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Design Spikes
Hillclimbing Design Spike



NOTE: This software was written for the Swift 1.0 beta release; it needs to be updated for modern Swift releases.

A Mac desktop genetic programming system using a simple interpreted language based closely on the PushGP system for genetic programming (work by Lee Spector, Maarten Keijzer, Jon Klein, Chris Perry and Tom Helmuth, among others).

With several amendments.


To learn some TDD habits in XCode, and explore Apple's new Swift language.


  • 6 June 2014: Just barely started.

  • 14 June 2014: Push interpreter built, most trivial instructions running and tested. No I/O or UI at all, so it only runs in XCode under test. About to start building an Answer class, which will be the genetic programming "individuals".

  • 20 June 2014: Most of Push 3 instructions and Range type are done; considering how to handle arithmetic overflow

  • 7 February 2015: Finally rolled up my sleeves and repaired a whole slew of compile errors that arose when Swift 1.x was released: these involved access control (which didn't exist when I started), various new bridges to Objective C (ditto), loads of syntax quirks and minor changes (like the .. operator is now the ... operator), and so on. Also deleted many little dumb stubs that arose in the process of working with XCode 6 beta before Yosemite was available to me.

    Tabula rasa for setting up an actual search process, and building this out as a library proper.


  • Push 3.0 types baked in: Int, Bool, Float (Double, in this case), Code, Name
  • Off-label syntax: Unlike Push 3.0, the ( and ) tokens here are independent; the parser reads scripts left-to-right, and opens a new block when it encounters a (, closing as with normal syntax rules. But extra ) encountered are ignored, and missing ) after the script is fully parsed implicitly causes all open blocks to be closed immediately.
  • Off-label Tozier-flavored types built in: Range, representing an oriented contiguous block of integers. Probably will also add the Proportion type (representing values confined to [0,1] and acting like probabilities), Span (representing segments of real number line, with Doubles as start and ending values and also oriented).
  • Off-label instructions:
    • anything having to do with Ranges
    • some minor changes and improvements to inter-type conversion methods (notably bool_from* methods use the sgn(x) to determine the value of the resulting Bool, not whether it's 0 or 1
    • some changes and extensions to code-manipulation methods (more shortly)
    • exec_map and code_map instructions, which execute code over entire stacks full of arguments
    • more stack manipulation instructions, including *_flip (which reverses a stack), *_double (which clones the entire stack onto itself) and *_archive which pushes an item onto the bottom of the exec stack
    • some interpreter state variations, like push_nopop which leaves arguments on the origin stacks


  • build a parser that converts Push [dialect] scripts into code points
  • build an interpreter that executes [most of] the instructions defined in the Push 3.0 Specification and Clojush
  • add a few simple extensions to the basic type structure from our GPTP conferences through the years
    • tag spaces?
    • Range types
    • Set and/or collection types
    • implied block structure
  • build a simple desktop [?] app that loads training and test data, and runs interactively to produce data logs and results in realtime
  • let the app solve problems locally using modern Pareto-GP approaches, lexicase selection, and so on
  • maybe some cloud things; you know, for kids