Income tax calculator

incomeTax.ffg

\input ->

let real/greaterThan = https://raw.githubusercontent.com/Gabriella439/grace/main/prelude/real/greaterThan.ffg

let toBracket
        :  List { "Tax rate": Real, "Lower bound": Real, "Minimum tax": Real }
        -> { }
        -> Real
        -> Real
        = \brackets -> \_ -> \income ->
            List/fold
              { cons:
                  \bracket result ->
                    if real/greaterThan income bracket."Lower bound"
                    then   bracket."Minimum tax"
                         + (  bracket."Tax rate"
                           * (income + Real/negate bracket."Lower bound") : Real
                           )
                    else result
              , nil:
                  0
              }
              (List/reverse brackets)

let tax =
      merge 
      # Based on 2022 federal income tax brackets from:
      #
      # https://www.nerdwallet.com/article/taxes/federal-income-tax-brackets
      { "Single filers":
          toBracket
            [ { "Tax rate": 0.10, "Lower bound":      0.00, "Minimum tax":      0.00 }
            , { "Tax rate": 0.12, "Lower bound":  10275.00, "Minimum tax":   1027.50 }
            , { "Tax rate": 0.22, "Lower bound":  41775.00, "Minimum tax":   4807.50 }
            , { "Tax rate": 0.24, "Lower bound":  89075.00, "Minimum tax":  15213.50 }
            , { "Tax rate": 0.32, "Lower bound": 170050.00, "Minimum tax":  34647.50 }
            , { "Tax rate": 0.35, "Lower bound": 215950.00, "Minimum tax":  49335.50 }
            , { "Tax rate": 0.37, "Lower bound": 539900.00, "Minimum tax": 162718.00 }
            ]
      , "Married, filing jointly":
          toBracket
            [ { "Tax rate": 0.10, "Lower bound":      0.00, "Minimum tax":      0.00 }
            , { "Tax rate": 0.12, "Lower bound":  20550.00, "Minimum tax":   2055.00 }
            , { "Tax rate": 0.22, "Lower bound":  93550.00, "Minimum tax":   9615.00 }
            , { "Tax rate": 0.24, "Lower bound": 178150.00, "Minimum tax":  30427.00 }
            , { "Tax rate": 0.32, "Lower bound": 340100.00, "Minimum tax":  69295.00 }
            , { "Tax rate": 0.35, "Lower bound": 431900.00, "Minimum tax":  98671.00 }
            , { "Tax rate": 0.37, "Lower bound": 647850.00, "Minimum tax": 174253.50 }
            ]
      , "Married, filing separately":
          toBracket
            [ { "Tax rate": 0.10, "Lower bound":      0.00, "Minimum tax":      0.00 }
            , { "Tax rate": 0.12, "Lower bound":  10275.00, "Minimum tax":   1027.50 }
            , { "Tax rate": 0.22, "Lower bound":  41775.00, "Minimum tax":   4807.50 }
            , { "Tax rate": 0.24, "Lower bound":  89075.00, "Minimum tax":  15213.50 }
            , { "Tax rate": 0.32, "Lower bound": 170050.00, "Minimum tax":  34647.50 }
            , { "Tax rate": 0.35, "Lower bound": 215950.00, "Minimum tax":  49335.50 }
            , { "Tax rate": 0.37, "Lower bound": 539900.00, "Minimum tax": 162718.00 }
            ]
      , "Head of household":
          toBracket
            [ { "Tax rate": 0.10, "Lower bound":      0.00, "Minimum tax":      0.00 }
            , { "Tax rate": 0.12, "Lower bound":  14650.00, "Minimum tax":   1465.00 }
            , { "Tax rate": 0.22, "Lower bound":  55900.00, "Minimum tax":   6415.00 }
            , { "Tax rate": 0.24, "Lower bound":  89050.00, "Minimum tax":  13708.00 }
            , { "Tax rate": 0.32, "Lower bound": 170050.00, "Minimum tax":  33148.00 }
            , { "Tax rate": 0.35, "Lower bound": 215950.00, "Minimum tax":  47836.00 }
            , { "Tax rate": 0.37, "Lower bound": 539900.00, "Minimum tax": 161218.50 }
            ]
      }
      input."Filing status"
      input."Taxable income"

in  { "Tax": tax }