Text not respecting \text within NewDocumentCommand within align*

Question

Within an align* environment I have lines of the form

\Rightarrow &<\texttt{Program Code}, [a \mapsto 1, b \mapsto 2]> &\text{Rule Name}\\
\Rightarrow &<\texttt{Program Code 2}, [a \mapsto 2, b \mapsto 3]> &\text{Rule Name 2} \\

Giving

I thought of making a macro to make this much easier, of the form

\pline{Program Code}{a \mapsto 2,b \mapsto 2}{Rule name}

I want the third argument, the rule name, to be optional. If so, it shouldn't show up on the line, on the right.

I was trying to use the native ifx/else combo but I switched to the xparse package. Right now, I have this:

\NewDocumentCommand{\pline}{+m +m o}{
    \Rightarrow &<\texttt{#1}, \ensuremath{[#2]}>
    \IfValueTF{#3}
        {&\text{#3}}
}

However, the rule names do not align right. See the below demonstration:

\begin{align*}
    % Explicit Code
    \Rightarrow &<\texttt{Program Code}, [a \mapsto 1, b \mapsto 2]> &\text{Rule Name} \\
    \Rightarrow &<\texttt{Program Code 2}, [a \mapsto 2, b \mapsto 3]> &\text{Rule Name 2} \\\\
    % Commands
    \pline{Program Code}{a \mapsto 1,b \mapsto 2}{Rule Name} \\
    \pline{Program Code 2}{a \mapsto 2,b \mapsto 3}{Rule Name 2}
\end{align*}

To fix this, I put the & infront of \IfValueTF and removed it from before the \text{#3}. However, though this fixes the alignment issue, the font is still wrong and seems to stay in math mode, in spite of the \text.

How can I fix both these issues?

Minimal working example:

\documentclass[notitlepage]{report}

\usepackage{mathpazo}
\usepackage{amsmath,amssymb}
\usepackage{xparse}

\begin{document}

\NewDocumentCommand{\pline}{+m +m o}{
    \Rightarrow &<\texttt{#1}, \ensuremath{[#2]}>
    \IfValueTF{#3}
        {\&text{#3}}
}

\NewDocumentCommand{\plinealigned}{+m +m o}{
    \Rightarrow &<\texttt{#1}, \ensuremath{[#2]}>
    &\IfValueTF{#3}
        {\text{#3}}
}

\begin{align*}
    % Explicit Code
    \Rightarrow &<\texttt{Program Code}, [a \mapsto 1, b \mapsto 2]> &\text{Rule Name} \\
    \Rightarrow &<\texttt{Program Code 2}, [a \mapsto 2, b \mapsto 3]> &\text{Rule Name 2} \\\\
    % Commands
    \pline{Program Code}{a \mapsto 1,b \mapsto 2}{Rule Name} \\
    \pline{Program Code 2}{a \mapsto 2,b \mapsto 3}{Rule Name 2}\\\\
    % Commands with alignment fixed
    \plinealigned{Program Code}{a \mapsto 1,b \mapsto 2}{Rule Name} \\
    \plinealigned{Program Code 2}{a \mapsto 2,b \mapsto 3}{Rule Name 2}
\end{align*}

\end{document}

Answer 1

You need \IfValueT not \IfValueTF. You misplaced &, {&\text{#3}} not {\&text{#3}} in \pline. The o is optional argument, you need [] not {}.

\documentclass[notitlepage]{report}

\usepackage{mathpazo}
\usepackage{amsmath,amssymb}
\usepackage{xparse}

\begin{document}

\NewDocumentCommand{\pline}{+m +m o}{
    \Rightarrow &<\texttt{#1}, \ensuremath{[#2]}>
    \IfValueT{#3}
        {&\text{#3}}
}

\NewDocumentCommand{\plinealigned}{+m +m o}{
    \Rightarrow &<\texttt{#1}, \ensuremath{[#2]}>
    &\IfValueT{#3}
        {\text{#3}}
}

\begin{align*}
    % Explicit Code
    \Rightarrow &<\texttt{Program Code}, [a \mapsto 1, b \mapsto 2]> &\text{Rule Name} \\
    \Rightarrow &<\texttt{Program Code 2}, [a \mapsto 2, b \mapsto 3]> &\text{Rule Name 2} \\\\
    % Commands
    \pline{Program Code}{a \mapsto 1,b \mapsto 2}[Rule Name] \\
    \pline{Program Code 2}{a \mapsto 2,b \mapsto 3}[Rule Name 2]\\
    % Commands with alignment fixed
    \plinealigned{Program Code}{a \mapsto 1,b \mapsto 2}[Rule Name] \\
    \plinealigned{Program Code 2}{a \mapsto 2,b \mapsto 3}[Rule Name 2]
\end{align*}

\end{document}

Answer 2

There are a few errors in your code:

1. \&text should be &\text
2. \ensuremath does nothing useful
3. the argument type should be m, not +m
4. < and > aren't to be used as brackets
5. an optional argument is inside square brackets, not braces

I add some space after the \Rightarrow and use \langle and \rangle for the angle brackets. Note the different spacing. Also &&\text{} for better alignment.

\documentclass{article}
\usepackage{amsmath,amssymb}

\begin{document}

\NewDocumentCommand{\pline}{m m o}{%
  \Rightarrow{} & \langle\texttt{#1}, [#2]\rangle
  \IfValueT{#3}{&&\text{#3}}%
}

\begin{align*}
\pline{Program Code}{a \mapsto 1,b \mapsto 2}[Rule Name] \\
\pline{Program Code 2}{a \mapsto 2,b \mapsto 3}[Rule Name 2]
\end{align*}

\end{document}

Why is \ensuremath doing nothing useful? The command \pline (as written) must be used in math mode, because of \Rightarrow.

If you really want < and >, make them into the proper kind of math atoms.

\documentclass{article}
\usepackage{amsmath,amssymb}

\begin{document}

\NewDocumentCommand{\pline}{m m o}{%
  \Rightarrow{} & \mathopen<\texttt{#1}, [#2]\mathclose>
  \IfValueT{#3}{&&\text{#3}}%
}

\begin{align*}
\pline{Program Code}{a \mapsto 1,b \mapsto 2}[Rule Name] \\
\pline{Program Code 2}{a \mapsto 2,b \mapsto 3}[Rule Name 2]
\end{align*}

\end{document}