From: Nokan Emiro <uzleepito@...>
Date: 2013-01-25T02:30:52+09:00
Subject: building expressions in strings

--e89a8ff252ee0ff17104d40c1458
Content-Type: text/plain; charset=UTF-8

Hi list,

In my program I need to combine together two Ruby expressions with
a binary operator or apply an unary one on an expression.  The expressions
are given in strings and the returned expression is a String too.

def binary(exp1, op, exp2)
  if %i[ + - * ** & | && || ].member? op
    "(#{exp1}) #{op} (#{exp2})" # infix format
  else
    "(#{exp1}).#{op}(#{exp2})" # method call format
  end
end


I would like to know if there's a simple way to eliminate the safety
parentheses
if they are not necessary.  binary("1 + 1", :*, "2 + 2") needs the
parentheses, but
binary("1 + 1", :+, "2 + 2") doesn't.

Can Ripper or any additional gem elevate the main operator (I mean the
operator that would
be evaluated lastly) in an expression to make it possible to check
precedence?

How do I know if I really need the parentheses before the . in the method
call format line?

--e89a8ff252ee0ff17104d40c1458
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

Hi list,<div><br></div><div>In my program I need to combine together two Ru=
by expressions with</div><div>a binary operator or apply an unary one on an=
 expression. =C2=A0The expressions</div><div>are given in strings and the r=
eturned expression is a String too.</div>
<div><br></div><blockquote class=3D"webkit-indent-blockquote" style=3D"marg=
in:0 0 0 40px;border:none;padding:0px"><div><font class=3D"Apple-style-span=
" face=3D"&#39;courier new&#39;, monospace">def binary(exp1, op, exp2)</fon=
t></div>
<div><font class=3D"Apple-style-span" face=3D"&#39;courier new&#39;, monosp=
ace">=C2=A0 if %i[ + - * ** &amp; | &amp;&amp; || ].member? op</font></div>=
<div><font class=3D"Apple-style-span" face=3D"&#39;courier new&#39;, monosp=
ace">=C2=A0 =C2=A0 &quot;(#{exp1}) #{op} (#{exp2})&quot; # infix format</fo=
nt></div>
<div><font class=3D"Apple-style-span" face=3D"&#39;courier new&#39;, monosp=
ace">=C2=A0 else</font></div><div><font class=3D"Apple-style-span" face=3D"=
&#39;courier new&#39;, monospace">=C2=A0 =C2=A0=C2=A0&quot;(#{exp1}).#{op}(=
#{exp2})&quot; # method call format</font></div>
<div><font class=3D"Apple-style-span" face=3D"&#39;courier new&#39;, monosp=
ace">=C2=A0 end</font></div><div><font class=3D"Apple-style-span" face=3D"&=
#39;courier new&#39;, monospace">end</font></div></blockquote><div><br></di=
v><div>I would like to know if there&#39;s a simple way to eliminate the sa=
fety parentheses</div>
<div>if they are not necessary. =C2=A0binary(&quot;1 + 1&quot;, :*, &quot;2=
 + 2&quot;) needs the parentheses, but</div><div>binary(&quot;1 + 1&quot;, =
:+, &quot;2 + 2&quot;) doesn&#39;t.</div><div><br></div><div>Can Ripper or =
any additional gem elevate the=C2=A0main operator (I mean the operator that=
 would</div>
<div>be evaluated lastly) in an expression to=C2=A0make it possible to chec=
k precedence?</div><div><br></div><div>How do I know if I really need the p=
arentheses before the . in the method call format line?</div><div><br></div=
>
<div><br></div>

--e89a8ff252ee0ff17104d40c1458--