module Errors where

import Data.Text (Text)
import qualified Data.Text as T
import Expr

data Error
    = SquareUntyped
    | UnboundVariable Text
    | NotASort Expr Expr
    | ExpectedPiType Expr Expr
    | NotEquivalent Expr Expr Expr
    | PNMissingType Text
    deriving (Eq, Ord)

instance Show Error where
    show SquareUntyped = "□ does not have a type"
    show (UnboundVariable x) = "Unbound variable: " ++ T.unpack x
    show (NotASort x t) = "Expected " ++ prettyS x ++ " to have type * or □, instead found " ++ prettyS t
    show (ExpectedPiType x t) = prettyS x ++ " : " ++ prettyS t ++ " is not a function"
    show (NotEquivalent a a' e) = "Cannot unify " ++ prettyS a ++ " with " ++ prettyS a' ++ " when evaluating " ++ prettyS e
    show (PNMissingType x) = "Primitive Notion " ++ T.unpack x ++ " missing type ascription"

type Result = Either Error