function to filter identical data.fames using less than (<) and greater than (>)

Esteemed UseRs,

I've got many biggish data frames which need a lot subsetting, like in 
this example:

# example
eg <- data.frame(A = rnorm(10), B = rnorm(10), C = rnorm(10), D = 
rnorm(10))
egsub <- eg[eg$A < 0 & eg$B < 1 & eg$C > 0, ]
egsub
egsub2 <- eg[eg$A > 1 & eg$B > 0, ]
egsub2

# To make this clearer than 1000s of lines of extractions with []
# I tried to make a function like this:

# func(data="eg", A="< 0", B="< 1", C="> 0")

# Which would also need to be run as

# func(data="eg", A="> 1", B="> 0", C=NA)
#end

Noteably:
-the signs* "<" and ">" need to be flexible _and_ optional
-the quantities also need to be flexible
-column header names i.e, A, B and C don't need flexibility,
i.e., can remain fixed
* "less than" and "greater than" so google picks up this thread

Once again i find just how limited my grasp of R is...Is do.call() the 
best way to call binary operators like < & > in a function? Is an 
ifelse statement needed for each column to make filtering on it 
optional? etc....

Any one with the patience to show their working version of such a 
funciton would receive my undying Rdulation. With thanks in advance,

Karl