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There is a bug in the preprocessor with repspect to filtering out comments.

The following:

startshape MAKER
blah blah blah
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r 4}}
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r -4}}

...generates an error, as expected, on line 2.

The following:

startshape MAKER
// blah blah blah
# blah blah blah
/* blah blah blah */
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r 4}}
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r -4}}

...works as expected (all 3 "blah" lines are ignored)./

BUT, the following errors exit

ERROR #1:

The follwing will generate a syntax error if there is no line feed on the end of the last line:

startshape MAKER
// blah blah blah
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r 4}}
// rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r -4}}

ERROR #2:

The second rule will be active (i.e. not be ignored) if there is no line feed on the end of the last line:

startshape MAKER
// blah blah blah
rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r 4}}
# rule MAKER { TRIANGLE{} MAKER {s 0.9 y 1 r -4}}

I imagine both errors are related.

They are both caused by lex/flex not being able to skip past a line comment that ends with an end-of-file instead of a line-feed. We have known about this limitation in the lex grammar for a while. Rather than try to fix the lex grammar I put in a fix to always tack a line-feed at the end of the cfdg file.

I've been editing CFDG files in Textmate for the syntax highlighting and rendering in Context Free for the iterative display, and this bug was killing me until I figured it out. I'm glad to see a post about it here.

In 2.0, it still dies with most unhelpful error messages - is the appended-line-feed fix in 2.1b? And when is the line added - on save, or on render?

The linefeed fix is in 2.1b only, not 2.0. The linefeed is added on at the render, so it is OK if Textmate doesn't add on a linefeed.