3.18. Complier directives
Quirrel has a way to for flexibly customize language features.
This allows to smoothly change compiler, while keeping backward compatibility if needed.
Example
#default:strict
let function foo() {
#relaxed-bool
if (123)
print("bar")
}
Prefix directive with ‘default:’ to apply it to entire VM, otherwise directive applies to clojure in where it is declared.
3.19. List of Complier directives
3.19.1. Strict booleans
#strict-bool
Force booleans in conditional expressions, raise an error on non-boolean types.
Non-boolean in conditional expressions can lead to errors. Because all programming languages with such feature behave differently, for example Python treats empty arrays and strings as false, but JS doesn’t; PHP convert logical expression to Boolean, etc. Another reason is that due to dynamic nature of Quirrel those who read code can’t know what exactly author meant with it.
if (some_var) //somevar can be null, 0, 0.0 or object
or
local foo = a() || b() && c //what author means? What will be foo?
3.19.2. Implicit bool expressions
#relaxed-bool
Original Squirrel 3.1 behavior (treat boolean false, null, 0 and 0.0 as false, all other values as true)
3.19.3. Disable root fallback
#no-root-fallback
Require :: to access root
print(1) //error
::print(1) //prints 1
Implicit root fallback is error prone and a bit slower due to more lookups.
3.19.5. Force explicit access to ‘this’
#explicit-this
Require to explicitly specify ‘this’ or :: to access fields of function environment (‘this’) or root table. This behavior is similar to one in Python. Identifiers must be known local variables, free variables or constants. For unknown names a compilation error is thrown.
3.19.6. Allow implicit access to ‘this’
#implicit-this
Original Squirrel 3.1 behavior. For identifiers not known as local or free variables or constants/enums fallback code performing get/set operations in ‘this’ or root table will be generated.
3.19.7. Disable function declaration sugar
#no-func-decl-sugar
Don’t allow to implicitly add functions to ‘this’ as fields. This also error prone (and functions can be unintentionally added to roottable). Root functions can be added explicitely via slot creation
::foo <- function(){}
Local functions can be added as
let function foo(){}
3.19.8. Allow function declaration sugar
#allow-func-decl-sugar
Allow to implicitly add functions to ‘this’
3.19.9. Disable class declaration sugar
#no-class-decl-sugar
The same directive as #no-func-decl-sugar but for classes. Local classes can be added with:
let class Foo{}
3.19.10. Allow class declaration sugar
#allow-class-decl-sugar
Allow implicitly add classes to ‘this’
3.19.11. Disable access to root table via ::
#forbid-root-table
Forbids use of :: operator for the current unit
Using root table is dangerous (as all global vairables)
3.19.12. Enable access to root table via ::
#allow-root-table
Allows use of :: operator for the current unit
3.19.13. Disable implicit string concatenation
#no-plus-concat
Throws error on string concatenation with +. It is slower for multple strings, use concat or join instead. It is also not safe and can cause errors, as + is supposed to be at least Associative operation, and usually Commutative too. But + for string concatenation is not associative, e.g.
Example:
let a = 1
let b = 2
let c = "3"
(a + b) + c != a + (b + c) // "33" != "123"
This actually happens especially on reduce of arrays and alike.
3.19.14. Enable plus string concatenation
#allow-plus-concat
Allow using plus operator ‘+’ to concatenate strings.