Delambda

Delambda is a successor to Unlambda created by User:Shadow Kestrel in 2022. Its syntax and semantics are largely identical to Unlambda, except for the removal of intrinsic functionality from .x functions, removal of the c, e, @, ?x and | functions, and the addition of the o function. This makes the core of Delambda an effectively pure implementation of the SKI combinators with other terms being defineable therein. Additionally, the standard i/o streams are encoded in UTF-8 as opposed to being left unspecified.

The o function

I/O is handled by the o function. If the program evaluates to an expression of the form ``oAB then an action is taken depending on A, then B is applied to the result. For example, ``o`ki`s`ki would read one character from the standard input (corresponding to `ki). Supposing the character read were ě (UTF-8 code c4 9b) then execution would resume as ``s`ki``<cons><church numeral 0xc4>``<cons><church numeral 0x9b><nil>.

Any values taken or given as a "list" are defined with <cons> = ``s``s`ks``s`kk``s`ks``s`k`si``s`kki`k``s`kki; <nil> = `sk

The functionality of ``oAB is as follows:

A	Behaviour
``.x.y.z	Writes "zyx" to stdout
k	Reads the entirety of stdin and returns it as a list of lists (per character, final character deepest) of church numerals (bytewise, LSB deepest). Returns <nil> upon failure.
`ki	Reads a single character from stdin and returns it as a list of church numerals (bytewise, LSB deepest). Returns <nil> upon failure.
`kx	If x is a list of church numerals forming a valid UTF-8 character, returns a .x function for that character. Else, returns v
s	Returns a church numeral, whose binary form denotes the capabilities of the implementation. Any form of `sx or ``sxy is reserved for such functionalities.
Any other term not of the form ``sAB	Error and terminate

Implementation-specific functionality

A Delambda implementation is not required to implement all these functions, as some may not be available in the parent language.

File I/O

Available if `os bit 0 (LSB) is 1. From path ``si.

A	Behaviour
``sii	Reads from a file, prompting user for choice. Returns a list containing the file name (list of bytes, ASCII) and raw data (list of bytes), or <nil> if it fails.
``si`kx	Reads from file x, assuming x is a valid sequence of ASCII .x functions. Returns the raw data of the file as a list of bytes or <nil> if it fails.
``si``sif	Writes the list of bytes f to a file, prompting user for choice. Returns k, or `ki if unsuccessful.
``si`s`kxf	Writes the list of bytes f to file x, assuming x is a valid sequence of ASCII .x functions. Returns k, or `ki if unsuccessful.

Basic Canvas

Available if `os bit 1 is 1. From path ``s`k.

A	Behaviour
``s`kxy	Creates a new canvas of width x and height y, and returns an actionless function corresponding to it.
``s`kCv	Destroys canvas C and returns k or `ki in the event of failure. Note that losing all references to a canvas without destroying it is undefined behaviour and should be avoided.
``s`k``sxy`sCl	Draws pixel (x,y) with colour l on canvas C, returning C. (A colour is a list of three church numerals less than 256 representing RGB)