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Destination Calculus:

A Linear 𝜆-Calculus for Purely Functional Memory Writes

Topics in Compiler and Concurrency

Julius Fischer

10. Juni 2026

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What are Destinations?

• Destination Passing Style
  • Imperative
  • Function takes destination instead of returning structure

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Example in C

int* vec_add(int v1[], int v2[], int size) {
    int* res =  malloc(size * sizeof(int));
    for (int i = 0; i < size; i++) {
        res[i] = v1[i] + v2[i];
    }
    return res;
}

• Add an 'out parameter'

void dps_vec_add(int res[], int v1[], int v2[], int size) {
    for (int i = 0; i < size; i++) {
        res[i] = v1[i] + v2[i];
    }
}

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Motivation for DPS

• Typical functional map implementation

map f (x:xs) = (f x : map f xs1)
> (f x : map f xs) 
> (map f x1 : (f x2 : map f xs2)) 
> ...

• Not tail recursive
  • Performance issue
  • Inefficient stack growth

map f (x:xs) dest = map f xs (push dest (f x))
> map f xs1 (push dest (f x1))
> map f xs2 (push dest (f x2))

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DPS in functional languages

• Just add pointers to mutable data?
  • Int \mapsto Int \mapsto Int \mapsto \textcolor{red}{T}
  • \textcolor{red}{T *}\mapsto Int \mapsto Int \mapsto Int \mapsto Void

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Destination Calculus

• It's

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Referenes