Control Flow

Structural directives (if, each) wrap Markdown body text between hyogen comment blocks. Imperative loops run entirely inside @hg blocks.

if / else / endif

Pug-style — open with a hyogen block, write Markdown, close with another block:

<!--
@hg
const isNight = true
@endhg
-->

<!--
@hg
if isNight
@endhg
-->
I can see the full moon.
<!--
@hg
else
@endhg
-->
I can see the shiny sun.
<!--
@hg
endif
@endhg
-->

Conditions use the same expression rules as {{ }}. Truthy / falsy follows JavaScript.

else if

<!--
@hg
if score >= 90
@endhg
-->
Grade A.
<!--
@hg
else if score >= 60
@endhg
-->
Grade B.
<!--
@hg
else
@endhg
-->
Grade C.
<!--
@hg
endif
@endhg
-->

Empty branches (no body) are allowed. Unmatched if or extra endif causes parse_error.

each / endeach

Loop over arrays or iterable-like values. Body is Markdown between blocks:

<!--
@hg
const fruits = ["apple", "banana", "orange"]
@endhg
-->

<!--
@hg
each item in fruits
@endhg
-->
- {{ item }}
<!--
@hg
endeach
@endhg
-->

Object arrays:

<!--
@hg
each item in data
@endhg
-->

- {{ item.key }} is {{ item.value }}

<!--
@hg
endeach
@endhg
-->

Loop variables and parent scope are both visible inside the body.

Nesting limit

if and each structural nesting is limited to 20 levels combined. Exceeding the limit skips the block and emits nest_limit_exceeded.

Nested if inside each (and vice versa) is allowed within the limit.

C-style for and do…while

These run entirely inside @hg blocks (no Markdown body between markers):

<!--
@hg
for (let i = 0; i < 3; i++) {
  // imperative logic only
}
@endhg
-->

while alone, for…of, and for…in are not allowed.

Ternary in expressions

For simple branching in text, prefer ternary inside {{ }}:

{{ isNight ? "Dark" : "Light" }}

See Expressions.