\[\begin{split}\newcommand{\as}{\kw{as}}
\newcommand{\case}{\kw{case}}
\newcommand{\cons}{\textsf{cons}}
\newcommand{\consf}{\textsf{consf}}
\newcommand{\emptyf}{\textsf{emptyf}}
\newcommand{\End}{\kw{End}}
\newcommand{\kwend}{\kw{end}}
\newcommand{\even}{\textsf{even}}
\newcommand{\evenO}{\textsf{even}_\textsf{O}}
\newcommand{\evenS}{\textsf{even}_\textsf{S}}
\newcommand{\Fix}{\kw{Fix}}
\newcommand{\fix}{\kw{fix}}
\newcommand{\for}{\textsf{for}}
\newcommand{\forest}{\textsf{forest}}
\newcommand{\Functor}{\kw{Functor}}
\newcommand{\In}{\kw{in}}
\newcommand{\ind}[3]{\kw{Ind}~[#1]\left(#2\mathrm{~:=~}#3\right)}
\newcommand{\Indp}[4]{\kw{Ind}_{#4}[#1](#2:=#3)}
\newcommand{\Indpstr}[5]{\kw{Ind}_{#4}[#1](#2:=#3)/{#5}}
\newcommand{\injective}{\kw{injective}}
\newcommand{\kw}[1]{\textsf{#1}}
\newcommand{\length}{\textsf{length}}
\newcommand{\letin}[3]{\kw{let}~#1:=#2~\kw{in}~#3}
\newcommand{\List}{\textsf{list}}
\newcommand{\lra}{\longrightarrow}
\newcommand{\Match}{\kw{match}}
\newcommand{\Mod}[3]{{\kw{Mod}}({#1}:{#2}\,\zeroone{:={#3}})}
\newcommand{\ModImp}[3]{{\kw{Mod}}({#1}:{#2}:={#3})}
\newcommand{\ModA}[2]{{\kw{ModA}}({#1}=={#2})}
\newcommand{\ModS}[2]{{\kw{Mod}}({#1}:{#2})}
\newcommand{\ModType}[2]{{\kw{ModType}}({#1}:={#2})}
\newcommand{\mto}{.\;}
\newcommand{\nat}{\textsf{nat}}
\newcommand{\Nil}{\textsf{nil}}
\newcommand{\nilhl}{\textsf{nil\_hl}}
\newcommand{\nO}{\textsf{O}}
\newcommand{\node}{\textsf{node}}
\newcommand{\nS}{\textsf{S}}
\newcommand{\odd}{\textsf{odd}}
\newcommand{\oddS}{\textsf{odd}_\textsf{S}}
\newcommand{\ovl}[1]{\overline{#1}}
\newcommand{\Pair}{\textsf{pair}}
\newcommand{\plus}{\mathsf{plus}}
\newcommand{\SProp}{\textsf{SProp}}
\newcommand{\Prop}{\textsf{Prop}}
\newcommand{\return}{\kw{return}}
\newcommand{\Set}{\textsf{Set}}
\newcommand{\Sort}{\mathcal{S}}
\newcommand{\Str}{\textsf{Stream}}
\newcommand{\Struct}{\kw{Struct}}
\newcommand{\subst}[3]{#1\{#2/#3\}}
\newcommand{\tl}{\textsf{tl}}
\newcommand{\tree}{\textsf{tree}}
\newcommand{\trii}{\triangleright_\iota}
\newcommand{\Type}{\textsf{Type}}
\newcommand{\WEV}[3]{\mbox{$#1[] \vdash #2 \lra #3$}}
\newcommand{\WEVT}[3]{\mbox{$#1[] \vdash #2 \lra$}\\ \mbox{$ #3$}}
\newcommand{\WF}[2]{{\mathcal{W\!F}}(#1)[#2]}
\newcommand{\WFE}[1]{\WF{E}{#1}}
\newcommand{\WFT}[2]{#1[] \vdash {\mathcal{W\!F}}(#2)}
\newcommand{\WFTWOLINES}[2]{{\mathcal{W\!F}}\begin{array}{l}(#1)\\\mbox{}[{#2}]\end{array}}
\newcommand{\with}{\kw{with}}
\newcommand{\WS}[3]{#1[] \vdash #2 <: #3}
\newcommand{\WSE}[2]{\WS{E}{#1}{#2}}
\newcommand{\WT}[4]{#1[#2] \vdash #3 : #4}
\newcommand{\WTE}[3]{\WT{E}{#1}{#2}{#3}}
\newcommand{\WTEG}[2]{\WTE{\Gamma}{#1}{#2}}
\newcommand{\WTM}[3]{\WT{#1}{}{#2}{#3}}
\newcommand{\zeroone}[1]{[{#1}]}
\end{split}\]
Creating new tactics
The languages presented in this chapter allow one to build complex
tactics by combining existing ones with constructs such as
conditionals and looping. While Ltac was initially
thought of as a language for doing some basic combinations, it has
been used successfully to build highly complex tactics as well, but
this has also highlighted its limits and fragility. The experimental
language Ltac2 is a typed and more principled variant
which is more adapted to building complex tactics.
There are other solutions beyond these two tactic languages to write
new tactics:
Mtac2 is an external plugin
which provides another typed tactic language. While Ltac2 belongs
to the ML language family, Mtac2 reuses the language of Coq itself
as the language to build Coq tactics.
The most traditional way of building new complex tactics is to write
a Coq plugin in OCaml. Beware that this also requires much more
effort and commitment. A tutorial for writing Coq plugins is
available in the Coq repository in doc/plugin_tutorial.