All right, I think I've solved the expansion problem I= described before: to ensure that the first input is expanded when it is pa= ssed to Lua, I have to pass it as [=3D=3D[#1]=3D=3D], not "#1". B= ut the updated MWE below still does not seem to work, as the \DoIfPrefixEls= e macro is printing "NOP" instead of "YES":

```

\starttexdefini= tion loc [#1]

\doifassignmentelse{#1} { =

% if an assignment, th= en parse and format accordingly

\getparameters[loc][#1= ]

% Was a section number= specified?

\doifdefined{locsec} {=

=C2=A7 \locsec

}

} {

% otherwise, just prin= t the input as-is

}

\stoptexdefinition

\def\DoIfPrefixElse#1#2{\ctxlu= a{commands.doifelse(string.find([=3D=3D[#2]=3D=3D],"^"..[=3D=3D[#= 1]=3D=3D]))}}

\def\currentbtxloctext{\loc[se= c=3D31]}

\starttext

\currentbtxloctext\blank

\DoIfPrefixElse{=C2=A7}{\c= urrentbtxloctext}{YES}{NOP}

\stoptext

```

Indeed, if I add a simple \doifelse=C2=A0equality check, it loo= ks like the value I expect is not the same as what the macro produces, even= though they look identical:

```

\starttexdefinition loc [#1]
=C2= =A0 =C2=A0 \doifassignmentelse{#1} {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 % if a= n assignment, then parse and format accordingly
=C2=A0 =C2=A0 =C2=A0 =C2= =A0 \getparameters[loc][#1]
=C2=A0 =C2=A0 =C2=A0 =C2=A0 % Was a section = number specified?
=C2=A0 =C2=A0 =C2=A0 =C2=A0 \doifdefined{locsec} {=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A7 \locsec
=C2=A0 =C2=A0 = =C2=A0 =C2=A0 }
=C2=A0 =C2=A0 } {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 % other= wise, just print the input as-is
=C2=A0 =C2=A0 =C2=A0 =C2=A0 #1
=C2= =A0 =C2=A0 }
\stoptexdefinition

\def\DoIfPrefixElse#1#2{\ctxlua{c= ommands.doifelse(string.find([=3D=3D[#2]=3D=3D],"^"..[=3D=3D[#1]= =3D=3D]))}}

\def\currentbtxloctext{\loc[sec=3D31]}

\starttext=
=C2=A0 =C2=A0 =C2=A7 31\blank%the raw text we expect
=C2=A0 =C2=A0 \= currentbtxloctext\blank%the text as produced by the macro
=C2=A0 =C2=A0 = \doifelse{\currentbtxloctext}{=C2=A7 31}{YES}{NOP}\blank% should output YES= , but doesn't
=C2=A0 =C2=A0 \DoIfPrefixElse{=C2=A7}{\currentbtxlocte= xt}{YES}{NOP}\blank% should output YES, but doesn't
\stoptext

```

What am I missing here?

Joey

On Fri, Nov 26, 2021 at 11:57 AM Joey McCollum <= ;jmccollum20140511@gmail.com= > wrote:

=
Thanks! Invoking=C2=A0string.find(str,"^"..pre) = is certainly much easier. This sort of thing would be a nice general-purpos= e helper function. Denis Maier and I should have a "wish list" of= desired helpers and features (mostly related to bibliographies/publication= support) ready for you (and Alan) sometime soon.

But fo= r now, it looks like I still need to work out errors that arise when I pass= a macro as the "str" input to be searched. I've defined a \l= oc macro that accepts an assignment and outputs a formatted string, and lat= er, I want to check if this macro (after it has been fully expanded) starts= with a certain prefix. A minimal (non-)working example follows:
=
```
\starttexdef= inition loc [#1]
\doifa= ssignmentelse{#1} {
= % if an assignment, then parse and format accordingly
\getparameters[loc][#1]
% Was a section number specified?=
\doifdefined{locs= ec} {
=C2=A7 \l= ocsec\btxcomma
} <= /p>
} {
% otherwise, just print the input as-i= s
#1
}
\stoptexdefinition

\def\DoIfPrefi= xElse#1#2{\ctxlua{commands.doifelse(string.find("#2","^"= ;.."#1"))}}

<= /p>
\def\currentbtxloctext{\loc= [sec=3D31]}

\starttext
\DoIfPrefixElse{=C2=A7}{\currentbtxloctext}{YES}{= NOP}
\stoptext
```
=

Lua is throwing an "invalid escape sequence near '"\l'" error, which i= s presumably because the macro \loc[sec=3D31] is not being expanded. How do I fix this?
<= span style=3D"white-space:pre-wrap">
Thanks!

Joey

On Fri, Nov 26, 2021 at 3:46 AM Hans Hagen via ntg-context <ntg-context@ntg.nl&= gt; wrote:
On 11= /26/2021 7:42 AM, Joey McCollum via ntg-context wrote:
> I wasn't aware of a general-purpose "doifstartswith" mac= ro in ConTeXt
> (the \doifnextcharelse macro only works one character at a time, and t= he
> \doifinstring=C2=A0macros may capture substrings that are not prefixes= ), and
> I'd like to develop one for something I'm working on. I've= been trying
> to do this in Lua, as that seemed like the most natural approach.
> Normally, something like this would work fine as a foundation:
>
> ```
>=C2=A0 =C2=A0 function isprefix(prefix, str)
>=C2=A0 =C2=A0 =C2=A0 if string.sub(str, 1, string.len(prefix)) =3D=3D p= refix then
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 return true
>=C2=A0 =C2=A0 =C2=A0 end
>=C2=A0 =C2=A0 =C2=A0 return false
>=C2=A0 =C2=A0 end
> ```

how about

if string.find(str,"^"..prefix) then

in:

\starttext

\def\DoIfPrefixElse#1#2{\ctxlua{commands.doifelse(string.find("#2"= ;,"^".."#1"))}}

\DoIfPrefixElse{pre}{prefix}{YES}{NOP}
\DoIfPrefixElse{pre}{suffix}{YES}{NOP}

\stoptext

utf strings are just sequences of bytes so matching works

when you want to do more in lua you can decide for

\startluacode
interfaces.implement {
=C2=A0 =C2=A0 =C2=A0name=C2=A0 =C2=A0 =C2=A0 =3D "DoIfPrefixElse"= ,
=C2=A0 =C2=A0 =C2=A0arguments =3D { "argument", "argument&qu= ot; },
=C2=A0 =C2=A0 =C2=A0actions=C2=A0 =C2=A0=3D function(pre,str)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0commands.doifelse(string.find(str,"^= "..pre))
=C2=A0 =C2=A0 =C2=A0end
}
\stopluacode

\DoIfPrefixElse{pre}{prefix}{YES}{NOP}
\DoIfPrefixElse{pre}{suffix}{YES}{NOP}

but in any case: make sure that you don't clash with built in ...

if needed i can make a set of fast(er) ones but someone has to collect a list of 'handy helpers' first

Hans

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