en-dash with half-sized space on either the left or the right

Question

I am looking to produce directional variants of the en-dash. A "left en-dash" should have half of ordinary inter-word spacing on its right and allow line-breaks only on its left; a "right en-dash" should have half of ordinary inter-word spacing on its left and allow line-breaks only on its right. This is intended to aid the visual parsing of parenthetical phrases: "Here - as in his other works - the composer alludes to Italian folk dances."

What is the best way to define such commands? Let's name them \ldash and \rdash.

Answer 1

You can use

\newcommand{\ldash}{--\nobreak\,\nobreak\ignorespaces}
\newcommand{\rdash}{\unskip\nobreak\,\nobreak--}

\nobreak inserts a large \penalty, discouraging (not avoiding) a line or page break at that location. A small space on the sides are offered by \,, while \unskip and \ignorespaces removes the whitespace naturally inserted between words.