perga/lib/Errors.hs

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
    | DuplicateDefinition 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) = "Axiom '" ++ T.unpack x ++ "' missing type ascription"
    show (DuplicateDefinition n) = "'" ++ T.unpack n ++ "' already defined"

type Result = Either Error