Mathematica Tutorial: Notebooks And Documents - Wolfram Research

Notebooks and Documents 105ToExpression will attempt to interpret any string as Mathematica input. But if you give it astring that does not correspond to syntactically correct input, then it will print a message, andreturn $Failed.This is not syntactically correct input, so ToExpression does not convert it to an expression.In[16]:= ToExpression@"1 +ê+ 2"DToExpression::sntx: Syntax error in or before "1 +/+ 2".^Out[16]= $FailedToExpression requires that the string correspond to a complete Mathematica expression.In[17]:= ToExpression@"1 + 2 + "DToExpression::sntxi:Incomplete expression; more input is needed.Out[17]= $FailedYou can use the function SyntaxQ to test whether a particular string corresponds to syntacticallycorrect Mathematica input. If SyntaxQ returns False, you can find out where the erroroccurred using SyntaxLength. SyntaxLength returns the number of characters which weresuccessfully processed before a syntax error was detected.SyntaxQ shows that this string does not correspond to syntactically correct Mathematica input.In[18]:= SyntaxQ@"1 +ê+ 2"DOut[18]= FalseSyntaxLength reveals that an error was detected after the third character in the string.In[19]:= SyntaxLength@"1 +ê+ 2"DOut[19]= 3Here SyntaxLength returns a value greater than the length of the string, indicating that theinput was correct so far as it went, but needs to be continued.In[20]:= SyntaxLength@"1 + 2 + "DOut[20]= 10