infix operators on steroids

gistfile1.txt

Not sure exactly how useful that would be but that'd be a fun small package.

The following `infix` function parses an expression containing 
multiple infix operators so we can do things like `infix(x %is_between% y %and% z)`, i.e an "infix operation" with more than 2 parameters.

See example.

The name `infix` is not great.

```
infix <- function(x) {
  x <- substitute(x)
  args <- alist()
  funs <- character(0)
  while(length(x) > 1 && grepl("^\\%.*\\%$",deparse(x[[1]]))){
    args <- c(x[[3]], args)
    funs <- c(gsub("%","",deparse(x[[1]]),fixed=TRUE),funs)
    x <- x[[2]]
  }
  fun <- paste(funs, collapse="/")
  args <- c(x, args)
  eval.parent(rlang::expr((!!as.name(fun))(!!!args)))
  }

# define function using "/" separator
`is_between/and` <- function(x,y,z) {between(x,y,z)}

# infix will parse the expression and call the relevant function
x <- 5
y <- 1
z <- 10
infix(x %is_between% y %and% z)
# [1] TRUE
x <- 12
infix(x %is_between% y %and% z)
# [1] FALSE
```

I think regular infix operators like %in% can still be used if the expression is wrapped inside force or identity, but it isn't tested.