case

The classical case form.

Takes a 'key' and then look at arrays until it finds one that contains the key. When found, it executes the child immediately following the winning array.

case level
  [ 0 1 2 ]; 'low'
  [ 3 4 5 ]; 'medium'
  else; 'high'

which is a ";"ed version of

case level
  [ 0 1 2 ]
  'low'
  [ 3 4 5 ]
  'medium'
  else
  'high'

Non-array values are OK:

case level
  0; 'zero'
  1; 'one'
  else; 'dunno'

else

As seen in the example above, an "else" in lieu of an array acts as a catchall and the child immediately following it is executed.

If there is no else and no matching array, the case terminates and doesn't set the field "ret".

v.matched and $(matched)

When it successfully matches, the matched value (the argument of the "case") is placed in the local (local to the then or else branch) variables under 'matched'.

case 6
  5; 'five'
  [ 1, 6 ]; v.matched
  else; 'zilch'
# returns, well, 6...

case 6
  5; 'five'
  [ 1, 6 ]; "matched! >$(matched)<"
  else; 'zilch'
# returns "matched! >6<"

regular expressions

It's OK to match with regular expressions:

case 'ovomolzin'
  /a+/; 'ahahah'
  [ /u+/, /o+/ ]; 'ohohoh'   # <--- matches here
  else; 'else'

v.match and $(match)

When matching with a regular expression, the local variable 'matched' is set, as seen above, but also 'match':

case 'ovomolzin'
  /a+/; 'ahahah'
  [ /u+/, /^ovo(.+)$/ ]; "matched:$(match.1)"
  else; 'else'
# yields "matched:molzin"

defaulting to f.ret

When nothing is explicitly provided for consideration by "case", the incoming f.ret is used.

2
case
  [ 0 1 2 ]; 'low'
  6; 'high'
  else; 'over'
# yields 'low'

incoming f.ret is preserved

"case" makes sure f.ret gets to its upon-entering-"case" value when considered inside:

 7
 case (+ 3 4)
   5; 'cinq'
   [ f.ret ]; 'sept'
   6; 'six'
   else; 'whatever...'

 # yields 'sept'

"six"
case 6
  5; 'cinq'
  7; 'sept'
  6; "six $( f.ret | upcase _ )"
  else; 'je ne sais pas'

# yields "six SIX"

see also

Match, cond, if.

• source
• case spec