regex start-of-line

[spir]

Hello,

I have a regex bug in following conditions: users pass a series of regex 
formats (strings) from which I create regex engines later used for lexing. To 
ensure matching at start of (rest of) source, I prefix each format with '^'. 
Right in most cases. But the following regex:
	`^(true)|(false)`
matches "false" anywhere in text ==> bug. Is this normal? There is a kind of 
ambiguity here, isn't there?

As a workaround, I replaced:
         this.engine = Regex("^" ~ form);
by
         this.engine = Regex(format("^(%s)", form));
And indeed
	`^((true)|(false))`
does not match "false" anywhere else as at start of source.

Comments?

Denis
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