[NTG-context] removing whitespace

In the example below I pass the macro a string with a space, but the space should not appear in the url. I've tried using \ctxlua to invoke string substitution, but without success. What is the proper way to remove this space, and to perform string manipulation more generally? \setupinteraction[state=start] \def\squeeze#1% {\goto{#1}[url(tel:#1)]} \starttext Call \squeeze{01234 56789} \stoptext -- With kind regards, Michael