juvix/CODING.md

Juvix coding style guidelines for the standard library and Anoma apps

Definitions

• enumeration type is an inductive type whose all constructors have zero arguments

General rules

• always use the formatter
• don't use unicode, except perhaps for judoc
• avoid Pair
• prefer enumeration types with meaningful constructor names over booleans, e.g., instead of using Bool define:

type Transferability :=
  | Transferable
  | NonTransferable;

Imports

• all imports at the beginning of the file
• explicit names for imported identifiers (import X open using {iden1; iden2})
  • exception: import Stdlib.Prelude open and import Anoma open are allowed

Names

• types: upper camel case (Nat, PublicKey)
• functions, constructors, etc: lower camel case (tokenLogic, transferLogic)
  • exception: constructors of enumeration types: upper camel case

type BalanceFactor :=
  | --- Left child is higher.
    LeanLeft
  | --- Equal heights of children.
    LeanNone
  | --- Right child is higher.
    LeanRight;

type Ordering :=
  | LessThan
  | Equal
  | GreaterThan;

• instances: lower camel case with I at the end: trait + type + I, e.g., instance eqNatI : Eq Nat := ..
• boolean check functions: start with is (isWhatever)
• record constructors: mk + type name (mkResource)
• meaningful descriptive long names for arguments of public functions, e.g., element, list, initialValue
  • exception: common abbreviations allowed: fun, acc, elem
  • exception: generic functions whose arguments have no specific meaning, e.g.,

id {A} (x : A) : A := x

• short names like x are okay for local definitions

Function signatures

• put everything to the left of : in type signatures, with full meaningful names for arguments
  • temporary exception: when needed for termination, argument can be moved to the right of :
  • even when the argument type is moved to the right, give a descriptive argument name in the type:

isMember {A} (testEq : A -> A -> Bool) (element : A) : (list : List A) -> Bool

Type variables

• type variables uppercase (upper camel case, like with types)
• higher-order type variables also upper camel case (F : Type -> Type)
• implicit type variables: use short version {A} in function signatures on the left
• prefer {A B} over {A} {B} in function signatures
• meaningful type variable names for more "high-level" functions where this makes sense

Example:

split
  {ResourceType}
  {{Convertable ResourceType}}
  {{HasOwner ResourceType}}
  {{HasQuantity ResourceType}}
  {{HasTransferability ResourceType}}
  {{TransactionConvertable ResourceType ResourceType}}
  (self : KeyPair)
  (toSplit : ResourceType)
  (quantitiesAndReceivers : List (Pair Nat PublicKey))
  : Result StandardError Transaction :=
  ...

But we can use a short name A in:

find {A} (predicate : A -> Bool) : (list : List A) -> Maybe A

Pattern matching

• use case whenever possible; matching on multiple values handled with pairs
• don't use pattern matching with side conditions when there is an else side condition -- convert to an if in the body instead
• don't pattern match on Bool -- use if instead

Application

• don't use "pipes" (i.e., |>, <|, >>, <<, etc.)
  • exception: there is a "natural" data processing pipeline in several steps, e.g.,

map (+ 1) >> filter (< 0) >> sum

• use iterators for , map, etc., instead of the function application syntax with fold, etc.
• use named application when reasonable

Type definitions

• use ADT syntax
• every constructor on a separate line
• give meaningful names to constructor arguments

Example:

type BinaryTree (A : Type) :=
  | leaf
  | node@{
      left : BinaryTree A;
      element : A;
      right : BinaryTree A
    };

Documentation

• the documentation string should be an English sentence
• mention the meaningful argument names in the function's judoc