Hcfyk

I'm trying to define a macro which grabs everything until the next # (parameter token).

My twisted imagination wants something like this:

deftest#1###2{(#1)[#2]}

test hello#{world}

to grab hello in #1 (delimited by #) and world in #2 (brace delimited) and then print

(hello)[world]

However I'm failing (miserably) because no matter what combination of ## I try, TeX yells back:

! Parameters must be numbered consecutively.

<to be read again> 

                   ##

l.1 deftest#1##

                 #2{(#1)[#2]}

?

so I guess that simply writing down the # in there is not the way to go.

Is it possible somehow to have a #-delimited macro?

The TeXbook, page 203, says in the first doubly dangerous paragraph

Now that we have seen a number of examples, let’s look at the precise rules that govern TeX macros. Definitions have the general form

def⟨control sequence⟩⟨parameter text⟩{⟨replacement text⟩}

where the ⟨parameter text⟩ contains no braces, and where all occurrences of { and } in the ⟨replacement text⟩ are properly nested. Furthermore the # symbol has a special significance: In the ⟨parameter text⟩, the first appearance of # must be followed by 1, the next by 2, and so on; up to nine #’s are allowed.

There is no way for the parameter text to contain a (category code 6) #, because of the rule stated above.

As usual in the TeXbook, this is not the complete truth; in the second doubly dangerous bend on page 204 one reads

A special extension is allowed to these rules: If the very last character of the ⟨parameter text⟩ is #, so that this # is immediately followed by {, TeX will behave as if the { had been inserted at the right end of both the parameter text and the replacement text. For example, if you say ‘defa#1#{hbox to #1}’, the subsequent text ‘a3pt{x}’ will expand to ‘hbox to 3pt{x}’, because the argument
of a is delimited by a left brace.

However, this special extension has no favorable consequence towards your aim.

You can't really do what you ask, but you can ignore the # while parsing the arguments, then get rid of it:

deftest#1#{deftmp##1{#11}zz}

defzz#1{(tmp{})[#1]}



test hello#{world}



bye