(.require
 [library
  [lux (.except nat int rev)
   [abstract
    [hash (.only Hash)]
    [monoid (.only Monoid)]
    [equivalence (.only Equivalence)]
    [codec (.only Codec)]
    [order (.only Order)]
    [monad (.only do)]]
   [control
    ["[0]" maybe]
    ["[0]" try (.only Try)]
    [function
     [predicate (.only Predicate)]]]
   [data
    ["[0]" text]]
   [meta
    ["@" target]]]]
 ["[0]" //
  ["[1][0]" i64]
  ["[1][0]" nat]
  ["[1][0]" int]
  ["[1][0]" rev]])

(with_template [<name> <value>]
  [(def .public <name>
     <value>)]

  [e   +2.7182818284590452354]
  ... ["π is wrong!" by Bob Palais](https://www.math.utah.edu/~palais/pi.html)
  [pi  +3.14159265358979323846]
  ... [The Tau Manifesto](https://tauday.com/tau-manifesto)
  [tau +6.28318530717958647692]
  )

(for @.old
     (these (with_template [<name> <method>]
              [(def .public (<name> it)
                 (-> Frac Frac)
                 (<method> it))]

              [cos    "jvm invokestatic:java.lang.Math:cos:double"]
              [sin    "jvm invokestatic:java.lang.Math:sin:double"]
              [tan    "jvm invokestatic:java.lang.Math:tan:double"]

              [acos   "jvm invokestatic:java.lang.Math:acos:double"]
              [asin   "jvm invokestatic:java.lang.Math:asin:double"]
              [atan   "jvm invokestatic:java.lang.Math:atan:double"]
              
              [exp    "jvm invokestatic:java.lang.Math:exp:double"]
              [log    "jvm invokestatic:java.lang.Math:log:double"]
              
              [ceil   "jvm invokestatic:java.lang.Math:ceil:double"]
              [floor  "jvm invokestatic:java.lang.Math:floor:double"]

              [root_2 "jvm invokestatic:java.lang.Math:sqrt:double"]
              [root_3 "jvm invokestatic:java.lang.Math:cbrt:double"]
              )
            (def .public (pow param subject)
              (-> Frac Frac Frac)
              ("jvm invokestatic:java.lang.Math:pow:double,double" subject param)))

     @.jvm
     (these (def !double
              (template (_ value)
                [(|> value
                     (as (Primitive "java.lang.Double"))
                     "jvm object cast")]))
            
            (def !frac
              (template (_ value)
                [(|> value
                     "jvm object cast"
                     (is (Primitive "java.lang.Double"))
                     (as Frac))]))
            
            (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> !double
                      ["D"]
                      ("jvm member invoke static" [] "java.lang.Math" <method> [])
                      !frac))]

              [cos    "cos"]
              [sin    "sin"]
              [tan    "tan"]

              [acos   "acos"]
              [asin   "asin"]
              [atan   "atan"]
              
              [exp    "exp"]
              [log    "log"]
              
              [ceil   "ceil"]
              [floor  "floor"]
              
              [root_2 "sqrt"]
              [root_3 "cbrt"]
              )
            
            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (|> ("jvm member invoke static" [] "java.lang.Math" "pow" []
                   ["D" (!double subject)] ["D" (!double param)])
                  !frac)))

     @.js
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> []
                      ("js apply" ("js constant" <method>))
                      (as Frac)))]

              [cos    "Math.cos"]
              [sin    "Math.sin"]
              [tan    "Math.tan"]

              [acos   "Math.acos"]
              [asin   "Math.asin"]
              [atan   "Math.atan"]
              
              [exp    "Math.exp"]
              [log    "Math.log"]
              
              [ceil   "Math.ceil"]
              [floor  "Math.floor"]

              [root_2 "Math.sqrt"]
              [root_3 "Math.cbrt"]
              )
            
            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (as Frac ("js apply" ("js constant" "Math.pow") [subject param]))))

     @.python
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> []
                      ("python object do" <method> ("python import" "math"))
                      (as Frac)))]

              [cos    "cos"]
              [sin    "sin"]
              [tan    "tan"]

              [acos   "acos"]
              [asin   "asin"]
              [atan   "atan"]
              
              [exp    "exp"]
              [log    "log"]
              
              [ceil   "ceil"]
              [floor  "floor"]

              [root_2 "sqrt"]
              )
            
            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (as Frac ("python object do" "pow" ("python import" "math") [subject param])))

            (def .public (root_3 it)
              (-> Frac Frac)
              (if ("lux f64 <" +0.0 it)
                (|> it
                    ("lux f64 *" -1.0)
                    (..pow ("lux f64 /" +3.0 +1.0))
                    ("lux f64 *" -1.0))
                (|> it
                    (..pow ("lux f64 /" +3.0 +1.0))))))

     @.lua
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> []
                      ("lua apply" ("lua constant" <method>))
                      (as Frac)))]

              [cos    "math.cos"]
              [sin    "math.sin"]
              [tan    "math.tan"]

              [acos   "math.acos"]
              [asin   "math.asin"]
              [atan   "math.atan"]
              
              [exp    "math.exp"]
              [log    "math.log"]
              
              [ceil   "math.ceil"]
              [floor  "math.floor"]

              [root_2 "math.sqrt"]
              )
            
            (def .public (pow param subject)
              (-> Frac Frac Frac)
              ("lua power" param subject))

            (def .public (root_3 it)
              (-> Frac Frac)
              (if ("lux f64 <" +0.0 it)
                (|> it
                    ("lux f64 *" -1.0)
                    (..pow ("lux f64 /" +3.0 +1.0))
                    ("lux f64 *" -1.0))
                (|> it
                    (..pow ("lux f64 /" +3.0 +1.0))))))

     @.ruby
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> []
                      ("ruby apply" ("ruby constant" <method>))
                      (as Frac)))]

              [cos    "Math.cos"]
              [sin    "Math.sin"]
              [tan    "Math.tan"]

              [acos   "Math.acos"]
              [asin   "Math.asin"]
              [atan   "Math.atan"]
              
              [exp    "Math.exp"]
              [log    "Math.log"]
              
              [root_2 "Math.sqrt"]
              [root_3 "Math.cbrt"]
              )

            (with_template [<name> <method>]
              [(def .public (<name> it)
                 (-> Frac Frac)
                 (|> ("ruby object do" <method> it [])
                     (as Int)
                     ("lux i64 f64")))]

              [ceil  "ceil"]
              [floor "floor"]
              )

            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (as Frac ("ruby object do" "**" subject [param]))))

     @.php
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> ("php apply" ("php constant" <method>))
                      (as Frac)))]

              [cos    "cos"]
              [sin    "sin"]
              [tan    "tan"]

              [acos   "acos"]
              [asin   "asin"]
              [atan   "atan"]
              
              [exp    "exp"]
              [log    "log"]

              [ceil   "ceil"]
              [floor  "floor"]
              
              [root_2 "sqrt"]
              )

            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (as Frac ("php apply" ("php constant" "pow") subject param)))

            (def .public root_3
              (-> Frac Frac)
              (..pow ("lux f64 /" +3.0 +1.0))))

     @.scheme
     (these (with_template [<name> <method>]
              [(def .public <name>
                 (-> Frac Frac)
                 (|>> ("scheme apply" ("scheme constant" <method>))
                      (as Frac)))]

              [cos    "cos"]
              [sin    "sin"]
              [tan    "tan"]

              [acos   "acos"]
              [asin   "asin"]
              [atan   "atan"]
              
              [exp    "exp"]
              [log    "log"]

              [ceil   "ceiling"]
              [floor  "floor"]
              
              [root_2 "sqrt"]
              )

            (def .public (pow param subject)
              (-> Frac Frac Frac)
              (as Frac ("scheme apply" ("scheme constant" "expt") subject param)))

            (def .public root_3
              (-> Frac Frac)
              (..pow ("lux f64 /" +3.0 +1.0))))
     )

(def .public (round it)
  (-> Frac Frac)
  (let [floored (floor it)
        diff ("lux f64 -" floored it)]
    (cond ("lux f64 <" diff +0.5)
          ("lux f64 +" +1.0 floored)
          
          ("lux f64 <" -0.5 diff)
          ("lux f64 +" -1.0 floored)
          
          ... else
          floored)))

(def .public (atan_2 x y)
  (-> Frac Frac Frac)
  (cond ("lux f64 <" x +0.0)
        (..atan ("lux f64 /" x y))

        ("lux f64 <" +0.0 x)
        (if (or ("lux f64 <" y +0.0)
                ("lux f64 =" +0.0 y))
          (|> y ("lux f64 /" x) atan ("lux f64 +" pi))
          (|> y ("lux f64 /" x) atan ("lux f64 -" pi)))

        ... ("lux f64 =" +0.0 x)
        (cond ("lux f64 <" y +0.0)
              (|> pi ("lux f64 /" +2.0))
              
              ("lux f64 <" +0.0 y)
              (|> pi ("lux f64 /" -2.0))
              
              ... ("lux f64 =" +0.0 y)
              ("lux f64 /" +0.0 +0.0))))

(def .public (log_by base it)
  (-> Frac Frac Frac)
  ("lux f64 /"
   (..log base)
   (..log it)))

(def .public (factorial it)
  (-> Nat Nat)
  (loop (again [acc 1
                it it])
    (if (//nat.> 1 it)
      (again (//nat.* it acc) (-- it))
      acc)))

(def .public (hypotenuse catA catB)
  (-> Frac Frac Frac)
  (..pow +0.5 ("lux f64 +"
               (..pow +2.0 catA)
               (..pow +2.0 catB))))

... Hyperbolic functions
... https://en.wikipedia.org/wiki/Hyperbolic_function#Definitions
(with_template [<name> <comp> <inverse>]
  [(def .public (<name> it)
     (-> Frac Frac)
     (|> (..exp it) (<comp> (..exp ("lux f64 *" -1.0 it))) ("lux f64 /" +2.0)))

   (def .public (<inverse> it)
     (-> Frac Frac)
     (|> +2.0 ("lux f64 /" (|> (..exp it) (<comp> (..exp ("lux f64 *" -1.0 it)))))))]

  [sinh "lux f64 -" csch]
  [cosh "lux f64 +" sech]
  )

(with_template [<name> <top> <bottom>]
  [(def .public (<name> it)
     (-> Frac Frac)
     (let [e+ (exp it)
           e- (exp ("lux f64 *" -1.0 it))
           sinh' (|> e+ ("lux f64 -" e-))
           cosh' (|> e+ ("lux f64 +" e-))]
       (|> <top> ("lux f64 /" <bottom>))))]

  [tanh sinh' cosh']
  [coth cosh' sinh']
  )

... https://en.wikipedia.org/wiki/Inverse_hyperbolic_functions#Definitions_in_terms_of_logarithms
(with_template [<name> <comp>]
  [(def .public (<name> it)
     (-> Frac Frac)
     (|> it (pow +2.0) (<comp> +1.0) (pow +0.5) ("lux f64 +" it) log))]

  [asinh "lux f64 +"]
  [acosh "lux f64 -"]
  )

(with_template [<name> <base> <diff>]
  [(def .public (<name> it)
     (-> Frac Frac)
     (let [it+ (|> <base> ("lux f64 +" <diff>))
           it- (|> <base> ("lux f64 -" <diff>))]
       (|> it+ ("lux f64 /" it-) log ("lux f64 /" +2.0))))]

  [atanh +1.0 it]
  [acoth it +1.0]
  )

(with_template [<name> <op>]
  [(def .public (<name> it)
     (-> Frac Frac)
     (let [it^2 (|> it (pow +2.0))]
       (|> +1.0 (<op> it^2) (pow +0.5) ("lux f64 +" +1.0) ("lux f64 /" it) log)))]

  [asech "lux f64 -"]
  [acsch "lux f64 +"]
  )

(with_template [<name> <op>]
  [(def .public (<name> param subject)
     (-> Frac Frac Bit)
     (<op> param subject))]

  [= "lux f64 ="]
  [< "lux f64 <"]
  )

(def .public (<= reference sample)
  (-> Frac Frac Bit)
  (or ("lux f64 <" reference sample)
      ("lux f64 =" reference sample)))

(def .public (> reference sample)
  (-> Frac Frac Bit)
  ("lux f64 <" sample reference))

(def .public (>= reference sample)
  (-> Frac Frac Bit)
  (or ("lux f64 <" sample reference)
      ("lux f64 =" sample reference)))

(with_template [<comparison> <name>]
  [(def .public <name>
     (Predicate Frac)
     (<comparison> +0.0))]

  [..> positive?]
  [..< negative?]
  [..= zero?]
  )

(with_template [<name> <op>]
  [(def .public (<name> param subject)
     (-> Frac Frac Frac)
     (<op> param subject))]

  [+ "lux f64 +"]
  [- "lux f64 -"]
  [* "lux f64 *"]
  [/ "lux f64 /"]
  [% "lux f64 %"]
  )

(def .public (/% param subject)
  (-> Frac Frac [Frac Frac])
  [(../ param subject)
   (..% param subject)])

(def .public opposite
  (-> Frac Frac)
  (..* -1.0))

(def .public (abs it)
  (-> Frac Frac)
  (if (..< +0.0 it)
    (..* -1.0 it)
    it))

(def .public (signum it)
  (-> Frac Frac)
  (cond (..= +0.0 it) +0.0
        (..< +0.0 it) -1.0
        ... else
        +1.0))

(def min_exponent -1022)
(def max_exponent (//int.frac +1023))

(with_template [<name> <test>]
  [(def .public (<name> left right)
     (-> Frac Frac Frac)
     (if (<test> right left)
       left
       right))]

  [min ..<]
  [max ..>]
  )

(def .public nat
  (-> Frac Nat)
  (|>> "lux f64 i64" .nat))

(def .public int
  (-> Frac Int)
  (|>> "lux f64 i64"))

(def mantissa_size Nat 52)
(def exponent_size Nat 11)

(def frac_denominator
  (|> -1
      ("lux i64 right-shift" ..exponent_size)
      "lux i64 f64"))

(def .public rev
  (-> Frac Rev)
  (|>> ..abs
       (..% +1.0)
       (..* ..frac_denominator)
       "lux f64 i64"
       ("lux i64 left-shift" ..exponent_size)))

(with_template [<name> <numerator>]
  [(def .public <name>
     Frac
     (../ +0.0 <numerator>))]

  [not_a_number      +0.0]
  [positive_infinity +1.0]
  )

(def .public negative_infinity
  Frac
  (..* -1.0 ..positive_infinity))

(def .public (not_a_number? it)
  (-> Frac Bit)
  (not (..= it it)))

(def .public (number? it)
  (-> Frac Bit)
  (not (or (..not_a_number? it)
           (..= ..positive_infinity it)
           (..= ..negative_infinity it))))

(def .public equivalence
  (Equivalence Frac)
  (implementation
   (def (= left right)
     (or (..= left right)
         (and (..not_a_number? left)
              (..not_a_number? right))))))

(def .public order
  (Order Frac)
  (implementation
   (def equivalence ..equivalence)
   (def < ..<)))

(def .public smallest
  Frac
  (..pow (//int.frac (//int.- (.int ..mantissa_size) ..min_exponent))
         +2.0))

(def .public biggest
  Frac
  (let [f2^-52 (..pow (//nat.frac (//nat.- ..mantissa_size 0)) +2.0)
        f2^+1023 (..pow ..max_exponent +2.0)]
    (|> +2.0
        (..- f2^-52)
        (..* f2^+1023))))

(with_template [<name> <composite> <identity>]
  [(def .public <name>
     (Monoid Frac)
     (implementation
      (def identity <identity>)
      (def composite <composite>)))]

  [addition       ..+   +0.0]
  [multiplication ..*   +1.0]
  [minimum        ..min ..biggest]
  [maximum        ..max (..* -1.0 ..biggest)]
  )

(def .public decimal
  (Codec Text Frac)
  (implementation
   (def (encoded x)
     (case x
       -0.0 (let [output ("lux f64 encode" x)]
              (if (text.starts_with? "-" output)
                output
                ("lux text concat" "+" output)))
       _ (if (..< +0.0 x)
           ("lux f64 encode" x)
           ("lux text concat" "+" ("lux f64 encode" x)))))

   (def (decoded input)
     (case ("lux f64 decode" input)
       {.#Some value}
       {try.#Success value}

       {.#None}
       {try.#Failure "Could not decode Frac"}))))

(def log/2
  (-> Frac Frac)
  (|>> ..log
       (../ (..log +2.0))))

(def double_bias Nat 1023)

(def exponent_mask (//i64.mask ..exponent_size))

(def exponent_offset ..mantissa_size)
(def sign_offset (//nat.+ ..exponent_size ..exponent_offset))

(with_template [<cast> <hex> <name>]
  [(def <name>
     (|> <hex>
         (at //nat.hex decoded)
         try.trusted
         <cast>))]

  [.i64 "FFF8000000000000" not_a_number_bits]
  [.i64 "7FF0000000000000" positive_infinity_bits]
  [.i64 "FFF0000000000000" negative_infinity_bits]
  [.i64 "0000000000000000" positive_zero_bits]
  [.i64 "8000000000000000" negative_zero_bits]
  [.nat "7FF"              special_exponent_bits]
  )

(def smallest_exponent
  (..log/2 ..smallest))

(def .public (bits it)
  (-> Frac I64)
  (.i64 (cond (..not_a_number? it)
              ..not_a_number_bits

              (..= positive_infinity it)
              ..positive_infinity_bits

              (..= negative_infinity it)
              ..negative_infinity_bits

              (..= +0.0 it)
              (let [reciprocal (../ it +1.0)]
                (if (..= positive_infinity reciprocal)
                  ... Positive zero
                  ..positive_zero_bits
                  ... Negative zero
                  ..negative_zero_bits))

              ... else
              (let [sign_bit (if (..< +0.0 it)
                               1
                               0)
                    it (..abs it)
                    exponent (|> it
                                 ..log/2
                                 ..floor
                                 (..min ..max_exponent))
                    min_gap (..- (//int.frac ..min_exponent) exponent)
                    power (|> (//nat.frac ..mantissa_size)
                              (..+ (..min +0.0 min_gap))
                              (..- exponent))
                    max_gap (..- ..max_exponent power)
                    mantissa (|> it
                                 (..* (..pow (..min ..max_exponent power) +2.0))
                                 (..* (if (..> +0.0 max_gap)
                                        (..pow max_gap +2.0)
                                        +1.0)))
                    exponent_bits (|> (if (..< +0.0 min_gap)
                                        (|> (..int exponent)
                                            (//int.- (..int min_gap))
                                            --)
                                        (..int exponent))
                                      (//int.+ (.int ..double_bias))
                                      (//i64.and ..exponent_mask))
                    mantissa_bits (..int mantissa)]
                (all //i64.or
                     (//i64.left_shifted ..sign_offset sign_bit)
                     (//i64.left_shifted ..exponent_offset exponent_bits)
                     (//i64.zero ..mantissa_size mantissa_bits)))
              )))

(with_template [<getter> <size> <offset>]
  [(def <getter>
     (-> (I64 Any) I64)
     (let [mask (|> 1 (//i64.left_shifted <size>) -- (//i64.left_shifted <offset>))]
       (|>> (//i64.and mask) (//i64.right_shifted <offset>) .i64)))]

  [mantissa ..mantissa_size 0]
  [exponent ..exponent_size ..mantissa_size]
  [sign     1               ..sign_offset]
  )

(def .public (of_bits it)
  (-> I64 Frac)
  (case [(is Nat (..exponent it))
         (is Nat (..mantissa it))
         (is Nat (..sign it))]
    [..special_exponent_bits 0 0]
    ..positive_infinity

    [..special_exponent_bits 0 1]
    ..negative_infinity

    [..special_exponent_bits _ _]
    ..not_a_number

    ... Positive zero
    [0 0 0] +0.0
    ... Negative zero
    [0 0 1] (..* -1.0 +0.0)

    [E M S]
    (let [sign (if (//nat.= 0 S)
                 +1.0
                 -1.0)
          [mantissa power] (if (//nat.< ..mantissa_size E)
                             [(if (//nat.= 0 E)
                                M
                                (//i64.one ..mantissa_size M))
                              (|> E
                                  (//nat.- ..double_bias)
                                  .int
                                  (//int.max ..min_exponent)
                                  (//int.- (.int ..mantissa_size)))]
                             [(//i64.one ..mantissa_size M)
                              (|> E (//nat.- ..double_bias) (//nat.- ..mantissa_size) .int)])
          exponent (..pow (//int.frac power) +2.0)]
      (|> (//nat.frac mantissa)
          (..* exponent)
          (..* sign)))))

(`` (def (representation_exponent codec representation)
      (-> (Codec Text Nat) Text (Try [Text Int]))
      (case [("lux text index" 0 "e+" representation)
             ("lux text index" 0 "E+" representation)
             ("lux text index" 0 "e-" representation)
             ("lux text index" 0 "E-" representation)]
        (,, (with_template [<factor> <pattern>]
              [<pattern>
               (do try.monad
                 [.let [after_offset (//nat.+ 2 split_index)
                        after_length (//nat.- after_offset ("lux text size" representation))]
                  exponent (|> representation
                               ("lux text clip" after_offset after_length)
                               (at codec decoded))]
                 (in [("lux text clip" 0 split_index representation)
                      (//int.* <factor> (.int exponent))]))]

              [+1 [{.#Some split_index} {.#None} {.#None} {.#None}]]
              [+1 [{.#None} {.#Some split_index} {.#None} {.#None}]]
              
              [-1 [{.#None} {.#None} {.#Some split_index} {.#None}]]
              [-1 [{.#None} {.#None} {.#None} {.#Some split_index}]]))
        
        _
        {try.#Success [representation +0]})))

(with_template [<struct> <nat> <int> <error>]
  [(def .public <struct>
     (Codec Text Frac)
     (implementation
      (def (encoded value)
        (let [bits (..bits value)
              mantissa (..mantissa bits)
              exponent (//int.- (.int ..double_bias) (..exponent bits))
              sign (..sign bits)]
          (all "lux text concat"
               (case (.nat sign)
                 1 "-"
                 0 "+"
                 _ (undefined))
               (at <nat> encoded (.nat mantissa))
               ".0E"
               (at <int> encoded exponent))))

      (def (decoded representation)
        (let [negative? (text.starts_with? "-" representation)
              positive? (text.starts_with? "+" representation)]
          (if (or negative? positive?)
            (do [! try.monad]
              [[mantissa exponent] (..representation_exponent <nat> representation)
               [whole decimal] (case ("lux text index" 0 "." mantissa)
                                 {.#Some split_index}
                                 (do !
                                   [.let [after_offset (++ split_index)
                                          after_length (//nat.- after_offset ("lux text size" mantissa))]
                                    decimal (|> mantissa
                                                ("lux text clip" after_offset after_length)
                                                (at <nat> decoded))]
                                   (in [("lux text clip" 0 split_index mantissa)
                                        decimal]))

                                 {.#None}
                                 {try.#Failure ("lux text concat" <error> representation)})
               .let [whole ("lux text clip" 1 (-- ("lux text size" whole)) whole)]
               mantissa (at <nat> decoded (case decimal
                                            0 whole
                                            _ ("lux text concat" whole (at <nat> encoded decimal))))
               .let [sign (if negative? 1 0)]]
              (in (..of_bits
                   (all //i64.or
                        (//i64.left_shifted ..sign_offset (.i64 sign))
                        (//i64.left_shifted ..mantissa_size (.i64 (//int.+ (.int ..double_bias) exponent)))
                        (//i64.zero ..mantissa_size (.i64 mantissa))))))
            {try.#Failure ("lux text concat" <error> representation)})))))]

  [binary //nat.binary //int.binary "Invalid binary syntax: "]
  [octal //nat.octal //int.octal "Invalid octaladecimal syntax: "]
  [hex //nat.hex //int.hex "Invalid hexadecimal syntax: "]
  )

(def .public hash
  (Hash Frac)
  (implementation
   (def equivalence ..equivalence)
   (def hash ..bits)))

(def .public (approximately? margin_of_error standard value)
  (-> Frac Frac Frac Bit)
  (|> value
      (..- standard)
      ..abs
      (..< margin_of_error)))

(def .public (mod divisor dividend)
  (All (_ m) (-> Frac Frac Frac))
  (let [remainder (..% divisor dividend)]
    (if (or (and (..< +0.0 divisor)
                 (..> +0.0 remainder))
            (and (..> +0.0 divisor)
                 (..< +0.0 remainder)))
      (..+ divisor remainder)
      remainder)))