Coding style

Program

• Every function has to be delimited by one empty line.
• Every (non-scoped) function must have a comment directly above it.
• Tests must appear in a single block (no empty lines) one line under the definition.

See the standard library for inspiration.

Function naming

De Bruijn indices can be seen as a disadvantage to readability. It's therefore much more important to name the functions appropriately.

For functions that return a boolean, we suggest using the suffix ?. If your function has different cases it's recommended to use the case- prefix in scoped sub-terms.

# from std/Ternary
zero? [0 case-end case-neg case-pos i] ⧗ Number → Boolean
    case-end true
    case-neg [false]
    case-pos [false]

Appropriate type signatures are also encouraged.

If/else

Since booleans are just lambda terms either returning its first or second argument, the use of if/else procedures is generally redundant. See bit/boolean data structure.

:test (true 'a' 'b') ('a')
:test (false 'a' 'b') ('b')

Head/tail

The internal structure of the list encoding means that when a list is applied to a function, the function is called with the head and tail of the list.

:test ("abc" [[1]]) ('a')
:test ("abc" [[0]]) ("bc")

Therefore the recommended style for coding with lists is to use head/tail only when truly needed.

Recursion

Recursion should almost always be achieved with the y or z combinators.

A common coding style in bruijn's standard library is to use the scoped rec function to indicate recursion. You would then use n+1 abstraction around rec to indicate n arguments and the additionally induced recursive call.

Example of the length function for lists:

# 3 abstractions => two arguments
# 2 is recursive call
# 1 is accumulator (+0)
# 0 is argument (list)
length z [[[rec]]] (+0) ⧗ (List a) → Number
    rec 0 [[[case-inc]]] case-end
        case-inc 5 ++4 1
        case-end 1