ifthenelse evaluates both branches

[hmenke]

Brief outline of the bug

ifthenelse always evaluates both branches, regardless of the condition. It should short-circuit and only evaluate the branch that is actually taken.

Minimal working example (MWE)

\documentclass{article}
\usepackage{pgfmath}
\begin{document}
\pgfmathprint{ifthenelse(1 == 1, 1, 1/0)}
\pgfmathprint{ifthenelse(0 == 1, 1/0, 1)}
\end{document}

[muzimuzhi]

It seems some laziness support is needed, either internal to ifthenelse and ?, or public as, for example \pgfmathdeclarelazy(function|operator).

[ilayn]

Also related questions in TeX.SX

[hmenke]

The culprit lies in the fact that the definition of \pgfmathifthenelse is

\pgfmathifthenelse:
macro:#1#2#3->\pgfmathparse {#1}\let \pgfmath@argument@1 =\pgfmathresult \pgfmathparse {#2}\let \pgfmath@argument@2 =\pgfmathresult \pgfmathparse {#3}\let \pgfmath@argument@3 =\pgfmathresult \pgfmathifthenelse@ {\pgfmath@argument@1 }{\pgfmath@argument@2 }{\pgfmath@argument@3 }

So we either need some separate implementations for all functions to handle laziness or we just redefine \pgfmathifthenelse after it has been defined using \pgfmathdeclarefunction. Are there any other functions that have to evaluate their arguments lazily?

[muzimuzhi]

Are there any other functions that have to evaluate their arguments lazily?

and and or

\pgfmathprint{and(false, 1/0)}
\pgfmathprint{or(true, 1/0)}