modify ast tree

[alperyilmaz]

Hi,
My aim is to replace & with function min() and replace | with max(). So, a & (b | c) should be rewritten as min(a, max(b,c)). I thought modifying the syntax tree is the way to go. Is it possible to modify ast() output and then convert back into an expression?

I'm sharing a small example:

a <- 5
b <- 10
c <- 4
express <- a & (b | c)
express_adv <- (c & b) & (a & (b | c))

The rewritten express should evaluate to 5 and express_adv should evaluate to 4. Expected expressions are :

min(a, max(b,c))  # modified express 
min( min(c,b), min(a, max(b,c)))  # modified express_adv

So, this is before:

ast( a & (b | c) )

█─`&` 
├─a 
└─█─`(` 
  └─█─`|` 
    ├─b 
    └─c 

and this is after:

ast(min(a,(max(b,c))))

█─min 
├─a 
└─█─`(` 
  └─█─max 
    ├─b 
    └─c 

[hadley]

ast() just prints the AST; it already exists in R in a way you can work with. See https://adv-r.hadley.nz/expressions.html#ast-funs for some details.