This affects all your minted
environments. One work around is to set \fboxsep
to 0pt
in the definition of minted@colorbg
as follows.
\makeatletter
\renewenvironment{minted@colorbg}[1]{
\setlength{\fboxsep}{\z@}
\def\minted@bgcol{#1}
\noindent
\begin{lrbox}{\minted@bgbox}
\begin{minipage}{\linewidth}}
{\end{minipage}
\end{lrbox}%
\colorbox{\minted@bgcol}{\usebox{\minted@bgbox}}}
\makeatother
Here is a full minimal working example (MWE). (You should construct one in succeeding posts for speedier replies. A lot of answerers do not like to work from scratch.)
\documentclass[preview,border=5]{standalone}
\usepackage{minted}
\makeatletter
\renewenvironment{minted@colorbg}[1]{
\setlength{\fboxsep}{\z@}
\def\minted@bgcol{#1}
\noindent
\begin{lrbox}{\minted@bgbox}
\begin{minipage}{\linewidth}}
{\end{minipage}
\end{lrbox}%
\colorbox{\minted@bgcol}{\usebox{\minted@bgbox}}}
\makeatother
\definecolor{dhscodebg}{rgb}{0.95,0.95,0.95}
\newminted[dhscode]{hs}{tabsize=4, fontsize=\footnotesize, frame=lines, framesep=5\fboxrule,framerule=1pt,
bgcolor=dhscodebg, rulecolor=\color{gray!40}}
\begin{document}
\begin{dhscode}
foo :: Double -> Int
\end{dhscode}
\end{document}
