Kent Johnson wrote:
On Tue, May 5, 2009 at 8:11 AM, Lie Ryan <lie.1...@gmail.com> wrote:
Bring on your hardest searches...
Nice!
The Suite class is only there to turn the NotFound sentinel from len(text)
to -1 (used len(text) since it simplifies the code a lot...)
How does this simplify the code? Why not use the 'in' operator and
return True or False from the terms?
Using len(text) as NotFound sentinel simplifies the code because, as it
was searching for the lowest index that matches the expression, I used
min((a, b)) to do the comparison, and if NotFound is -1, min((a, b))
will return -1. Since len(text) is always higher (or equal) to the other
expression and thus will not affect the comparison
in codespeak:
text = 'ABCD'
pat1 = 'C' # P('C') determined 2
pat2 = 'Z' # P('Z') determined 4/NotFound
expr = OR(P('C'), P('Z'))
# 2 or NotFound is True
# min(2, 4) is 2
pat3 = 'A' # P('A') determined 0
expr = OR(P('C'), P('A'))
# 3 or 0 is True
# min((3, 0)) is 0
pat4 = 'Y' # P('Y') determined 4/NotFound
expr = OR(P('Z'), P('Y'))
# NotFound or NotFound is False
$ min(4, 4) is 4, i.e. NotFound
Also, the 'in' operator cannot be used to handle nested expressions. On
nested expressions, I simply need to evaluate two indexes and find their
lower index (if applicable).
Other alternative sentinel I was thinking about was 0, which simplify
the if expressions, but it 1) also suffers the same problem with -1 and
2) 0 is already occupied by the first character.
I decided that having pat1 != len(text) sprinkled is simpler than
rewriting min() to special case -1 AND still had to have pat != -1
sprinkled.
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