Shooting arrows fast and accurately

How to use XQuery arrow expressions for fun and profit.

Transcript

1. Shooting
   Arrows
   fast and accurately
   

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2. Hi!
   I am Juri Leino
   GitHub: @line-o
   twitter: @line_o
   2/55 — XML Prague 2020
   

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3. arrow expressions
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4. arrow expressions
   evaluation order
   A !" f(B, C)
   evaluates to
   f(A, B, C)
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5. arrow expressions
   "hello Prague"
   !" upper-case()
   !" tokenize(" ")
   is the same as
   tokenize(
   upper-case(
   "hello Prague"), " ")
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6. learnings
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7. learnings
   123
   !" function ($a) { $a * $a }
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8. learnings
   123
   !" (function ($a) { $a * $a })()
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9. learnings
   (: 123 "# :)
   (function ($a) { $a * $a })(123)
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10. learnings
    • (1 to 9) !" sum#1
    • error
    • (1 to 9) !" sum(.)
    • error again
    • 'world' !" concat('hello ', ?)
    • anonymous function with arity 1
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11. learnings
    (1, 2, 3) !" count() (: !$ 3 :)
    (1, 2, 3) ! count(.) (: !$ (1, 1, 1) :)
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12. !"!
    A ! B
    A ! B ! C
    A !" B
    A !" B !" C
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13. !"!
    A ! (.) !" B
    A ! f(.) !" B
    (A !" B) ! C
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14. functional
    programming
    a quick recap
    14/55 — Photo by Victor Xok on Unsplash -- XML Prague 2020
    

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15. partial application
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16. partial application
    declare function local:add ($a, $b) { $a + $b };
    let $add16 !" local:add(?, 16)
    let $add48 !" local:add(48, ?)
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17. partial application
    (2, 1, 3, 8)
    ! $add48(.)
    !" codepoints-to-string()
    (: !% "2138" :)
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18. higher order functions
    functions parameterised by or returning a
    function
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19. higher order functions
    • fn:function-arity#1
    • fn:function-name#1
    • fn:function-lookup#2
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20. higher order functions
    • fn:apply#2
    • fn:for-each#2
    • fn:filter#2
    • fn:sort#3
    • fn:fold-left#3
    • fn:fold-right#3
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21. higher order functions
    (2, 1, 3, 8)
    !" for-each($add48)
    !" for-each($add16)
    !" codepoints-to-string()
    (: !% "BACH" :)
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22. Gluten-free
    programming™
    no flour (FLWOR)
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23. Gluten-free programming™
    replace
    for, let, order by, group by, where
    with
    for-each, sort, fold-left, filter
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24. xbow
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25. Like functx, but for
    arrow expressions
    !
    Priscilla Walmsley
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26. (numerical) Comparisons
    gt, ge, lt, le, eq
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27. comparisons
    xbow:gt(5) (: "# function(xs:numeric) :)
    1 "$ xbow:gt(5)() (: "# false() :)
    (1 to 9)
    "$ filter(xbow:gt(5))
    (: "# (6, 7, 8, 9) :)
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28. helpers
    take, last, to-sequence, to-array,
    sortBy, ascending, descending,
    for-each-index, map-reverse,
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29. helpers
    (2, 1, 3, 8)
    !" xbow:descending()
    !" xbow:take(2)
    !" xbow:to-array()
    (: !% [8, 3] :)
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30. helpers
    (6 to 9)
    !" xbow:for-each-index(
    function ($item, $pos) {
    [$pos, $item]
    })
    (: !% ([1, 6], [2, 7], [3, 8], [4, 9]) :)
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31. XML helpers
    wrap-element, wrap-each,
    filter-attributes, attributes-to-map...
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32. reduce
    Boil a sequence down to a boolean
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33. reduce
    (1, 2, 4)
    !" xbow:some(xbow:gt(1)) (: !$ true() :)
    (1, 2, 4)
    !" xbow:all(xbow:le(4)) (: !$ true() :)
    (1, 2, 4)
    !" xbow:none(xbow:gt(10)) (: !$ true() :)
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34. reduce
    (1 to 10)
    !" xbow:group-by(xbow:even-odd(?))
    (: returns :)
    map {
    "even": (2, 4, 6, 8, 10),
    "odd": (1, 3, 5, 7, 9),
    }
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35. accessors
    A function retrieving a value from a (complex)
    item.
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36. accessors
    $posts !" (
    map { "views": 10 },
    map { "views": 1 },
    map { "views": 4922 },
    map { "views": 16 },
    map { "views": 345 }
    )
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37. accessors
    function ($post) { $post?views },
    map:get(?, 'views'),
    xbow:pluck('views')
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38. accessors
    $posts
    !" for-each(xbow:pluck('views'))
    !" filter(xbow:gt(10))
    (: returns :)
    (16, 345, 4922)
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39. accessors
    $posts
    !" for-each(xbow:pluck('views'))
    !" filter(xbow:gt(10))
    !" avg()
    (: returns :)
    1761
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40. accessors
    $posts
    !" filter(
    xbow:gt(10, xbow:pluck('views'))
    (: returns :)
    (
    map { "views": 16 },
    map { "views": 4923 },
    map { "views": 345 }
    )
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41. accessors
    [
    ]
    !# array:filter(
    xbow:gt(2000, function ($y) { xs:integer($y/@n) })
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42. combine
    Merge functions into one
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43. xbow:combine
    $large-sequence
    "# for-each( $a )
    "# for-each( $b )
    "# for-each( $c )
    $large-sequence
    "# for-each(
    xbow:combine(($a, $b, $c)))
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44. categorize
    Clustering data by rules
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45. categorize
    (: A set of rules :)
    let $post-view-rules #$ [
    xbow:eq(0), (: no one :)
    xbow:le(10), (: just a few :)
    xbow:le(100), (: almost successful :)
    xbow:gt(100) (: successful posts :)
    ]
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46. categorize
    (: And a data set :)
    $posts
    "# xbow:categorize(
    $post-view-rules, xbow:pluck('views'))
    (: returns :)
    [
    (),
    (map { "views":"1" }),
    (map { "views":"10" }, map { "views":"16" }),
    (map { "views":"4923" }, map { "views":"345" })
    ]
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47. categorize
    (: we can now label those for human consumption :)
    $posts
    "# xbow:categorize(
    $post-view-rules, xbow:pluck('views'))
    "# xbow:label([
    'no one',
    'just a few',
    'almost successful',
    'successful posts'
    ])
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48. categorize
    (: generate ten complex rules :)
    let $rules "#
    xbow:array-fill(10, function ($item, $ignore) {
    math:pow($item, 4) "% xbow:lt()
    })
    return $posts "% xbow:categorize($rules, xbow:pluck('views'))
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49. Readable Code
    49/55 — XMLPrague 2020 – Photo by Markus Spiske on Unsplash
    

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50. Language
    50/55 — XMLPrague 2020 – Photo by Mark Rasmuson on Unsplash
    

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51. evolution
    51/55 — XMLPrague 2020 – Photo by erokism on Flickr (CC BY 2.0)
    

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52. Take part in it!
    • xquery/XSLT 3.1 (2017)
    • github.com/expath/xpath-ng (2017)
    • xquery/XSLT 4 (?)
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53. Cool things already proposed
    • if without else
    • structure decomposition
    • inline function syntax
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54. What I would like to see
    • the discussion to continue
    • a process to extend and evolve xquery
    • select function by arity and type
    • async, await (over promises)
    • generators
    • tooling (!)
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55. Thanks for having me;
    Go shoot some arrows!
    github.com/line-o/xbow
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