------------------------------------------------------------------------
-- The Agda standard library
--
-- Printing Strings During Evaluation
------------------------------------------------------------------------
{-# OPTIONS --cubical-compatible --rewriting #-}
-- see README.Debug.Trace for a use-case
module Debug.Trace where
open import Agda.Builtin.String using (String)
open import Agda.Builtin.Equality using (_≡_)
-- Postulating the `trace` function and explaining how to compile it
postulate
trace : ∀ {a} {A : Set a} → String → A → A
{-# FOREIGN GHC import qualified Debug.Trace as Debug #-}
{-# FOREIGN GHC import qualified Data.Text as Text #-}
{-# COMPILE GHC trace = const (const (Debug.trace . Text.unpack)) #-}
-- Because expressions involving postulates get stuck during evaluation,
-- we also postulate an equality characterising `trace`'s behaviour. By
-- declaring it as a rewrite rule we internalise that evaluation rule.
postulate
trace-eq : ∀ {a} {A : Set a} (a : A) str → trace str a ≡ a
{-# BUILTIN REWRITE _≡_ #-}
{-# REWRITE trace-eq #-}
-- Specialised version of `trace` returning the traced message.
traceId : String → String
traceId str = trace str str
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