Reuse & logic

#Constants

@let declares named constants, spliced as text with {{name}} wherever they are used — prose, attribute values, code bodies. The attribute group is the bindings, so @let has no attributes of its own and no head shorthand (@let:x is an error).

@let(source-note: Johnson & Raven (1973))

As reported in {{source-note}}.

#Conditionals

@if compiles its body only when every condition holds. Conditions test @let constants by exact value, the group is the conditions, and naming an undeclared constant is a compile error:

@let(audience: teacher)

@if(audience: teacher){
    note{
        Answers are collected in the closing scene.
    }
}

#Repetition

@for repeats its body. The implicit attribute n is a non-negative count (@for:3) or an inclusive ascending range (@for:0..6), and {{i}} splices the counter:

@for:0..4{
    point(x: {{i}}; y: {{i}})
}

as: renames the counter — as: k makes the splice {{k}} — which is how nested loops tell their counters apart:

@for(n: 0..2; as: row){
    @for(n: 0..2; as: col){
        point(x: {{row}}; y: {{col}})
    }
}

#Templates

@define declares a template — a node shape written once and stamped out wherever its name is used. The head names the type (@define:swatch — the implicit attribute is node), the group declares the template's parameters with their defaults, and {{param}} splices each one verbatim into the body:

@define:swatch{
    square(x: 0; y: 0; size: 1; colour: {{colour}})
}(
    colour: blue
)

swatch(colour: red)

#Presets

@preset bundles attributes for reuse. Three forms: @preset:text(size: 24) is anonymous and applies to every text node; @preset#accent(...) is named and applied by hand with preset: #accent; @preset#accent:text(...) is both named and scoped to one type. Presets apply to block nodes only, must be declared before use, cannot reference other presets, and share the one document-wide #id namespace.

#Includes

@include splices a partial — a .part.chalk attachment — into the document at compile time, exactly where the directive is written: @include:overview.part.chalk. A dataset or constant declared in an included file is visible to the whole document, and circular includes are a compile error.

#Comments

@ignore is the block comment: its body is discarded before parsing — drafts, notes to self, content taken out of circulation without deleting it. Braces inside still need to balance; it takes no attributes and no implicit value.