Jensen's Device: Difference between revisions
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Line 505:
print harmonic_sum(i, 1, 100, lambda: 1.0/i.value)</lang>
Output: 5.18737751764
=={{header|R}}==
R uses a [http://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_need call by need] evaluation strategy where function inputs
are lazily evaluated and then cached; functions can implement
nonstandard evaluation such as call-by-name by using the "substitute" primitive to
access the parse tree of the unevaluated input. There are some proposed
[http://developer.r-project.org/nonstandard-eval.pdf conventions] to do this in a way that is less confusing to the user
of a function. The following ignores any conventions to mimic the effect
of the original ALGOL where "i" is truly assigned in the calling context.
<lang R>
sum <- function(var, lo, hi, term) {
s <- 0
for (i in lo:hi) {
eval.parent(substitute(x <- i, list(x=substitute(var), i=i)))
s <- s + eval.parent(substitute(term))
}
s
}
print(sum(i, 1, 100, 1/i))
</lang>
=={{header|Ruby}}==
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