plonky2-verifier/src/Gate/Vars.hs

-- | Variables appearing in gate constraints

module Gate.Vars where

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import Text.Show

import Algebra.Expr
import Misc.Pretty

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-- * Constraint variables

-- | These index into a row + public input
data PlonkyVar
  = SelV   Int        -- ^ selector variable
  | ConstV Int        -- ^ constant variable
  | WireV  Int        -- ^ wire variable
  | PIV    Int        -- ^ public input hash variable (technically these are constants, not variables)
  deriving (Eq,Ord,Show)

instance Pretty PlonkyVar where
  prettyPrec _ v = case v of
    SelV   k -> showString ("s" ++ show k)
    ConstV k -> showString ("c" ++ show k)
    WireV  k -> showString ("w" ++ show k)
    PIV    k -> showString ("h" ++ show k)

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-- * Variables

data Var v
  = LocalVar Int String      -- ^ a temporary variable
  | ProofVar v               -- ^ a proof variable (eg. witness, constant, selector)
  deriving (Eq,Show)

instance Pretty v => Pretty (Var v) where
  prettyPrec d var = case var of
    LocalVar k name -> showString ("_" ++ name ++ show k)
    ProofVar v      -> prettyPrec d v

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-- * Convenience

wire, cnst, hash :: Int -> Expr (Var PlonkyVar)
wire i = VarE $ ProofVar $ WireV  i       -- witness variable
cnst i = VarE $ ProofVar $ ConstV i       -- constant variable
hash i = VarE $ ProofVar $ PIV    i       -- public input hash component

wireExt :: Int -> Expr (Var PlonkyVar)
wireExt i = wire i + ImgE (wire (i+1))    -- use two consecutive variables as an extension field element

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