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// Integrated test for content fields.
#let compute(equation, ..vars) = {
let vars = vars.named()
let f(elem) = {
let func = elem.func()
if func == text {
let text = elem.text
if regex("^\d+$") in text {
int(text)
} else if text in vars {
int(vars.at(text))
} else {
panic("unknown math variable: " + text)
}
} else if func == math.attach {
let value = f(elem.base)
if elem.has("t") {
value = calc.pow(value, f(elem.t))
}
value
} else if elem.has("children") {
elem
.children
.filter(v => v != [ ])
.split[+]
.map(xs => xs.fold(1, (prod, v) => prod * f(v)))
.fold(0, (sum, v) => sum + v)
}
}
let result = f(equation.body)
[With ]
vars
.pairs()
.map(p => $#p.first() = #p.last()$)
.join(", ", last: " and ")
[ we have:]
$ equation = result $
}
#compute($x y + y^2$, x: 2, y: 3)
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