QUICKREF.md

Flix Quick Reference ↩

This document gathers a few reference informations about the Flix programming language.

Hint: Read the document "Did You Know?" from the Flix documentation to know more about the Flix ecosystem.

Flix language features can be split into two categories :

• features shared with other languages : ADTs and pattern matching, extensible records, type classes, HKTs, type inference, channel and process-based concurrency (like Go).
• unique features : polymorphic effect system, region-based local mutation, purity reflection and first-class Datalog constraints.

Annotations

Flix annotations are defined in file language\ast\Ast.scala :

Definition	Usage examples
@Benchmark	benchmark/BenchmarkConstraint.flix benchmark/BenchmarkList.flix
@Deprecated	unused
@Experimental	library/Benchmark.flix library/Choice.flix
@Internal	library/Debug.flix
@Lazy	library/DelayList.flix library/DelayMap.flix
@LazyWhenPure	library/DelayList.flix library/DelayMap.flix
@MustUse
@Parallel	library/DelayMap.flix
@ParallelWhenPure	library/DelayMap.flix
@Skip	unused
@test	library/TestApplicative.flix library/TestArray.flix

Keywords ▴

The list of Flix keywords is available from several locations :

• Online Flix documentation
• Flix compiler: src\ca\uwaterloo\flix\language\phase\Weeder.scala.

Keyword	Description	Usage examples
alias	Short-hand name for a type. See type	library/File.flix library\Fixpoint\Interpreter.flix
and		library/Array.flix library/Bool.flix library/Eq.flix
as	See import.	library/Console.flix
case	See match.	library/Array.flix
catch	See try.	library/BigInt.flix
class		library/Add.flix
def		library/Add.flix
deref	To access a reference cell.	library/Array.flix
discard		library/Array.flix library/StringBuilder.flix
eff	Only two usages found in Prelude.flix	library/Prelude.flix
else	See if.	library/Array.flix
enum	Flix enumerated types (recurive and polymorphic).	library/Comparison.flix
false		library/Array.flix
fix	Used in Datalog constraints (i.e. in a #{...} block).	library/Graph.flix
forall	Used together with law	library/Applicative.flix
force		library/Bool.flix
foreach		library/List.flix
forM		library/BigInt.flix
from	See select.	library/Graph.flix
if	Flix supports the usual if-then-else expression.	library/Array.flix
import	Interoperability with Java. Usage cases are : Import a Java class/interface (to create objects). Access a Java instance method. Create a Java instance Access a Java static method.	(no usage found in Flix library) library/BigDecimal.flix library/BigDecimal.flix library/BigDecimal.flix
inject		library/Graph.flix
instance		library/Add.flix
into	See inject.	library/Graph.flix
lat	Datalog lattice variable (defined in a #{..} block).	larger-examples/introduction.flix
law		library/Applicative.flix
lawful	Class modifier	library/Applcative.flix
lazy	Lazy evaluation of an expression	library/DelayList.flix
let		library/Array.flix
match		library/Array.flix
mod	Flix modules.	library/Applicative.flix
not		library/Bool.flix
null		library/Files.flix
or
override	See def.	library/List.flix
par	Flix parallelism.	library/DelayMap.flix
pub		library/Array.flix
query		library/Graph.flix
ref		library/Array.flix
region		library/Array.flix
reify
reifyBool
reifyEff
reifyType
rel
resume	Flix effect system (unused in library)
sealed
select	See query.	library/Graph.flix
set
solve		library/Graph.flix
spawn		library/DelayMap.flix
static	See import.	Char.flix
true
try	For interoperability with Java, Flix supports the try-catch mechanism.	library/BigDecimal.flix
type	Unused in library
typematch		library/Array.flix
upcast		library/Prelude.flix
use		library/Channel.flix
where	See select.	library/Graph.flix
with		library/Console.flix
without	Unused in library.
yield	See forM and par.	library/BigInt.flix library/DelayMap.flix

Intrinsic Functions

Intrinsic functions can appear in Flix source code and are translated directly to the underlying JVM operations.

Note: Intrinsic functions are rewritten in method VisitExp in Scala source file ca/uwaterloo/flix/language/phase/Weeder.scala.

Intrinsic function	Usage example
$ARRAY_LENGTHs$	library/Array.flix
$ARRAY_LOAD$	library/Array.flix
$ARRAY_NEW$	library/Array.flix
$ARRAY_STORE$	library/Array.flix
$BOOL_EQ$	library/Eq.flix
$BOOL_NEQ$	library/Eq.flix
...	...

Built-in Functions

The Flix built-in functions are defined in file Flix.scala (value coreLibrary) :

Namespace	Functions
Bool	∨
Boxable
Boxed
Channel	buffered, recv, send, timeout, unbuffered
Comparison
Debug
Eq
Hash
Reflect	default
Sendable
Order
Thread
Time
ToString

Standard Functions ▴

The Flix standard functions are defined in file Flix.scala (value standardLibrary) :

Namespace	Function(s)
Array	head, isEmpty, last, toList, etc.
Assert	eq
Benchmark	runAll, runBenchmark, runBenchmarkOnce, loop
Bigdecimal
BigInt	fromString, min, toString, etc.
Chain
Char	isLetter, isLowerCase, etc.
Choice	Defines the enumeration values Absent and Present.
Console	readLine, print, printLine
Environment	getEnv, getProp, getVar
File	accessTime
Float32
Float64	64-bit float
Int8	8-bit integer
Int16
Int32
Int64	bitCount, factorial, fromString, log2
Iterable	enumerator, iterator
Iterator	isEmpty, next, range, etc.
List	head, isEmpty, toString
StringBuilder	append!, length, toString
Concurrent/Channel
Concurrent/Condition	Condition functions are await, signal, etc.

Predefined Operators

Operator	Description
<-
=>
@
:
:::	The infix operator ::: is an alias for List.append(xs, ys).

Flix Grammar (WIP) ▴

GitHub: src\ca\uwaterloo\flix\language\phase\Parser.scala

Program       = UsesOrImports { Declaration }

UsesOrImports = ( Use | Import ) { Use | Import }

Use           = use ( NQualifiedType '.' NTag
                   | NQualifiedType '.{' { TagAndAlias1 { ',' TagAndAlias1 } } '}'
                   | NNamespace '.' UseName
                   | NNamespace '.{' NameAndAlias1 { ',' NameAndAlias1 } } '}'
                   ) ';'

TagAndAlias1  = NTag [ '=>' NTag ].

NameAndAlias1 = UseName [ '=>' UseName ].

UseName       = NLowerCaseName | NUpperCaseName
              | NGreekName | NMathName | NOperatorName. 

Import      = import NJavaName
              [ '.{' { NameAndAlias { ',' NameAndAlias } } '}' ].

Declaration = Namespace | Def | Law | Enum | RestrictedEnum
            | TypeAlias | Class | Instance | Effect.

Namespace   = mod NNamespace '{' Program '}'.

Def         = Documentation Annotations Modifiers
              def NDefinition TypeParams FormalParamList ':' TypeAndEffect OptTypeConstraintList '=' Stmt.

Sig         = Documentation Annotations Modifiers
              def NDefinition TypeParams FormalParamList ':' TypeAndEfect OptTypeConstraintList [ '=' Stmt ].

Law         = Documentation Annotations Modifiers
              law NDefinition ':'

Enum        = Documentation Annotations Modifiers
              enum NType TypeParams [ TTuple ]
              Derivations Body.

TypeAlias   = Documentation Modifiers
              type alias NType TypeParams '=' Type.

Relation    = Documentation Modifiers
              rel NPredicate TypeParams AttributeList.

Lattice     = Documentation Modifiers
              lat NPredicate TypeParams AttributeList.

Class       = Documentation Annotations Modifiers
              class NClass '[' TypeParam ']'
              [ '{' Law | Sig '}' ].

Instance    = Documentation Modifiers
              instance NQualifiedClass '[' Type ']' OptTypeConstraintList [ '{' { Def } '}' ].

Effect      = Documentation Modifiers
              eff NEffect TypeParams [ '{' { Op } '}' ].

TypeParams  = [ '[' TyeParam { ',' TypeParam } ']' ].

TypeParam   = NVariable [ ':' Kind ].

Compiler Options

GitHub: test\ca\uwaterloo\flix\TestMain.scala

Footnotes ▴

[1] Flix versus Scala ↩

Extract from the Flix FAQ :

Flix looks quite similar to Scala. How are the two languages related?

Flix borrows a lot of syntax from Scala, hence the two languages have a similar feel. We think Scala made many good design choices with respect to syntax, including:
 a) the use of short keywords,
 b) the x : T syntax for type annotations,
 c) the List[Int32] syntax for type parameters, and
 d) if, match, etc. as expressions.

Other than syntax, the two languages are very different:

• Scala is object-oriented, Flix is not.
• Scala has sub-typing, Flix does not.
• The Scala type system is unsound and has imperfect type inference, whereas the Flix type system is both sound and supports type inference.

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mics/May 2024 ▲