Assn  f Fun(
  x, 
 =>
    Var(x)
)

Assn  f Fun(
  _, 
 =>
    Var(x)
)

Assn  f Fun(
  Str("foo"), 
 =>
    Str("!")
)

Assn  f Fun(
  Bar, 
 =>
    Str("?")
)

Assn  f Fun(
  Num(55), 
 =>
    Str("~")
)

Assn  f Fun(
  Tup( ), 
 =>
    Var(x)
)

Assn  f Fun(
  Tup( x ), 
 =>
    Var(x)
)

Assn  f Fun(
  Tup( x y ), 
 =>
    Var(x)
)

Assn  f Fun(
  Tup( x y z ), 
 =>
    Var(x)
)