Arithmetic evaluation: Difference between revisions

Left _ -> error "Did not parse"</lang>

 

A compact recursive descent parser using Hanson's device. This program

* handles left and right associativity and different precedences

* Notice that the code looks remarkably like a typical grammar, rather than being an opaque cryptic solution

* Does not rely on any library to silently solve 1/2 the problem; in fact, this code would probably suit being put into a library almost verbatim

<lang Icon>procedure main() #: simple arithmetical parser / evaluator

write("Usage: Input expression = Abstract Syntax Tree = Value, ^Z to end.")