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What's New in K5?

oK is an attempt to re-implement K5, a dialect of K which is still in active development, based on released example code, notes and extrapolation from previous versions of K. I am not affiliated with the K5/kOS team and my work is in no way authoritative.

My efforts began with the Reference Manual for K2, the latest complete manual for K I could get my hands on. I then worked from Arthur Whitney's K5 Reference Card and filled in features with some help from the K4/KDB+ information which can be found on the Kx Systems Wiki.

I will attempt to keep this list updated as additional information comes to light or K5 is changed.

Syntax

  • Identifiers can no longer contain underscores. This avoids ambiguity with the drop/cut/floor operator _. May change.

  • Function literals do not supply an argument list, instead relying entirely on the implicit argument names x, y and z. This is reportedly still up in the air. oK supports function argument lists for now.

  • Boolean lists have a special literal syntax. A literal like 011b is a three-element list.

  • The conditional form :[ ... ; ... ; ...] is now $[ ... ; ... ; ...].

  • The imperative constructs do, while and if are gone. do and while can be replaced with some of the forms of / and \, while if is mostly redundant with $[].

Verbs

  • Monadic % is now square root. In K2, this was the reciprocal operator.

  • Monadic ! supplied with a list containing a list of keys and a list of values constructs a dictionary. In K2, this was .. For example:

        !((`a;`b);(1;2))
  [a:1;b:2]

  • Monadic ! supplied with a dictionary will produce a list of keys:

        ![a:1;b:2]
  `a `b

  • Dyadic ^ is the K4 function except. In K2 this was the exponentiation operator.

  • Monadic ^ returns 1 if the right argument is null, otherwise 0. Compare with @. In K2 this was "shape", for determining the number and size of the rectangular dimensions of an array.

Adverbs

Many of the adverbs have overloads when supplied with nouns and no verb as arguments, behaving like an additional set of verbs.

  • ' applied to a left vector and right number performs a binary search in the vector for the number. Right-atomic. Equivalent to the K4 bin builtin.

  • \ applied to a left atom and right list splits the list into sublists at instances of the given atom:

        "&"\"foo=42&bar=69"
  ("foo=42"
   "bar=69")

  • / joins a right list using a left atom. The inverse of split:

        ","/$!5
  "0,1,2,3,4"

  • / applied to a left list of bases and right list is "pack". Used for performing base conversions or in particular converting a collection of bits into an integer. Equivalent to the APL "Decode" operator.

        (8#2)/1000101b
  69
    64 64 64/7 63 63
  32767
    64 64 64/8 0 0
  32768

  • \ applied to a left list of bases and a right number is "unpack". The inverse of "pack".

Intentional Deviations

oK does a few small things differently from other K interpreters by design.

  • oK does not internally discriminate or preserve unitype vectors. As a result, boolean lists are always printed as if they were integers, floating point vectors in which no values have a decimal part will be printed the same as an integer list, etc. This is done purely to simplify the interpreter and may change to be more precisely accurate to K semantics in the future.

  • oK does not preserve the source text of expressions and instead prettyprints based on parsed ASTs which may have been desugared. This aids in debugging and simplifies the interpreter. For example:

        {b[5]+:1}
  {b:.[b;5;+;1]}

  • oK does not support date or time primitive types. This may be added in the future.

  • oK does not provide the same numeric IO verbs as other K interpreters, largely because it is meant as a toy rather than for serious work. Currently 0: is overloaded to write to stdout (dyadic) or read a line at a time as a string from stdin. In the future this functionality might be expanded to support files and ports as in a full K. Another possibility to explore is creating an interface to a subsystem similar to the kOS Z UI system.