perga/lib/Errors.hs

module Errors where

import Expr
import Prettyprinter
import Prettyprinter.Render.Text
import Prelude hiding (group)

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

instance Pretty Error where
    pretty (UnboundVariable x) = "Unbound variable: '" <> pretty x <> "'"
    pretty (NotASort x) = group $ hang 4 ("Term:" <> line <> pretty x) <> line <> "is not a type"
    pretty (ExpectedPiType x t) = group $ hang 4 ("Term:" <> line <> pretty x) <> line <> hang 4 ("is not a function, instead is type" <> line <> pretty t)
    pretty (NotEquivalent a a' e) =
        group $
            hang 4 ("Cannot unify" <> line <> pretty a)
                <> line
                <> hang 4 ("with" <> line <> pretty a')
                <> line
                <> hang 4 ("when evaluating" <> line <> pretty e)
    pretty (PNMissingType x) = "Axiom '" <> pretty x <> "' missing type ascription"
    pretty (DuplicateDefinition n) = "'" <> pretty n <> "' already defined"

instance ToText Error where
    toText = renderStrict . layoutSmart (LayoutOptions (AvailablePerLine 100 1.0)) . pretty

instance ToString Error where
    toString = toString . toText

type Result = Either Error