INITIALPATH:7:22: error: • Ambiguous type variable ‘t0’ arising from a use of ‘pyfToString’ prevents the constraint ‘(PyFToString t0)’ from being solved. Probable fix: use a type annotation to specify what ‘t0’ should be. These potential instances exist: instance [safe] PyFToString String -- Defined in ‘PyF.Class’ ...plus two instances involving out-of-scope types (use -fprint-potential-instances to see them all) • In the second argument of ‘(.)’, namely ‘pyfToString’ In the expression: (PyF.Formatters.formatString (PyF.Internal.QQ.newPaddingKForString PyF.Internal.QQ.PaddingDefaultK)) Nothing . pyfToString In the first argument of ‘putStrLn’, namely ‘(((PyF.Formatters.formatString (PyF.Internal.QQ.newPaddingKForString PyF.Internal.QQ.PaddingDefaultK)) Nothing . pyfToString) (truncate number))’ | 7 | main = putStrLn [fmt|{truncate number:s}|] | ^^^^^^^^^^^^^^^^^^^^^