2a: Unit Logic

++biff

Unit as argument

Applies a function b that produces a unit to the unwrapped value of ++unit a (u.a). If a is empty, ~ is produced.

Accepts

a is a unit.

b is a function that accepts a noun and produces a unit.

Produces

A unit.

Source

    ++  biff
      |*  [a](unit) b]$-(* (unit))]
      ?~  a  ~
      (b u.a)

Examples

    > (biff (some 5) |=(a]@ (some (add a 2))))
    [~ u=7]

    > (biff ~ |=(a]@ (some (add a 2))))
    ~

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++bind

Non-unit function to unit, producing unit

Applies a function b to the value (u.a) of a ++unit a, producing a unit. Used when you want a function that does not accept or produce a unit to both accept and produce a unit.

Accepts

a is a unit.

b is a function.

Produces

A unit.

Source

    ++  bind
      |*  [a=(unit) b=gate]
      ?~  a  ~
      [~ u=(b u.a)]

Examples

    > (bind ((unit @) [~ 97]) ,@t)
    [~ u='a']

    > =a |=(a]@ (add a 1))
    > (bind ((unit @) [~ 2]) a)
    [~ u=3]

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++bond

Replace null

Replaces an empty ++unit b with the product of a called trap a. If the unit is not empty, then the original unit is produced.

Accepts

a is a trap.

b is a unit.

Produces

Either the product of a or the value inside of unit b.

Source

    ++  bond
      |*  a=(trap)
      |*  b=(unit)
      ?~  b  $:a
      u.b

Examples

    > (bex 10)
    1.024
    > ((bond |.((bex 10))) ~)
    1.024

    > ((bond |.((bex 10))) (slaw %ud '123'))
    123

---

++both

Group unit values into pair

Produces ~ if either a or b are empty. Otherwise, produces a ++unit whose value is a cell of the values of two input units a and b.

Accepts

a is a unit.

b is a unit.

Produces

A unit of the two initial values.

Source

    ++  both
      |*  [a=(unit) b=(unit)]
      ?~  a  ~
      ?~  b  ~
      [~ u=[u.a u.b]]

Examples

    > (both (some 1) (some %b))
    [~ u=[1 %b]]

    > (both ~ (some %b))
    ~

---

++clap

Apply function to two units

Applies a binary function c--which does not usually accept or produce a ++unit-- to the values of two units, a and b, producing a unit.

Accepts

a is a unit.

b is a unit.

c is a function that performs a binary operation.

Produces

A unit.

Source

    ++  clap                                                ::  combine
      |*  [a](unit) b=(unit) c=_|=(^ +<-)]
      ?~  a  b
      ?~  b  a
      [~ u=(c u.a u.b)]

Examples

    > =u ((unit @t) [~ 'a'])
    > =v ((unit @t) [~ 'b'])
    > (clap u v |=([a=@t b=@t] (welp (trip a) (trip b))))
    [~ u="ab"]

    > =a ((unit @u) [~ 1])
    > =b ((unit @u) [~ 2])
    > =c |=([a=@ b=@] (add a b))

    > (clap a b c)
    [~ 3]

---

++drop

Unit to list

Makes a ++list of the unwrapped value (u.a) of a ++unit a.

Accepts

a is a unit.

Produces

A list.

Source

    ++  drop                                                ::  enlist
      |*  a=(unit)
      ?~  a  ~
      [i=u.a t=~]

Examples

    > =a ((unit @) [~ 97])
    > (drop a)
    [i=97 t=~]

    > =a ((unit @) [~])
    > (drop a)
    ~

---

++fall

Give unit a default value

Produces a default value b for a ++unit a in cases where a is null.

Accepts

a is a unit.

b is a noun that's used as the default value.

Produces

Either a noun b or the unwrapped value of unit a.

Source

    ++  fall                                                ::  default
      |*  [a=(unit) b=*]
      ?~(a b u.a)

Examples

    > (fall ~ `a`)
    `a`
    > (fall [~ u=0] `a`)
    0

---

++lift

Curried bind

Accepts a ++gate a and produces a function that accepts ++unit b to which it applies a. Used when you want a function that does not accept or produce a unit to both accept and produce a unit.

Accepts

a is a gate.

b is a unit.

Produces

A unit.

Source

    ++  lift                                                ::  lift gate (fmap)
      |*  a=gate                                            ::  flipped
      |*  b=(unit)                                          ::  curried
      (bind b a)                                            ::  bind

Examples

    > ((lift dec) `(unit @)`~)
    ~

    > ((lift dec) `(unit @)`[~ 20])
    [~ 19]

---

++mate

Choose

Accepts two units a and b whose values are expected to be equivalent. If either is empty, then the value of the other is produced. If neither are empty, it asserts that both values are the same and produces that value. If the assertion fails, ++mate crashes with 'mate' in the stack trace.

Accepts

a is a unit.

b is a unit.

Produces

A unit or crash.

Source

    ++  mate                                                ::  choose
      |*  [a=(unit) b=(unit)]
      ?~  b  a
      ?~  a  b
      ?.(=(u.a u.b) ~|('mate' !!) a)

Examples

    > =a ((unit @) [~ 97])
    > =b ((unit @) [~ 97])
    > (mate a b)
    [~ 97]

    > =a ((unit @) [~ 97])
    > =b ((unit @) [~])
    > (mate a b)
    [~ 97]

    > =a ((unit @) [~ 97])
    > =b ((unit @) [~ 98])
    > (mate a b)
    ! 'mate'
    ! exit

---

++need

Unwrap unit

Retrieve the value from a ++unit and crash if the unit is null.

Accepts

a is a unit.

Produces

Either the unwrapped value of a (u.a), or crash.

Source

    ++  need                                                ::  demand
      |*  a](unit)
      ?~  a  ~|(%need !!)
      u.a

Examples

    > =a ((unit [@t @t]) [~ ['a' 'b']])
    > (need a)
    ['a' 'b']

    > =a ((unit @ud) [~ 17])
    > (need a)
    17

    > =a ((unit @) [~])
    > (need a)
    ! exit

---

++some

Wrap value in a unit

Takes any atom a and produces a ++unit with the value set to a.

Accepts

a is a noun.

Produces

A unit.

Source

    ++  some                                                ::  lift (pure)
      |*  a=*
      [~ u=a]

Examples

    > (some [`a` `b`])
    [~ u=[`a` `b`]]

    > (some &)
    [~ u=%.y]

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