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<!DOCTYPE html>
	<html class="sl-root decks export offline loaded">
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		<title>chrysanthemum</title>


		<link rel="stylesheet" type="text/css" href="lib/offline-v2.css">



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		<div class="reveal">
			<div class="slides">
				<section data-id="a4661b2bbd4624c846921874ba673364"><div class="sl-block" data-block-type="text" style="width: 806px; left: 78px; top: 238px; height: auto;" data-block-id="791c2b40c03699f6fde69d16c2186a3f"><div class="sl-block-content" data-placeholder-tag="h1" data-placeholder-text="Title Text" style="z-index: 10;">
<h1><s>typeclasses</s></h1>

<p><s>also</s> bidirectional typechecking and subtyping</p>
</div></div>
<div class="sl-block" data-block-type="text" style="height: auto; width: 600px; left: 180px; top: 509.5px;" data-name="text-2840e2" data-block-id="67d13465aa6485a5c990f43539cf415f"><div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Text" style="z-index: 11;"><p>ten slides, five minutes</p></div></div></section><section data-id="b3131b7538da110564ed88c19f88f798"><div class="sl-block" data-block-type="text" style="width: 420px; left: 29px; top: 84px; height: auto;" data-block-id="ae6fb9a98dfec970cd7c79e600eb5fe8"><div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="text-align: left; z-index: 11;"><h3>the lambda calculus</h3></div></div>
<div class="sl-block" data-block-type="text" style="width: 428px; left: 29px; top: 175px; height: auto;" data-block-id="7838a236af12095f9c2f16dcf852100a"><div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi nec metus justo. Aliquam erat volutpat." style="z-index: 13; text-align: left; line-height: 1.625;" data-has-line-height=""><ul>
	<li><span style="font-size:0.9em">no time, others also did this</span></li>
	<li><span style="font-size:0.9em">rust good bottom text</span></li>
	<li><span style="font-size:27px">algebraic data types &lt;&lt;3</span></li>
	<li><span style="font-size:0.9em">bidirectional typechecking</span></li>
	<li><span style="font-size:0.9em"><strong>infer</strong>, <strong>check</strong>, <strong>execute</strong></span></li>
	<li><span style="font-size:0.9em">bounce back and forth between infer and check</span></li>
	<li><span style="font-size:0.9em">scaling, first class functions:   a problem for the future</span></li>
</ul></div></div>
<div class="sl-block" data-block-type="code" style="width: 451px; height: 630px; left: 480px; top: 35px;" data-name="code-78376e" data-block-id="0241b4282f3a776e15a9e530e6d4d173"><div class="sl-block-content notranslate" data-highlight-theme="ascetic" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;" data-code-wrap="true"><pre class="ocaml" style="font-size: 14px; line-height: 17px;"><code data-line-numbers="">pub type Value = u8;

pub struct Term {
  pub val: Value,
  pub kind: Type, // for casting
}

pub type Identifier = String;
pub type Context = HashMap&lt;Identifier, Term&gt;;

#[derive(Clone, PartialEq, Eq)]
pub enum Expression {
  Annotation {
    expr: Box&lt;Expression&gt;, 
    kind: Type
  },
  Constant {
    term: Term
  },
  Variable {
    id: Identifier
  },
  Abstraction {
    param: Identifier, 
    func: Box&lt;Expression&gt;
  },
  Application {
    func: Box&lt;Expression&gt;, 
    arg: Box&lt;Expression&gt;
  },
  Conditional {
    if_cond: Box&lt;Expression&gt;, 
    if_then: Box&lt;Expression&gt;, 
    if_else: Box&lt;Expression&gt;
  }
}
</code></pre></div></div></section><section class="stack" data-id="415287af0ae5feeb1d12a5d12ae5bdee"><section data-id="3d62bb80cc8ceab908cb8c9e8e38e89d"><div class="sl-block" data-block-type="text" style="width: 400px; left: 520px; top: 367px; height: auto;" data-block-id="7c5a36cb564fd5c7b314f0fe46b96e18"><div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="z-index: 11; text-align: center; background-color: rgb(255, 255, 255); border-style: solid; border-width: 1px; padding: 10px; --darkreader-inline-bgcolor:#181a1b;" data-darkreader-inline-bgcolor="">
<h2>parsing</h2>

<p>pegs are magic</p>

<p>very nice for simple stuff</p>
</div></div>

<div class="sl-block" data-block-type="code" style="width: 960px; height: 700px; left: 0px; top: 0px;" data-name="code-18c030" data-block-id="fbbb08031772ba21433337c8b6216bbd"><div class="sl-block-content notranslate" data-highlight-theme="xcode" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;" data-code-wrap="true"><pre class="rust" style="font-size: 16px; line-height: 19px;"><code data-line-numbers="">/// Parses a lambda-calculus-like language into an AST.
pub fn parse_str(input: &amp;str) -&gt; Result&lt;Expression, peg::error::ParseError&lt;peg::str::LineCol&gt;&gt;{
    // this is kinda gross
    // i miss my nim pegs
    peg::parser!{
        grammar lambda() for str {
            rule identifier() -&gt; String
            = i:['a'..='z' | 'A'..='Z' | '0'..='9']+ {
                i.iter().collect::&lt;String&gt;()
            }
            rule constant() -&gt; Expression
            = p:"-"? c:['0'..='9']+ {
                let value = c.iter().collect::&lt;String&gt;().parse::&lt;Value&gt;().unwrap();
                Expression::Constant {
                    term: Term {
                        val: if let Some(_) = p {
                            value.wrapping_neg()
                        } else {
                            value
                        },
                        kind: Type::Empty
                    }
                }
            }
            rule primitive() -&gt; Type
            = k:$("empty" / "unit" / "bool" / "nat" / "int") {
                match k {
                    "empty" =&gt; Type::Empty,
                    "unit" =&gt; Type::Unit,
                    "bool" =&gt; Type::Boolean,
                    "nat" =&gt; Type::Natural,
                    "int" =&gt; Type::Integer,
                    _ =&gt; Type::Empty
                }
            }
            rule function() -&gt; Type = "(" f:kind() " "* "-&gt;" " "* t:kind() ")" {
                Type::Function { from: Box::new(f), to: Box::new(t) }
            }
            rule kind() -&gt; Type
             = k:(function() / primitive()) {
                k
            }
            rule annotation() -&gt; Expression
            = e:(conditional() / abstraction() / application() / constant() / variable()) " "* ":" " "* k:kind() {
                Expression::Annotation {
                    expr: Box::new(e),
                    kind: k
                }
            }
            rule variable() -&gt; Expression
            = v:identifier() {
                Expression::Variable {
                    id: v
                }
            }
            rule abstraction() -&gt; Expression
            = ("λ" / "lambda") " "* p:identifier() " "* "." " "* f:expression() {
                Expression::Abstraction {
                    param: p,
                    func: Box::new(f)
                }
            }
            rule application() -&gt; Expression
            = "(" f:(annotation() / abstraction()) ")" " "* a:expression() {
                Expression::Application {
                    func: Box::new(f),
                    arg: Box::new(a)
                }
            }
            rule conditional() -&gt; Expression
            = "if" " "+ c:expression() " "+ "then" " "+ t:expression() " "+ "else" " "+ e:expression() {
                Expression::Conditional {
                    if_cond: Box::new(c),
                    if_then: Box::new(t),
                    if_else: Box::new(e)
                }
            }
            pub rule expression() -&gt; Expression
            = e:(conditional() / annotation() / abstraction() / application() / constant() / variable()) {
                e
            }
            pub rule ast() -&gt; Vec&lt;Expression&gt;
            = expression() ** ("\n"+)
        }
    }
    return lambda::expression(input.trim());
}</code></pre></div></div></section><section data-id="b571280a25332e373ef4c198d796bf9e"><div class="sl-block" data-block-type="text" style="width: 400px; left: 520px; top: 396px; height: auto;" data-block-id="4304ebe755544fa0129f72a9b727e2eb"><div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="z-index: 11; text-align: center; background-color: rgb(255, 255, 255); border-style: solid; border-width: 1px; padding: 10px; --darkreader-inline-bgcolor:#181a1b;" data-darkreader-inline-bgcolor="">
<h2>oh god</h2>
<p>why did i decide to do this<br></p>
</div></div>

<div class="sl-block" data-block-type="code" style="width: 960px; height: 700px; left: 0px; top: 0px;" data-name="code-18c030" data-block-id="a053327817730688c30270bd7790eaec"><div class="sl-block-content notranslate" data-highlight-theme="xcode" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;" data-code-wrap="true"><pre class="rust" style="font-size: 16px; line-height: 19px;"><code data-line-numbers="">/// Parses a simple language with bracket-based indentation and end-of-term semicolons.
#[allow(unused_variables)]
pub fn parse_lang(input: &amp;str) -&gt; Result&lt;Vec&lt;Expression&gt;, peg::error::ParseError&lt;peg::str::LineCol&gt;&gt; {
  peg::parser! {
    grammar puck() for str {
      // whitespace
      rule w() = ("\n" / " ")+
      // todo: multiple parameters pls
      rule abs() -&gt; Expression
      = "func" w() n:ident() w()? "(" p:ident() ")"
        w()? ":" w()? k:function() w() "=" w() "{" w() f:expr() w() "}" {
        Expression::Annotation {
          expr: Box::new(Expression::Abstraction { param: p, func: Box::new(f) }),
          kind: k
        }
      }
      // fixme: this requires, uh, refactoring the ast...
      rule app() -&gt; Expression
      = f:ident() "(" a:expr() ")" {
        Expression::Application {
          func: Box::new(Expression::Variable { 
            id: f 
          }),
          arg: Box::new(a)
        }
      }
      rule cond() -&gt; Expression
      = "if" w() c:expr() w() "=" w() "{" w() t:expr() w() "};" w() 
        "else" w() "=" w() "{" w() e:expr() w() "}" {
        Expression::Conditional {
          if_cond: Box::new(c),
          if_then: Box::new(t),
          if_else: Box::new(e)
        }
      }
      // fixme: cannot say e:(expr()), left-recursion issue
      rule ann() -&gt; Expression
      = e:(cond() / abs() / app() / cons() / var()) w()? ":" w() k:kind() {
        Expression::Annotation {
          expr: Box::new(e),
          kind: k
        }
      }
      // identifiers
      rule ident() -&gt; String = i:['a'..='z' | 'A'..='Z' | '0'..='9']+ {
        i.iter().collect::&lt;String&gt;()
      }
      rule var() -&gt; Expression
      = v:ident() {
        Expression::Variable {
          id: v
        }
      }
      // constants
      rule cons() -&gt; Expression = p:"-"? c:['0'..='9']+ {
        let value = c.iter().collect::&lt;String&gt;().parse::&lt;Value&gt;().unwrap();
        Expression::Constant {
          term: Term {
            val: if let Some(_) = p {
              value.wrapping_neg()
            } else {
              value
            },
            kind: Type::Empty // fixme
          }
        }
      }
      // types
      rule primitive() -&gt; Type = k:$("empty" / "unit" / "bool" / "nat" / "int") {
        match k {
          "empty" =&gt; Type::Empty,
          "unit" =&gt; Type::Unit,
          "bool" =&gt; Type::Boolean,
          "nat" =&gt; Type::Natural,
          "int" =&gt; Type::Integer,
          _ =&gt; Type::Empty // never happens
        }
      }
      // fixme: parenthesis necessary, left-recursion issue
      rule function() -&gt; Type = "(" w()? f:kind() w()? "-&gt;" w()? t:kind() w()? ")" {
        Type::Function { from: Box::new(f), to: Box::new(t) }
      }
      // todo: records, etc
      rule kind() -&gt; Type
       = k:(function() / primitive()) {
        k
      }
      pub rule expr() -&gt; Expression
      = e:(ann() / cond() / abs() / app() / cons() / var()) ";" {
        e
      }
      pub rule file() -&gt; Vec&lt;Expression&gt;
      = expr() ++ "\n"
    }
  }
  return puck::file(input);
}
</code></pre></div></div></section><section data-id="5b7407362576e3330ce5a041db94c4f6"><div class="sl-block" data-block-type="code" style="width: 372px; height: 315px; left: 28px; top: 350px;" data-name="code-fec34b" data-block-id="0465bb1bf164ad420888c724cd3d6956">
    <div class="sl-block-content notranslate" data-highlight-theme="ascetic" data-code-frame="none" style="z-index: 11; border-style: solid; border-width: 1px;" data-code-wrap="true">
        <pre class="nim" style="font-size: 16px; line-height: 19px;"><code data-line-numbers="">func negate(x): (bool -&gt; bool) =
  if x: 0
  else: 1

func fib(x): (int -&gt; int) =
  if eq(x, 0):
    0
  else:
    if eq(x, 1):
      1
    else:       # comment
      add(fib(sub(x, 1)), 
          fib(sub(x, 2)))

negate(negate(1))
fib(5)
</code></pre>
    </div>
</div>
<div class="sl-block" data-block-type="code" style="width: 511px; height: 630px; left: 434.5px; top: 35px;" data-block-id="6a738ee3f5ae23601928ee4c798bf6f2" data-name="code-729f31">
    <div class="sl-block-content notranslate" data-highlight-theme="ascetic" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;" data-code-wrap="true">
        <pre class="none" style="font-size: 16px; line-height: 19px;"><code data-line-numbers="">/// Converts a whitespace-indented language 
/// into a bracketed language for PEG matching.
pub fn lex(input: &amp;str) -&gt; 
    Result&lt;String, &amp;'static str&gt; {
  #[derive(Eq, PartialEq)]
  enum Previous {
    Start,
    Block,
    Line,
  }
  struct State {
    blank: bool, // entirely whitespace so far?
    level: usize, // current indentation level
    count: usize, // current whitespace count
    previous: Previous,
    comment: bool // current line a comment?
  }
  let indent_size: usize = 2;

  let mut state = State { 
    blank: true, 
    level: 0, 
    count: 0, 
    previous: Previous::Start, 
    comment: false 
  };
  let mut buffer = String::new();
  let mut result = String::new();

  // wow lexers are hard
  for c in input.chars() {
    match c {
      '\n' =&gt; {
      if !buffer.is_empty() {
        if state.count == state.level {
          if state.previous != 
            Previous::Start {
            result.push(';');
            result.push('\n');
          }
          state.previous = Previous::Line;
        } else if state.level + indent_size
               == state.count {
          result.push(' ');
          result.push('{');
          result.push('\n');
          state.level = state.count;
          state.previous = Previous::Line;
        } else if state.count &gt; 
                  state.level + indent_size {
          return Err("invalid indent jump");
        } else if state.count % indent_size 
                                       != 0 {
          return Err("incorrect indent offset");
        } else if state.level &gt; state.count {
          while state.level &gt; state.count {
            if state.previous == 
               Previous::Line {
              result.push(';');
            }
            state.level -= indent_size;
            result.push('\n');
            result.push_str(
                   &amp;" ".repeat(state.level));
            result.push('}');
            result.push(';');
            state.previous = Previous::Block;
          }
          result.push('\n');
        } else {
          return Err("unknown indentation");
        }

        result.push_str(
               &amp;" ".repeat(state.count));
        result.push_str(&amp;buffer);

        state.count = 0;
        state.comment = false;
        buffer.clear();
        }
        state.blank = true;
      },
      ' ' if state.blank =&gt; {
        state.count += 1;
      },
      '#' =&gt; {
        state.blank = false;
        state.comment = true;
      },
      _ =&gt; {
        if state.blank {
          state.blank = false;
        }
        if !state.comment {
          buffer.push(c);
        }
      },
    }
  }
  if state.previous == Previous::Line {
    result.push(';');
  }
  while state.level != 0 {
    state.level -= 2;
    result.push('\n');
    result.push_str(&amp;" ".repeat(state.level));
    result.push('}');
    result.push(';');
  }
  return Ok(result);
}</code></pre>
    </div>
</div>
<div class="sl-block" data-block-type="text" style="width: 384px; left: 28px; top: 106px; height: auto;" data-block-id="91eb6fbcf652855c2504b2ff23e1e2ce" data-name="text-a739f8">
    <div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="text-align: left; z-index: 12;"><h3>don't write a parser</h3></div>
</div>
<div class="sl-block" data-block-type="text" style="width: 384px; left: 28px; top: 202px; height: auto;" data-block-id="b0c9d472583c05a21d1f5ee7082ba525" data-name="text-64290a">
    <div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Proin urna odio, aliquam vulputate faucibus id, elementum lobortis felis. Mauris urna dolor, placerat ac sagittis quis." style="text-align: left; z-index: 13;"><p>i now fully appreciate the role of lexers, whitespace and PEGs do <em>*not*</em> mix</p></div>
</div></section></section><section class="stack" data-id="078cbf3544989234f99f58c5eaf385c4"><section data-id="a2ec09b9df8f881193e02b67d9d34a6f"><div class="sl-block" data-block-type="text" style="width: 864px; left: 39.5px; top: 66px; height: auto;" data-block-id="5c70c5419a4fffc36f326389f04919b1"><div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="text-align: left; z-index: 11;"><h2>subtyping</h2></div></div>
<div class="sl-block" data-block-type="code" style="width: 881px; height: 508px; left: 39.5px; top: 160px;" data-name="code-b4c850" data-block-id="f43d7b497a44cc7a79f9799f8c957bc7"><div class="sl-block-content notranslate" data-highlight-theme="github-gist" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;" data-code-wrap="true"><pre style="font-size: 16px; line-height: 19px;" class="cpp"><code data-line-numbers="">/// The subtyping relation between any two types.
pub fn subtype(is: &amp;Type, of: &amp;Type) -&gt; bool {
    match (is, of) {
        (Type::Record(is_fields), Type::Record(of_fields)) =&gt; {
            // width, depth, and permutation
            for (key, of_value) in of_fields {
                match is_fields.get(key) {
                    Some(is_value) =&gt; if !subtype(is_value, of_value) {
                        return false;
                    },
                    None =&gt; return false
                }
            }
            return true;
        },
        (Type::Function { from: is_from, to: is_to }, 
         Type::Function { from: of_from, to: of_to }) =&gt; {
            subtype(of_from, is_from) &amp;&amp; subtype(is_to, of_to)
        }
        (Type::Natural, Type::Integer) =&gt; true, // obviously not, but let's pretend
        (_, Type::Empty) =&gt; true,
        (Type::Error, _) =&gt; true,
        (_, _) if is == of =&gt; true,
        (_, _) =&gt; false,
    }
}
</code></pre></div></div></section><section data-id="185642af785c80a8e89f91ed87071041"><div class="sl-block" data-block-type="text" style="width: 413px; left: 29px; top: 84px; height: auto;" data-block-id="509cdb304125bcb536707476b3659024"><div class="sl-block-content" data-placeholder-tag="h2" data-placeholder-text="Title Text" style="text-align: left; z-index: 11;"><h3>advanced ish types</h3></div></div>
<div class="sl-block" data-block-type="text" style="width: 413px; left: 29px; top: 165px; height: auto;" data-block-id="74b007d99173637ef45f94e4d8ee8230"><div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi nec metus justo. Aliquam erat volutpat." style="z-index: 13; text-align: left; line-height: 1.625;" data-has-line-height=""><ul>
	<li>function types</li>
	<li>structs/records/products: three types for the price of one! <span style="font-size:0.5em">(note: remove this, this isn't funny)</span>
</li>
	<li>subtyping determined with a <strong>subtype</strong> function</li>
	<li>drop-in replacement for type equality (<strong>==</strong>) in impl</li>
	<li>if branches must be mutual subtypes</li>
</ul></div></div>
<div class="sl-block" data-block-type="code" style="width: 451px; height: 548.5px; left: 480px; top: 109.5px;" data-name="code-365804" data-block-id="6b0a245087a60ebd891520e52e03c50f"><div class="sl-block-content notranslate" data-highlight-theme="ascetic" data-code-frame="none" style="z-index: 10; border-style: solid; border-width: 1px;"><pre class="ocaml" style="font-size: 16px; line-height: 19px;"><code data-line-numbers="">pub type Identifier = String;
pub type Context = 
    HashMap&lt;Identifier, Term&gt;;

pub type Value = u64;

#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Type {
    Empty,  // top
    Error,  // bottom
    Unit,
    Boolean,
    Natural,
    Integer,
    // Float,
    // String,
    Enum(Vec&lt;Type&gt;),
    Record(HashMap&lt;Identifier, Type&gt;),
    Function{from: Box&lt;Type&gt;, 
             to: Box&lt;Type&gt;
    },
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Term {
    pub val: Value,
    pub kind: Type,
}
</code></pre></div></div></section></section><section data-id="395e68419b49e56ae2c9503f9349949b"><div class="sl-block" data-block-type="text" style="width: 864px; left: 30px; top: 58px; height: auto;" data-block-id="fca8471a1c5e254df842c59786968a72"><div class="sl-block-content" data-placeholder-tag="h1" style="font-size: 200%; text-align: left; z-index: 10;" data-placeholder-text="Text"><h2>future plans<br>
</h2></div></div>
<div class="sl-block" data-block-type="text" style="height: auto; width: 850px; left: 30px; top: 245px;" data-name="text-419f61" data-block-id="03c292be5839e649ed825dbb51b4ed96"><div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Text" style="z-index: 11;"><ul>
	<li>complete and test subtyping</li>
	<li>extend system with additional higher-level types
	<ul>
		<li>enums</li>
		<li>actually distinct naturals and integers</li>
		<li>floats</li>
		<li>strings (ugh), vecs, collections of data</li>
	</ul>
	</li>
	<li>type classes (still really want to implement), needs:
	<ul>
		<li>a global context + first class functions</li>
		<li>resolving functions via identifiers</li>
	</ul>
	</li>
	<li>then, write another parser</li>
</ul></div></div></section><section data-id="0d1b641e07aaf095303a30707be1be28"><div class="sl-block" data-block-type="text" style="width: 864px; left: 30px; top: 58px; height: auto;" data-block-id="7d75ef11e0b5935bc5066a155bf24992"><div class="sl-block-content" data-placeholder-tag="h1" style="font-size: 200%; text-align: left; z-index: 10;" data-placeholder-text="Text">
<h1>Questions?<br>
 </h1>

<p>no</p>
</div></div></section><section data-id="9c412ee29000e2ef5c0d519c9144e8ab"><div class="sl-block" data-block-type="text" style="width: 910px; left: 25px; top: 299.5px; height: auto;" data-block-id="ca2a2bc628d05d54fbc85e432d1d9f09"><div class="sl-block-content" data-placeholder-tag="p" data-placeholder-text="Text" style="z-index: 11; line-height: 2.6;" data-has-line-height=""><h3><a href="https://www.youtube.com/watch?v=dQw4w9WgXcQ" target="_blank">https://github.com/j-james/chrysanthemum</a></h3></div></div></section>
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