agda/notes/records

What do we want?
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∙ declaration syntax
    record Point : Set where
      x : Nat
      y : Nat

∙ constructor
    record { x = 4; y = 2 }

∙ projection functions
    dist = x p ^ 2 + y p ^ 2

∙ open
    open module P = Point p
    dist = sqrt (x ^ 2 + y ^ 2)

∙ η
  p ≡ record { x = x p; y = y p }

∙ pattern matching
    f (record { x = suc n }) = n

∙ record update syntax
    how?
    record p { x = zero } ?

Schedule
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First
  ∙ declaration systax
  ∙ constructor
  ∙ projection functions
  ∙ open

Next
  ∙ η

Later
  ∙ pattern matching
  ∙ update syntax

What does it mean?
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data Point : Set where
  <Point> : (x : Nat)(y : Nat) -> Point

module Point (p : Point) where
  x : Nat
  x = <magic>

  y : Nat
  y = <magic>

Issues
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∙ mutual records? yes
  will it be a problem? probably not