R: Examples for 'base::formals'

### ** Examples

require(stats)
formals(lm)

$formula


$data


$subset


$weights


$na.action


$method
[1] "qr"

$model
[1] TRUE

$x
[1] FALSE

$y
[1] FALSE

$qr
[1] TRUE

$singular.ok
[1] TRUE

$contrasts
NULL

$offset


$...

## If you just want the names of the arguments, use formalArgs instead.
names(formals(lm))

 [1] "formula"     "data"        "subset"      "weights"     "na.action"  
 [6] "method"      "model"       "x"           "y"           "qr"         
[11] "singular.ok" "contrasts"   "offset"      "..."

methods:: formalArgs(lm)     # same

 [1] "formula"     "data"        "subset"      "weights"     "na.action"  
 [6] "method"      "model"       "x"           "y"           "qr"         
[11] "singular.ok" "contrasts"   "offset"      "..."

## formals returns a pairlist. Arguments with no default have type symbol (aka name).
str(formals(lm))

Dotted pair list of 14
 $ formula    : symbol 
 $ data       : symbol 
 $ subset     : symbol 
 $ weights    : symbol 
 $ na.action  : symbol 
 $ method     : chr "qr"
 $ model      : logi TRUE
 $ x          : logi FALSE
 $ y          : logi FALSE
 $ qr         : logi TRUE
 $ singular.ok: logi TRUE
 $ contrasts  : NULL
 $ offset     : symbol 
 $ ...        : symbol

## formals returns NULL for primitive functions.  Use it in combination with
## args for this case.
is.primitive(`+`)

[1] TRUE

formals(`+`)

NULL

formals(args(`+`))

$e1


$e2

## You can overwrite the formal arguments of a function (though this is
## advanced, dangerous coding).
f <- function(x) a + b
formals(f) <- alist(a = , b = 3)
f    # function(a, b = 3) a + b

function (a, b = 3) 
a + b
<environment: 0x55ccff44c098>

f(2) # result = 5

[1] 5

Examples for 'base::formals'

Access to and Manipulation of the Formal Arguments