The Parse command accepts a string containing a Maple-syntax math expression, and returns an inert-form expression.  

By parsing to inert form you can avoid automatic simplification that is normally done on mathematical expressions.  For example, parsing "1+1" using the parse command will give you the answer 2, because Maple automatically simplifies expressions where multiple integer constants are added.  Using this parser, the same "1+1" will give %+(1,1), where the terms are all present in a form that can be easily manipulated in a predictable way.  For more information on automatic simplification, refer to the Maple Expressions chapter of the Maple Programming Guide.

The inert form rewrites the following (normally infix) operators: *, +, ^, /.   It also prefixes all function calls with a percent character.

Note that the unary negation operator is not rewritten.  Parse of "-x" will return -x, and Parse of "a-b" will return %+(a,-b). Similarly Parse of "-a+b" will return %+(-a,b), so there is no ambiguity, and an inert minus is not necessary, except in the case of -0, which will be parsed to %*(0,-1).

If a string contains multiple expressions separated by a semicolon, only the first expression is parsed.  The lastread option can be used to find the character position of the last character included in the parsed result.  Pass an unevaluated name, lastread='n', and the designated name will be assigned the integer position.  This option should not be used in combination with implicitmultiply because some transformations are done to the string prior to true parsing, the offset returned will be unreliable.

An explicit space, such as in the expressions "2 x", or "x y", or "x 2", or "(x+4) y", is interpreted by Parse as multiplication.

A number followed by a variable or open parenthesis with no space, such as "2x", or "2(x-4)" is interpreted as multiplication between the number and subsequent expression.

Two back-to-back expressions surrounded by parentheses, such as "(x-1)(x+1)" is interpreted as multiplication between expressions.

Multi-letter variable names, if not otherwise specified by either the names or corenames options are interpreted as single letter variables multiplied together.  Thus "xy" is parsed as "x*y", but "norm(x)" is also interpreted as "n*o*r*m*x".

This function is part of the InertForm package, so it can be used in the short form Parse(..) only after executing the command with(InertForm). However, it can always be accessed through the long form of the command by using InertForm[Parse](..).

$\mathrm{ex}≔\mathrm{InertForm}:-\mathrm{Parse}\left(''(1+2)/6''\right)$

$\mathrm{ex}≔\frac{1+2}{6}$

$\mathrm{lprint}\left(\mathrm{ex}\right)$

(1 %+ 2) %/ 6

$\mathrm{value}\left(\mathrm{ex}\right)$

$\frac{1}{2}$

$\mathrm{op}\left(0\,\mathrm{ex}\right)$

$\mathrm{`/`}$

$\mathrm{op}\left(1\,\mathrm{ex}\right)$

$1+2$

$\mathrm{op}\left(\left[1\,0\right]\,\mathrm{ex}\right)$

$\mathrm{`+`}$

$\mathrm{op}\left(\left[1\,1\right]\,\mathrm{ex}\right)$

$1$

$\mathrm{op}\left(\left[1\,2\right]\,\mathrm{ex}\right)$

$2$

$\mathrm{op}\left(2\,\mathrm{ex}\right)$

$6$

$\mathrm{Student}:-\mathrm{Basics}:-\mathrm{ExpandSteps}\left(\frac{a^2-1}{\frac{1}{3}a+\frac{1}{3}}\right)$

$\begin{array}{c}\frac{a^2-1}{\frac{a}{3}+\frac{1}{3}}\\ \=\frac{\left(a+1\right)\cdot \left(a-1\right)}{\left(a+1\right)\cdot \left(\frac{1}{3}\right)}& \left(\text{Factor}\right)\\ \=\frac{a-1}{\frac{1}{3}}& \left(\text{divide}\right)\\ \=\left(a-1\right)\cdot \left(\frac{3}{1}\right)& \left(\text{Rewrite division as multiplication by reciprocal}\right)\\ \=3a-3& \left(\text{Multiply fraction and reduce by gcd}\right)\end{array}$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''cx2''\,'\mathrm{implicitmultiply}'\right)$

$c\ast x\ast 2$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''c\; x\; 2''\,'\mathrm{implicitmultiply}'\right)$

$c\ast x\ast 2$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''cx2''\,'\mathrm{implicitmultiply}'\,\mathrm{names}=''all''\right)$

$\mathrm{cx2}$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''cx2''\,'\mathrm{implicitmultiply}'\,\mathrm{names}=\left\{\mathrm{x2}\right\}\right)$

$c\ast \mathrm{x2}$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''phi1phi2''\,'\mathrm{implicitmultiply}'\,\mathrm{names}=\left\{\mathrm{\phi }\,\mathrm{\φ1}\,\mathrm{\φ2}\right\}\right)$

$\mathrm{\φ1}\ast \mathrm{\φ2}$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''abcd''\,'\mathrm{implicitmultiply}'\,\mathrm{names}=\left\{\mathrm{ab}\,\mathrm{abc}\,\mathrm{cd}\right\}\right)$

$\mathrm{abc}\ast d$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''varx^2''\,'\mathrm{implicitmultiply}'\,\mathrm{names}=\left\{\mathrm{var}\right\}\right)$

$\mathrm{var}\ast x^2$

$\mathrm{InertForm}:-\mathrm{Parse}\left(''f(\backslash "a\; b\; c\backslash ")''\,\mathrm{implicitmultiply}\right)$

$f\left(''a\; b\; c''\right)$

The InertForm[Parse] command was introduced in Maple 18.

For more information on Maple 18 changes, see Updates in Maple 18.