\documentclass[acmsmall]{acmart}

% Use the UTF-8 encoding.
\usepackage[utf8]{inputenc}

% Support for Agda code.
\usepackage{agda}

% Code should be indented.
\setlength{\mathindent}{1em}

% Customised setup for certain characters.
\usepackage{newunicodechar}
\newunicodechar{∀}{\ensuremath{\mathnormal{\forall}}}
\newunicodechar{₁}{\ensuremath{{}_{\textsf{1}}}}

% Support for Greek letters.
\usepackage{alphabeta}

% Disable ligatures that start with '-'. Note that this affects the
% entire document! Note also that if all you want to do is to ensure
% that the comment starter '--' is typeset with two characters, then
% you do not need this command, because '--' is not typeset as an en
% dash (–) when the typewriter font is used.
\DisableLigatures[-]{encoding=T1}

\begin{document}
\acmConference{Some conference}
\maketile

Some code:
\begin{code}
{-# OPTIONS --without-K --count-clusters #-}

open import Agda.Builtin.String

-- A comment with some TeX ligatures:
-- --, ---, ?`, !`, `, ``, ', '', <<, >>.

Θ₁ : Set → Set
Θ₁ = λ A → A

a-name-with--hyphens : ∀ {A : Set} → A → A
a-name-with--hyphens ff--fl = ff--fl

ffi : String
ffi = "--"
\end{code}
Note that the code is indented.

\end{document}