regex-parsing-examples

Some example traces through parsing regular expressions--this was useful in
figuring out what each sub-parser needed to do.

Regular expression: a|b

character    currRegex     regexStack
---------    ---------     ----------
a            a=char(a)
|            nil           option(a)
b            b=char(b)     option(a)
[end]        option(a,b)

Regular expression: ab|cd

character    currRegex     regexStack
---------    ---------     ----------
a            a=char(a)
b            b=char(b)     concat(a)
|            nil           option(ab=concat(a, b))
c            c=char(c)     option(ab)
d            d=char(d)     concat(c), option(ab)
[end]        option(ab, concat(c, d))

Regular expression: a|(bcd)

character    currRegex     regexStack
---------    ---------     ----------
a            a=char(a)
|            nil           option(a)
(            nil           paren, option(a)
b            b=char(b)     paren, option(a)
c            c=char(c)     concat(b), paren, option(a)
d            d=char(d)     concat(b,c), paren, option(a)
)            concat(b,c,d) option(a)
[end]        option(a, concat(b,c,d))

Regular expression: a(bc|d|ef)g

character    currRegex     regexStack
---------    ---------     ----------
a            a=char(a)
(            nil           paren, concat(a)
b            b=char(b)     paren, concat(a)
c            c=char(c)     concat(b), paren, concat(a)
|            nil           option(bc=concat(b, c)), paren, concat(a)
d            d=char(d)     option(bc), paren, concat(a)
|            nil           option(bc, d), paren, concat(a)
e            e=char(e)     option(bc, d), paren, concat(a)
f            f=char(f)     concat(e), option(bc, d), paren, concat(a)
)            x=option(bc, d, concat(e, f))     concat(a)
g            g=char(g)     concat(a, x)
[end]        concat(a, x, g)