<div class="gmail_quote">2012/2/29 ashok bakthavathsalam <span dir="ltr"><<a href="mailto:lifebalance@gmail.com">lifebalance@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<span style="line-height:18px;text-align:left;font-size:14px;font-family:Arial,'Liberation Sans','DejaVu Sans',sans-serif">I am looking for something similar to </span><a href="http://reference.wolfram.com/mathematica/ref/ToExpression.html" rel="nofollow" style="padding-right:0px;padding-left:0px;border-bottom-width:0px;padding-top:0px;text-align:left;border-style:initial;border-color:initial;margin-bottom:0px;padding-bottom:0px;border-top-width:0px;vertical-align:baseline;line-height:18px;margin-right:0px;color:rgb(74,107,130);font-size:14px;margin-left:0px;border-right-width:0px;font-family:Arial,'Liberation Sans','DejaVu Sans',sans-serif;text-decoration:none;margin-top:0px;border-left-width:0px;background-image:initial" target="_blank">ToExpression</a><span style="line-height:18px;text-align:left;font-size:14px;font-family:Arial,'Liberation Sans','DejaVu Sans',sans-serif"> that is available in Mathematica. I just want to convert a string to an expression, and evaluate the expression. As a first pass, my strings will include only numbers and arithmetic operators, and not even parentheses.</span><div>
<div style="text-align:left"><font face="Arial, 'Liberation Sans', 'DejaVu Sans', sans-serif"><span style="font-size:14px;line-height:18px"><br></span></font></div><div style="text-align:left"><font face="Arial, 'Liberation Sans', 'DejaVu Sans', sans-serif"><span style="font-size:14px;line-height:18px">If I need to write it, please point me in the direction of the appropriate pre-defined modules/definitions which I should use.</span></font></div>
</div></blockquote><div><br></div><div>Maybe you can use this parser for infix expressions.</div><div><a href="http://planet.racket-lang.org/package-source/soegaard/infix.plt/1/0/planet-docs/manual/index.html">http://planet.racket-lang.org/package-source/soegaard/infix.plt/1/0/planet-docs/manual/index.html</a></div>
<div><br></div><div>Here is a small example (it takes a while for the library to install - it seems it old Schematics test suite takes forever to install these days - I need to switch to a builtin one).</div><div><br></div>
<div><br></div><div>#lang at-exp racket</div><div>(require (planet soegaard/infix)</div><div> (planet soegaard/infix/parser))</div><div>(display (format "1+2*3 is ~a\n" @${1+2*3} ))</div><div><br></div><div>
(parse-expression #'here (open-input-string "1+2*3"))</div><div><br></div><div>The output will be:</div><div> 1+2*3 is 7</div><div><div> .#<syntax:6:21 (#%infix (+ 1 (* 2 3)))></div></div><div><br>
</div><div>The function parse-expression parses the expression in the string and</div><div>returns a syntax-object that resembles the output of ToExpression.</div><div><br></div><div> -- </div><div>Jens Axel Søgaard</div>
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