Is there a way to use whitespace in BNFC?

Question

How do you use whitespace in a BNFC definition?

For example, suppose I want to produce a parser for the lambda calculus where I allow a list of variables to be abstracted:

\x y z.x z (y z)

The "obvious" thing to do is use a labeled rule like:

ListAbs . Exp ::= "\\" [Ident] "." Exp ;
separator Ident " "

However, BNFC defaults to stripping whitespace, so that does not work. What does work is using a comma separator. A bit uglier, but I could live with it... Still it would be nice to be able to separate by space.

Is there a whitespace character class in BNFC?

Answer 1

You can declare the empty string as separator:

separator Ident ""

In practice this lets you use white-spaces (or any space character) as separator:

$ cat test.cf
A . A ::= [Ident] ;
separator Ident ""
$ bnfc -haskell -m test.cf
$ make
$ echo 'x y z' | ./Testtest

Parse Successful!

[Abstract Syntax]

A [Ident "x",Ident "y",Ident "z"]

[Linearized tree]

x y z