// Map operation

// target function
inc(r)><(int i) => r~(i+1);
subPair(r)><(int m, int n) => r~(m-n);


// ----------- main (with the built-in Map and `%' notation) ----------- 
Map(r, %inc) ~ [1,2,3];
r;  // r ->[2,3,4]

Map(rr, %subPair) ~ [(10,2), (30,13)];
rr; // r4 ->[8,17]




// ----------- main (without the built-in Map) ----------- 
// map
map(result, f) >< []   => result~[], Eraser~f;
map(result, f) >< x:xs => Dup(f1,f2)~f, 
                          result~w:ws, 
                          f1 ~ (w, x), map(ws, f2)~xs;


// --- map application without the `%' notation ---
map(r1, (a, inc(a))) ~ [10,11,12];
r1; // r1 ->[11,12,13]

map(r2, (a, subPair(a))) ~ [(10,2), (30,13)];
r2; // r2 ->[8,17]


// --- map application with the `%' notation ---
map(r3, %inc) ~ [1,2,3];
r3;  // r3 ->[2,3,4]

map(r4, %subPair) ~ [(10,2), (30,13)];
r4; // r4 ->[8,17]