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copied!<h2>Perl (no eval)</h2> <p><strong>Number of characters: <s>167</s> 106</strong> (see below for the 106 character version)</p> <p>Fully obfuscated function: (167 characters if you join these three lines into one)</p> <pre><code>sub e{my$_="($_[0])";s/\s//g;$n=q"(-?\d++(\.\d+)?+)"; @a=(sub{$1},1,sub{$3*$6},sub{$3+$6},4,sub{$3-$6},6,sub{$3/$6}); while(s:\($n\)|(?<=\()$n(.)$n:$a[7&ord$5]():e){}$_} </code></pre> <p>Clear/deobfuscated version:</p> <pre><code>sub e { my $_ = "($_[0])"; s/\s//g; $n=q"(-?\d++(\.\d+)?+)"; # a regex for "number", including capturing groups # q"foo" in perl means the same as 'foo' # Note the use of ++ and ?+ to tell perl # "no backtracking" @a=(sub{$1}, # 0 - no operator found 1, # placeholder sub{$3*$6}, # 2 - ord('*') = 052 sub{$3+$6}, # 3 - ord('+') = 053 4, # placeholder sub{$3-$6}, # 5 - ord('-') = 055 6, # placeholder sub{$3/$6}); # 7 - ord('/') = 057 # The (?<=... bit means "find a NUM WHATEVER NUM sequence that happens # immediately after a left paren", without including the left # paren. The while loop repeatedly replaces "(" NUM WHATEVER NUM with # "(" RESULT and "(" NUM ")" with NUM. The while loop keeps going # so long as those replacements can be made. while(s:\($n\)|(?<=\()$n(.)$n:$a[7&ord$5]():e){} # A perl function returns the value of the last statement $_ } </code></pre> <p>I had misread the rules initially, so I'd submitted a version with "eval". Here's a version without it.</p> <p>The latest bit of insight came when I realized that the last octal digit in the character codes for <code>+</code>, <code>-</code>, <code>/</code>, and <code>*</code> is different, and that <code>ord(undef)</code> is 0. This lets me set up the dispatch table <code>@a</code> as an array, and just invoke the code at the location <code>7 & ord($3)</code>. </p> <p>There's an obvious spot to shave off one more character - change <code>q""</code> into <code>''</code> - but that would make it harder to cut-and-paste into the shell.</p> <h2>Even shorter</h2> <p><strong>Number of characters: <s>124</s> 106</strong></p> <p>Taking edits by <a href="https://stackoverflow.com/users/20713">ephemient</a> into account, it's now down to 124 characters: (join the two lines into one)</p> <pre><code>sub e{$_=$_[0];s/\s//g;$n=q"(-?\d++(\.\d+)?+)"; 1while s:\($n\)|$n(.)$n:($1,1,$3*$6,$3+$6,4,$3-$6,6,$6&&$3/$6)[7&ord$5]:e;$_} </code></pre> <h2>Shorter still</h2> <p><strong>Number of characters: <s>110</s> 106</strong></p> <p>The ruby solution down below is pushing me further, though I can't reach its 104 characters:</p> <pre><code>sub e{($_)=@_;$n='( *-?[.\d]++ *)'; s:\($n\)|$n(.)$n:(($1,$2-$4,$4&&$2/$4,$2*$4,$2+$4)x9)[.8*ord$3]:e?e($_):$_} </code></pre> <p>I had to give in and use <code>''</code>. That ruby <code>send</code> trick is really useful for this problem.</p> <h2>Squeezing water from a stone</h2> <p><strong>Number of characters: 106</strong></p> <p>A small contortion to avoid the divide-by-zero check.</p> <pre><code>sub e{($_)=@_;$n='( *-?[.\d]++ *)'; s:\($n\)|$n(.)$n:($1,0,$2*$4,$2+$4,0,$2-$4)[7&ord$3]//$2/$4:e?e($_):$_} </code></pre> <p>Here's the test harness for this function:</p> <pre><code>perl -le 'sub e{($_)=@_;$n='\''( *-?[.\d]++ *)'\'';s:\($n\)|$n(.)$n:($1,0,$2*$4,$2+$4,0,$2-$4)[7&ord$3]//$2/$4:e?e($_):$_}' -e 'print e($_) for @ARGV' '1 + 3' '1 + ((123 * 3 - 69) / 100)' '4 * (9 - 4) / (2 * 6 - 2) + 8' '2*3*4*5+99' '2.45/8.5*9.27+(5*0.0023) ' '1 + 3 / -8' </code></pre>

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