Conditions

if (#score > 10) {
    /say big;
} else if (#score > 5) {
    /say medium;
} else {
    /say small;
}

A condition works like execute if in Minecraft:

Condition	Compiles to
#a > 5, #a == #b	if score ...
@s.$SelectedItem.components.enchantments	if data entity @s SelectedItem.components.enchantments, which tests that the path exists
!$stats.bonus	unless data storage <ns>:data stats.bonus
@s.$OnGround == true	if data entity @s {OnGround:1b}
$name == "Steve"	if data storage <ns>:data {name:"Steve"}
$ratio == 5f	if data storage <ns>:data {ratio:5f}
block ~ ~-1 ~ #minecraft:logs	if block ~ ~-1 ~ #minecraft:logs
items entity @s weapon.mainhand #self:swords	if items entity @s weapon.mainhand #<ns>:swords
!entity @s[type=#minecraft:undead]	unless entity @s[type=#minecraft:undead]
predicate self:isSitting	if predicate <ns>:is_sitting

Combine conditions with and, or and !.

A condition can also be an execute if check, written as you would write it in a command:

if (block ~ ~-1 ~ #minecraft:logs) { /say on a log; }

Poplar treats a condition as a check when it starts with one of these words and a space: biome, block, blocks, data, dimension, entity, function, items, loaded, predicate, score, slots or stopwatch. The check ends at and, or or the closing ).

Checks work like the text of a command. The compiler checks them against the command tree, you can name something in your pack with self:name, and {{...}} inserts a constant or a $(name) macro argument:

namespace demo;

itemTag swords { "values": ["#minecraft:swords"] }

var #mana = 0;

mcfun tick() {
    if (block ~ ~-1 ~ #minecraft:logs and #mana > 5) {
        /say on a log;
    } else if (items entity @s weapon.mainhand #self:swords) {
        /say sword;
    }
}

# tick
execute if block ~ ~-1 ~ #minecraft:logs if score #global demo.mana matches 6.. run return run say on a log
execute if items entity @s weapon.mainhand #demo:swords run return run say sword

A bare data path tests that the path exists, whatever its value. A bool always exists (0b or 1b), so compare it with == true or == false. Comparing data with a string, bool, list, compound or typed number (5f) is an NBT match; comparing it with a plain int reads it into a score.

The compiler decides a condition that has only constants, and it writes only the branch that is taken.

A body with one command goes inline after run. A longer body becomes its own function, poplar/<mcfun>/if_<n>. Inside a runtime if, you can’t change a constant declared outside it.

Costs and caveats

• A body with more than one command is a function call.
• else, else if and or use one wrapper function.
• A Minecraft check is raw text, so tags and ids in other namespaces aren’t checked. The word and or or ends the check unless it is inside brackets or quotes.
• A game value in a Minecraft check is an error, for {{#x}} and {{$x}} alike. Use execute (if ...) { } instead.
• == with data only works on key paths. $stats.name == "x" works, and $list[0] == "x" is an error. You can’t compare two game values that aren’t numbers.