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An odd "non-determinism" example from StackOverflow It is clever, but doesn't make much sense as to how it gets its results
author IBBoard <dev@ibboard.co.uk>
date Sun, 14 Jul 2019 13:44:13 +0100
parents 61dfac9a058a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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17
61dfac9a058a Add some initial experiments with blocks
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1 code-blocks.rb(main):001:0> #! /usr/bin/env ruby
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2 code-blocks.rb(main):002:0*
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3 code-blocks.rb(main):003:0* # Simple passing of code block
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4 code-blocks.rb(main):004:0* 3.times { puts 'Repeated string' }
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5 Repeated string
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6 Repeated string
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7 Repeated string
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8 => 3
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9 code-blocks.rb(main):005:0>
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10 code-blocks.rb(main):006:0* # Extending a class
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11 code-blocks.rb(main):007:0* class Fixnum
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12 code-blocks.rb(main):008:1> def my_times
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13 code-blocks.rb(main):009:2> # We're in a number, so store it as an iterator
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14 code-blocks.rb(main):010:2* i = self
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15 code-blocks.rb(main):011:2> until i == 0
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16 code-blocks.rb(main):012:3> i = i - 1
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17 code-blocks.rb(main):013:3> # Magic happens here!
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18 code-blocks.rb(main):014:3* # Yield normally yields a value, but somehow we're executing a block…
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19 code-blocks.rb(main):015:3* yield
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20 code-blocks.rb(main):016:3> end
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21 code-blocks.rb(main):017:2> end
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22 code-blocks.rb(main):018:1> end
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23 => :my_times
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24 code-blocks.rb(main):019:0>
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25 code-blocks.rb(main):020:0* 3.my_times { puts 'My repeated string' }
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26 My repeated string
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27 My repeated string
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28 My repeated string
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29 => nil
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30 code-blocks.rb(main):021:0>
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31 code-blocks.rb(main):022:0* # Blocks are objects, if you do it right - https://www.ruby-forum.com/topic/49018
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32 code-blocks.rb(main):023:0* my_block = proc { puts 'I am a block' }
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33 => #<Proc:0x000000017361e8@code-blocks.rb:23>
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34 code-blocks.rb(main):024:0> puts my_block.class
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35 Proc
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36 => nil
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37 code-blocks.rb(main):025:0>
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38 code-blocks.rb(main):026:0* # Blocks can be passed around - "&var" says "this is a block"
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39 code-blocks.rb(main):027:0* def call_block(&block)
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40 code-blocks.rb(main):028:1> block.call
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41 code-blocks.rb(main):029:1> end
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42 => :call_block
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43 code-blocks.rb(main):030:0> def pass_block(&block)
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44 code-blocks.rb(main):031:1> call_block(&block)
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45 code-blocks.rb(main):032:1> end
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46 => :pass_block
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47 code-blocks.rb(main):033:0> pass_block { puts 'Inline block' }
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48 Inline block
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49 => nil
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50 code-blocks.rb(main):034:0> pass_block &my_block
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51 I am a block
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52 => nil
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53 code-blocks.rb(main):035:0>
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54 code-blocks.rb(main):036:0* # Without the "&" we get "wrong number of arguments (1 for 0)" because
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55 code-blocks.rb(main):037:0* # a block and an argument are different somehow. This is *not*
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56 code-blocks.rb(main):038:0* # because we were trying to call "my_block" and pass what it returned (nil).
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57 code-blocks.rb(main):039:0* # I tried. Calling a block definitely needs ".call"
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58 code-blocks.rb(main):040:0* #
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59 code-blocks.rb(main):041:0* # This page (https://mixandgo.com/blog/mastering-ruby-blocks-in-less-than-5-minutes)
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60 code-blocks.rb(main):042:0* # makes it cleared: ANY method can take a block independent of its arguments.
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61 code-blocks.rb(main):043:0* # That means that this works:
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62 code-blocks.rb(main):044:0* def pass_var_block(block)
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63 code-blocks.rb(main):045:1> call_block(&block)
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64 code-blocks.rb(main):046:1> end
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65 => :pass_var_block
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66 code-blocks.rb(main):047:0>
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67 code-blocks.rb(main):048:0* pass_var_block my_block
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68 I am a block
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69 => nil
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70 code-blocks.rb(main):049:0>