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annotate 2-Io/day3-DSL.io @ 46:eac30c1b92da

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Add more notes and try to understand the operators
author IBBoard <dev@ibboard.co.uk>
date Wed, 20 Sep 2017 20:48:37 +0100
parents 8a2451a7b86e
children 409249712590
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1 # Creating a simple "domain-specific language"
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2 # (Except it's not really - it's just a little extension to support
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3 # the "{ key:value[, key:value[…]] }" format of specifying dictionaries)
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4
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5 # Because this is a string then we can do it at any time!
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6 OperatorTable addAssignOperator(":", "atPutThing")
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7
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8 # curlyBrackets is an automatically invoked function from the parser whenever
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9 # it encounters curly brackets.
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10 # This is hidden black magic that you need to know about to override it.
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11 # It appears to call the method for all of the content within the brackets.
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12 curlyBrackets := method(
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13 # Create a map
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14 map := Map clone
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15 # Foreach arg that got passed (each comma-separated line within the brackets)
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16 # then run that on the map
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17 # Note: It isn't clear why ":" operates on the map at this point
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18 # The book says "we'll execute `map atPutThing(a, b)`" but why?
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19 # Colon was originally on a string, not the map, so how does it know to invoke on the map?
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20 call message arguments foreach(arg,
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21 # Based on the following println then it is already "atPutThing(a, b)" by this point
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22 # but the ordering still doesn't make sense.
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23 # See also http://iolanguage.org/guide/guide.html#Syntax-Operators
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24 #
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25 # It *might* be a side-effect of how addAssignOperator works and then the map hijacks
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26 # the values, but that isn't clear from the book OR the documentation!
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27 #arg println
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28 map doMessage(arg)
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29 )
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30 # Return the map (last line's return is the return)
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31 map
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32 )
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33
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34 Map atPutThing := method(
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35 # Call the standard method
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36 self atPut(
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37 # And pull the call args to pass through
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38 # NOTE: arg 1 has its quotes stripped automatically because it's a number
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39 # or some other magic!
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40 call evalArgAt(0) asMutable removePrefix("\"") removeSuffix("\""),
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41 call evalArgAt(1)
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42 )
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43 )
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45 # Note: Trailing commas break things in COMPLETELY CRYPTIC WAYS
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46 # This is because we use doString, which executes it as a program,
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47 # BUT the stack trace doesn't make this clear, so you end up chasing
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48 # bugs in ENTIRELY THE WRONG PART OF THE CODE.
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49 # Eval considered harmful.
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50 the_string := "{
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51 \"foo\": \"12345\",
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52 \"bar\": \"7890\"
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53 }"
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54
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55 phoneNumbers := doString(the_string)
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56 phoneNumbers keys println
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57 phoneNumbers values println
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58
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59 # It feels like implementing something like this should work,
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60 # but it doesn't because "Number does not respond to ':'"
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61 # because we assigned ":" as an assignment operator (like :=)
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62 # and not as a normal operator, although it's then EVEN LESS CLEAR
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63 # how the code in curlyBrackets works
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64 # Also, Io Language docs are poor and don't make it clear how to:
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65 # a) define a range that works; or
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66 # b) do ANYTHING with the OperatorTable
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67 Number atPutThing := method(
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68 call println
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69 return Range (call target) to(call evalArgAt(1))
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70 )
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71
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72 # But presumably this will break, because there's no "atPutThing" method
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73 a := 1
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74 b := 5
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75 range := a : b
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76 # Yep - "Exception: Number does not respond to ':'"
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77 # So you've got to be careful for reusable operators