Testing for floating point and int in expl3

Question

I cannot figure out how to test if an argument is a floating point or integer using expl3.

Take this simple example where I convert \milk{number} into \dotfill, the number, and gallon or gallons with or without the s appropriately, or a special case for 0, empty. The last line, for Albert, causes an error with the classic cryptic error message:

! Use of \??? doesn't match its definition.
<argument> \???  
      ! LaTeX Error: Unknown fp word none.
l.28 Albert has \milk{none}

By testing if #1 is in fact a floating point, I think I would be able to handle this error, but \tl_is_fp or even \tl_is_int don't seem to exist. How can I test if any arbitrary argument is a floating point or integer?

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand{\milk}{m}{%
    \fp_compare:nTF {#1 = 0}{%if 0 replace with empty
        \dotfill ~ empty%
    }{\fp_compare:nTF {#1 <= 1}{% s or no s
        \dotfill ~ #1~gallon%
        }{\dotfill ~ #1~gallons%
        }
    }
}

\ExplSyntaxOff

\begin{document}

Ron has \milk{0}

Tom has \milk{1/2}

Timy has \milk{1}

John has \milk{2}

Albert has \milk{-}

\end{document}

I don't think you want to test for an int (a different type0 but test if the floating point is an integer (so floor(x)=x) — David Carlisle
– David Carlisle, Commented May 6 at 22:57
do you want to test if the argument is an int or if it is an expression which evaluates to an integer? an int is, basically, a tex count. so to test if something is an int is to test whether it is something created (at the tex level) by \newcount (which is what \int_new:N does with some extra checks etc.). so 2 is not an int. don't you really want to know whether the argument is equal to an integer? — cfr
– cfr, Commented May 7 at 5:06
@mico while I was hoping to avoid needing to do that or to use any other packages, I might expand my search. Thank you for the suggestions. — Bob
– Bob, Commented May 9 at 18:10
yes, there are no real differences in kind, as I understand it, between the different types of expl3 variable. but there is a difference between an int, a dim and a tl, for example. if you try latexdef \l_tmpa_int, you can see it is \count25 i.e. it is not a macro but a register. whereas latexdef \l_tmpa_tl shows it is a macro. I don't know if this counts as a difference between data types in the sense of other programming languages, but these are different at the tex level. \def\tempa{0} creates a macro - not a count. — cfr
– cfr, Commented May 9 at 19:44
to determine whether something can be parsed as an integer, you can examine it character by character to ensure each token is a number. but to determine whether something can be parsed as an fp is harder because not only might you have, say abs(9*3-100), but you might also have user-defined functions. so distinguishing whether it can be evaluated as an fp without trying to evaluate it as an fp looks tricky to me? — cfr
– cfr, Commented May 9 at 19:48

Mico · Accepted Answer · 2025-05-10 03:01:48Z

(Added a paragraph about what to do with a negative-number input.)

Here's a LuaLaTeX-based solution. It uses Lua's tonumber function.

It is assumed that if the argument of \milk is a number (or evaluates to a number; e.g., math.abs(-1-1) evaluates to 2), this number is non-negative. I didn't add an explicit test for negative-number input as the OP's code fragment doesn't seem to consider this possibility either. Providing such a test would consist of adding an if s<0 then return "no milk." else ... end structure, starting on a new line right after the s = tonumber ( s ) line.

% !TEX TS-program = lualatex
\documentclass{article}
\directlua{

  function milk ( s )
    if tonumber ( s ) then % -- s is a number or evaluates to a number
      s = tonumber ( s )
      if s == math.floor ( s ) then % -- s is an integer
        s = math.floor ( s )
        if s == 0 then
          return "an empty bucket."
        elseif s == 1 then 
          return "1 gallon of milk."
        else 
          return s .. " gallons of milk."
        end
      else
        return s .. " gallons of milk."
      end
    else % -- s is not a number
      return "no milk."
    end
  end

}
\newcommand{\milk}[1]{\directlua{tex.sprint(milk(#1))}}

\begin{document}
\obeylines % just for this example
Ron    has \milk{"0"}
Sandra has \milk{4/5}
Timmy  has \milk{1}
Ursula has \milk{math.abs(-1-1)}
Victor has \milk{no_milk_today} % with apologies to Herman's Hermits 

Wanda  has \milk{"."}
\end{document}

When I saw the OP question, I immediately thought, "Probably better with LuaLaTeX" and hoped that someone would provide that solution. Shazam! — rallg
– rallg, Commented May 9 at 21:41

Stack Exchange Network

Testing for floating point and int in expl3

1 Answer 1

You must log in to answer this question.

Hot Network Questions

Testing for floating point and int in expl3

1 Answer 1

You must log in to answer this question.

Related

Hot Network Questions