Cookbook — everyday programs

The classic first programs, written the idiomatic Sutra way. Every snippet on this page compiles, runs on the substrate, and produces exactly the output shown.

Two conventions to know up front:

• Truth is signed. (number) on a condition gives +1 (true) / −1 (false) / 0 (unknown) — the Kleene scale. A 0/1 counter maps via ((number) cond + 1) / 2.
• Sharpen select with gain. select is a softmax blend; multiply scores by ~10 when you want a near-hard choice.

Sum an array

foreach_loop total(arr, int acc) { pass acc + element; }

function int main() { return loop total([3, 1, 4, 1, 5], 0); }   // 14

Max of an array

foreach_loop maxi(arr, int best) {
    int e = element;
    number s = 10 * (number)(e > best);
    pass select([s, 0 - s], [e, best]);
}

function int main() { return loop maxi([3, 1, 4, 1, 5], 0); }    // 5

No if — the winner is a gain-sharpened select between the candidate and the incumbent.

Count matches

while_loop count(i < 3, int n, String s, int i) {
    pass n + ((number)(string_char_at(s, i) == 97) + 1) / 2, replace, i + 1;
}

function int main() {
    (n, s2, i) = loop count((0 < 3), 0, make_string("aba"), 0);
    return n;                                                    // 2
}

string_char_at returns the codepoint (97 = 'a'); the (±1 + 1) / 2 maps signed truth onto a 0/1 increment.

Reverse a string

while_loop rev(i > 0, String out, String s, int i) {
    pass string_concat(out, make_char(string_char_at(s, i - 1))), replace, i - 1;
}

function string main() {
    (out, s2, i) = loop rev((3 > 0), make_string(""), make_string("abc"), 3);
    return out;                                                  // "cba"
}

make_char lifts a codepoint back into a 1-character String for concatenation. replace keeps s at its call-time value each tick.

Fibonacci

iterative_loop fib(8, int a, int b) {
    pass b, a + b;
}

function int main() {
    (a, b) = loop fib(8, 1, 1);
    return a;                                                    // 34
}

Multi-value pass assigns in parallel — a + b reads the pre-tick a, exactly like a simultaneous recurrence.

Palindrome check

while_loop pal(i < 3, fuzzy ok, String s, int i) {
    pass ok && (string_char_at(s, i) == string_char_at(s, 3 - 1 - i)), replace, i + 1;
}

function int main() {
    (ok, s2, i) = loop pal((0 < 3), true, make_string("aba"), 0);
    return (number) ok;                          // "aba" → 1;  "abc" → ≈ −1
}

Find a character (index-of)

while_loop find((i < 3) && (string_char_at(s, i) != 98), int i, String s) {
    pass i + 1, replace;
}

function int main() {
    (i, s2) = loop find((0 < 3), 0, make_string("aba"));
    return i;                                                    // 1  ('b' = 98)
}

The compound halt (&& of a bound and a character test) runs on the substrate like everything else.

Parameterize an iteration count

Loop functions have no outer-scope access — thread a caller’s value as a state parameter:

while_loop tri(i <= n, int acc, int i, int n) {
    pass acc + i, i + 1, replace;
}

function int triangular(int k) {
    (acc, i, n) = loop tri((1 <= 1), 0, 1, k);
    return acc;
}

foreach_loop total(arr, int sum) {
    int e = element;
    pass sum + triangular(e);
}

function int main() { return loop total([1, 2, 3], 0); }         // 10

Loops calling functions calling loops compose freely.

FizzBuzz

The classic lives in the demos: FizzBuzz on the demos page — a softmax select superposition picks each word, and a loop threads the growing String accumulator.

For the loop surface itself (all three call forms), see Loops.