Help with xparse \newcommand

Question

I have some images that I need to cut it up, and some to cut it down. I implemented a single solution using two \newcommand that worked, but I look for one compact solution using xparse that did not work and I can not understand why.

I will appreciate any help to correct and to improve my code below.

\documentclass[11pt]{article}

\usepackage{easyfig}

% [cut up]{file}{caption}{label}{scale} - Cut up % <== Ok
\newcommand{\ruleone}[5][.05]{%
    \Figure[trim={.0\width} {.0\height} {.0\width} {#1\height},clip,%
        width=#5\linewidth,keepaspectratio=true,%
        caption={#3},label={#4},center,here]{#2}
}

% [cut down]{file}{caption}{label}{scale} - Cut down % <== Ok
\newcommand{\ruletwo}[5][.05]{%
    \Figure[trim={.0\width} {#1\height} {.0\width} {.0\height},clip,%
        width=#5\linewidth,keepaspectratio=true,%
        caption={#3},label={#4},center,here]{#2}
}

% [cut up]{file}[cut down]{caption}{label}[scale] - Cut down % <== compile with errors
\newcommand{\onerule}[ o m o m m o ]{%
    \Figure[trim={.0\width} {ifNoValueTF{#1}{.0}{#1}\height}%
        {.0\width} {ifNoValueTF{#3}{.0}{#3}\height},clip,%
        width={ifNoValueTF{#6}{1}{#6}\linewidth},keepaspectratio=true,%
        caption={#4},label={#5},center,here]{#2}
}

\begin{document}

Here comes the images:

\ruleone[.45]{example-image-a}{First image}{label1}{.5} % <== this works

\ruletwo[.35]{example-image-a}{Second image}{label2}{.5} % <== This too

\onerule[.35]{example-image-b}{Third image}{label3}{.5}

\onerule{example-image-b}[0.45]{Third image}{label3}{.5}

\end{document}

Answer 1

In xparse, the command for defining new commands is \NewDocumentCommand instead of \newcommand. Also the second argument describing the parameters is mandatory ({...} instead of [...]) and ifNoValueTF should be \IfNoValueTF (uppercase and with a backslash).

Additionally your % at the end of the line with trim arguments suppresses a required space and the scale argument is optional ([...] instead of {...}).

Then you get

\documentclass[11pt]{article}

\usepackage{xparse,easyfig}

% [cut up]{file}{caption}{label}{scale} - Cut up % <== Ok
\newcommand{\ruleone}[5][.05]{%
    \Figure[trim={.0\width} {.0\height} {.0\width} {#1\height},clip,%
        width=#5\linewidth,keepaspectratio=true,%
        caption={#3},label={#4},center,here]{#2}
}

% [cut down]{file}{caption}{label}{scale} - Cut down % <== Ok
\newcommand{\ruletwo}[5][.05]{%
    \Figure[trim={.0\width} {#1\height} {.0\width} {.0\height},clip,%
        width=#5\linewidth,keepaspectratio=true,%
        caption={#3},label={#4},center,here]{#2}
}

% [cut up]{file}[cut down]{caption}{label}[scale] - Cut down % <== compile with errors
\NewDocumentCommand \onerule { o m o m m o }{%
    \Figure[trim={.0\width} {\IfNoValueTF{#1}{.0}{#1}\height}
        {.0\width} {\IfNoValueTF{#3}{.0}{#3}\height},clip,%
        width={\IfNoValueTF{#6}{1}{#6}\linewidth},keepaspectratio=true,%
        caption={#4},label={#5},center,here]{#2}
}

\begin{document}

Here comes the images:

\ruleone[.45]{example-image-a}{First image}{label1}{.5} % <== this works

\ruletwo[.35]{example-image-a}{Second image}{label2}{.5} % <== This too

\onerule[.35]{example-image-b}{Third image}{label3}[.5]

\onerule{example-image-b}[0.45]{Third image}{label3}[.5]

\end{document}