What

Here's a WIP implementation of the K 2.0 language in OCaml (4.02.3). Some basic things already work. A whole bunch of things does not (yet).

Why

fun, practice etc

How

Kona wiki, K 2.0 reference and manual.

Examples

The Islands example from the Kona wiki (Given a binary matrix, identifies "islands" of 1's and sequentially numbers them):

  grid:(1 0 0 0 1
        1 1 1 0 0
        0 0 0 0 1
        0 0 0 1 1
        1 0 1 1 1
        0 0 1 0 1)
  col:  {x*(^x)#1+!*/^x}                   / give each 1 a unique id
  ab:   {e:{(0,)'x};+(e(+e x))}            / add a border of zeroes
  rb:   {(1_)'1_ x}                        / remove the border of zeroes
  adj:  {(,x),(-1 1!'\:x),(-1 1)!\:x}      / adjacent cells
  mrg:  {(~~x)*|/adj x}                    / merge neighboring ids
  rc:   {.[x;(;);(?0,,/x)?]}               / renumber ids sequentially
  isl:  {rc rb(mrg/col ab x)}              / find islands
  isl grid
(1 0 0 0 2
 1 1 1 0 0
 0 0 0 0 3
 0 0 0 3 3
 4 0 3 3 3
 0 0 3 0 3)

Short examples from Ninety-Nine K problems and K idioms:

  compress:{x@&1,~=':x}
  compress "aaaaabbbccdddeee"
"abcde"
  ? "aaaaabbbccdddeee"  /same result using the range operator
"abcde"
  powerset:{x@&:'!2+&#x}
  powerset (`a;1;"test")
(()
 ,"test"
 ,1
 (1;"test")
 ,`a
 (`a;"test")
 (`a;1)
 (`a;1;"test"))

Loading a CSV file as a column dictionary:

$ cat test.csv
symbols,strings,integers,floats
"abc","def 123",4,5.6
"ghi","ijk 456",7,89.10

$ ./k.native
  table:.{(x;y)}'.("SCIF";,",") 0: "test.csv"
.((`symbols
   `abc `ghi
   )
  (`strings
   ("def 123";"ijk 456")
   )
  (`integers
   4 7
   )
  (`floats
   5.6 89.1
   ))

Build

• Make sure you have OCaml (>=4.02.3) installed. If you are using the opam package manager (recommended), you can check this using opam switch and, if you are using an older version, switch to 4.02.3 using opam switch 4.02.3.
• Build the executable: make k
• (Optionally) run the end-to-end tests: make test-e2e

Current status & notes

Messy, but getting there. ok currently implements just enough to "play around with K". Many features essential to a production system are missing.

The core language is covered almost entirely, while the standard library is quite incomplete.

• Entirely missing: FFI, IPC, networking, date/time ops, attributes, UI.

• Functions can be serialized, but neither their source nor their AST is preserved.

• K-tree namespaces are not faithfully implemented yet. In particular, assignments to the current directory do not have the desired effect (a separate copy is created on writes). As a special-case workaround, the current workspace (entire K-tree) can be saved/loaded to/from disk using the (non-standard) "\load" and "\save" commands:

    $ ./k.native
    ┌──────────┐
    │ok console│
    └──────────┘
      test:123
      \save "my_workspace"
    "my_workspace"
      \\
  
    $ ./k.native
    ┌──────────┐
    │ok console│
    └──────────┘
      \load "my_workspace"
    "my_workspace"
      test
    123
  

• Performance is currently terrible. In particular, Amend always creates a deep copy, even if the structure is only being referenced once.

• Compiler warnings: many partial patterns. Mainly due to infeasible cases omitted for brevity.