Recursive Descent Parser

Question

The book \'Modern Compiler Design\' is the nice book about compilers. In its source code something that is annoying me is AST or Abstract Syntax Tree. Suppose we want to wri

Answer 1

The answer to the question depends on whether you want a compiler, an interpreter, or something in between (an interpreter wrapped around an intermediate language). If you want an interpreter, a recursive descent parser will at the same time evaluate the expression, so there is no need to hold it in memory. If you want a compiler, then a constant expression like the example can and should be optimised, but most expressions will operate on variables, and you need to convert to tree form as an intermediate step before converting to a linear form.

A hybrid compiler / interpreter will usually compile expressions, but it doesn't have to. It's often a cheap way of writing a program which outputs an executable to simply wrap the interpreter up with the source code. Matlab uses this technique - code used to be genuinely compiled but there were problems with consistency with the interactive version. However I wouldn't allow the difficulty of generating a parse tree for expressions determine the issue.