if

if and unless return a value only when their condition is true.

When used as expressions, these are ? values.

These parse specially; if a block is present, it always goes with the if, even if there's another keyword in between.

. if true 0
. if (or true false) 1
|| Thanks to special parsing, this is `unless (not true) 2`, not `unless (not true 2)`.
. unless not true
	2
. unless and true false
	3

There is no else expression to go with if; use cond or case (both below) instead.

cond

For simple conditionals, use cond. This is like JavaScript's ternary operator.

Like anything else, the "else" value can go in a block. What if you want blocks for both "then" and "else"? Use case.

. cond true 'then 'else
. cond false 'then
	'else

switch

This is just like JavaScript's.

You don't need to break explicitly. Fallthrough is not supported.

To handle multiple cases the same way, just write multiple values on one line.

else handles anything not covered by another case.

f = \n
	switch n
		0
			"zero"
		1 2
			"a small number"
		else
			"some other number"
. f 0
. f 1
. f 2
. f 3

If there is no else, an error will be thrown for an unhandled case.

(If you really want to do nothing, just write pass in the else block.)

focus

The focus, _, is a good short-lived variable when you don't need a name.

There's some helpful syntax for using it:

Many expressions implicitly assign to the focus.
fun_ is short for (fun _).
:Type is short for _:Type. (See types)

case

case is Mason's replacement JS's if ... else if ... else.

Tests are tried from top to bottom until one matches.

Tests are each written on their own line, with the result for that test in a block next to it.

Just like switch, a missing else will throw an error.

An expression written on the same line as case on the same line will become the focus. This is optional but recommended.

rate-guess = \guess
	case guess
		|| implicitly, `_ = guess`
		<? _ 7
			"Too low!"
		>? _ 7
			"Too high!"
		else
			"You got it!"

. rate-guess 6
. rate-guess 8
. rate-guess 7

\case and \switch create functions with a single implicit argument: _.

rate-guess = \case
	=? _ 7
		"You got it!"
	else
		"Off by #(- _ 7)"

. rate-guess 1337

rate-guess-2 = \switch
	7
		"You got it!"

. rate-guess-2 7