How does a parser for the infix notation detect the missing multiplication sign?

问题

I am writing a parser that parses mathematical expressions based on a syntax diagram very similar to this one.

I have not found a way to handle a missing multiplication sign (for example in 3(x+y)). Where in the syntax diagram do I have to handle this?

回答1:

You'd make the * optional in the definition of term.

ASCII diagram:

o-->-->--[factor]->-->--o
    /               \
    \               /
     ---<--[*]--<---
         \     /
          --<--

来源：https://stackoverflow.com/questions/31629984/how-does-a-parser-for-the-infix-notation-detect-the-missing-multiplication-sign