + 1  // ✓ Yes
$a = $b+1    // ✕ No
$a=$b+1      // ✕ No

if $isGood && $isOk {...}  // ✓ Yes
if $isGood&&$isOk {...}    // ✕ No

Prefix operators ! -

Spaces after: NO

$isNormal = !$isAdmin   // ✓ Yes
$isNormal = ! $isAdmin  // ✕ No

if !$isAdmin {...}    // ✓ Yes
if ! $isAdmin {...}   // ✕ No

$a = -23   // ✓ Yes
$a = - 23  // ✕ No

Commas ,

Space before: NO
Space after: YES

doSomething($a, $b, $c)  // ✓ Yes
doSomething($a,$b,$c)    // ✕ No

Parentheses ( )

Inside padding: NO
Outer wrapping: NO

doSomething($myVar)    // ✓ Yes
doSomething( $myVar )  // ✕ No

$a = $b / ($c / $d)    // ✓ Yes
$a = $b / ( $c / $d )  // ✕ No

Square braces [ ]

Inside padding: NO

$a = [1, 2, 3]    // ✓ Yes
$a = [ 1, 2, 3 ]  // ✕ No

$user['userId']    // ✓ Yes
$user[ 'userId' ]  // ✕ No

Curly braces { }

Inside padding: YES

$a = { foo: 1 }  // ✓ Yes
$a = {foo: 1}    // ✕ No

if $isOk { return $a }  // ✓ Yes
if $isOk {return $a}    // ✕ No

Colons :

Space before: NO
Space after: YES

$a = { foo: 1 }   // ✓ Yes

$a = { foo : 1 }  // ✕ No
$a = { foo:1 }    // ✕ No

Function argument list ( )

Space before: NO
Space after: YES

fn foo($myVar) {   // ✓ Yes

fn foo($myVar){    // ✕ No
fn foo ($myVar) {  // ✕ No

Open braces {

Space before: YES
Same line: YES
Next line: NO (but allowed)

// ✓ Yes
fn main {
    ...
}

// ✕ No - no space before {
fn main{
    ...
}

// ✕ No - but allowed
fn main
{
    ...
}

Closing braces } ]

Next Line: YES

// ✓ Yes
$nums = [
    111,
    222,
]

// ✕ No
$nums = [
    111,
    222, ]

Trailing comma , after last item

On multiple lines: YES
On single line: NO

// ✓ Yes
$list = [
    111,
    222,
    333,
]      ^

// ✕ No
$list = [1, 2, 3, ]
                ^
// ✓ Yes
$map = {
    aa: 1,
    bb: 2,
    cc: 3,
}        ^

// ✕ No
$map = { aa: 1, bb: 2, cc: 3, }
                            ^

Blank Lines

Use blank lines to group related lines together. Think of consecutive line of code as a “paragraph”.

Rule of Thumb: Avoid having 4 or more consecutive lines of code (not counting lone braces).

// ✕ No

$userName = getUserName()
if $userName == 'admin': return true
$userAgeDays = getUserAgeDays($userName)
if $userAgeDays > 1000: return true


// ✓ Yes

$userName = getUserName()
if $userName == 'admin': return true

$userAgeDays = getUserAgeDays($userName)
if $userAgeDays > 1000: return true

Parser Rules 

Assignment inside conditional: NO

// ✕ No
if $line = readLine() {...}

// ✓ Yes
$line = readLine()
if $line {...}

Nested ternary expressions: NO

// ✕ No
check1 ? action1() : check2 ? action2() : action3()

// ✓ Yes - if/else
$a = ''
if check1 {
    $a = action1()
}
else if check2 {
    $a = action2()
}
else {
    $a = action3()
}

// ✓ Yes - 'match' with one-liner syntax
$a = ''
match {
    check1:   $a = action1()
    check2:   $a = action2()
    default:  $a = action3()
}

Max function arguments: 4

// ✕ No - More than 4 arguments
fn doSomething($a1, $a2, $a3, $a4, $a5) {
    ...
}

// ✓ Yes - Combine args into a Map, etc.
doSomething('foo', {
    flag: true,
    num: 123,
})

fn doSomething($mainArg, $otherArgs) {
    if $otherArgs['flag'] {
        ...
    }
}

// ✓ Yes - Split into smaller functions
fn doSomething($a1, $a2) {
    ...
}

fn doOtherThing($a3, $a4, $a5) {
    ...
}

Names

Module and class names are strict UpperCamelCase. This includes acronyms.

User
XmlReader
XmlHttpRequest

All other names (variables, functions, bare map keys) are strict camelCase. This includes acronyms.

user
firstName
userId
userHasIphone
httpOutput

HTML Templates 

These are additional rules for markup within HTML Template Functions.

Tag Names

Uppercase: NO

// ✕ No
<SPAN>

// ✓ Yes
<span>

Parameters

Quoted: YES

// ✕ No
<div class=my-class>

// ✓ Yes
<div class="my-class">

Space around equals: NO

// ✕ No
<div class = "my-class">

// ✓ Yes
<div class="my-class">