Implicit vs Explicit Arguments

Question

Rewrite the following function using explicit named parameters instead of implicit x, y, z, then explain when you would choose each style.

f:{(x - y) % z}

Solution

pnlPct:{[entryPx; exitPx; notional]
  (exitPx - entryPx) % notional
 }

pnlPct[100.0; 105.0; 100.0]
/ 0.05

Explanation

The implicit form {(x - y) % z} works but gives the reader no hint about what the three arguments represent. Explicit names (entryPx, exitPx, notional) make the intent immediately clear. (Avoid names that are q keywords — exit, count, last, value and so on — as parameter or variable names.)

When to use implicit x, y, z:

• The function is very short (one expression) and the arguments are obvious from context
• Used inline as a lambda passed directly to an iterator

/ Clear enough as implicit
{x * x} each 1 2 3 4 5
(+/) each (1 2 3; 4 5 6)

When to use explicit names:

• The function body is more than one line
• The arguments have domain-specific meaning that a name communicates
• The function is called from multiple places in the codebase

/ Explicit names are worth it here
calculateVwap:{[price; qty]
  notional: sum price * qty;
  notional % sum qty
 }

One firm rule: never use x, y, or z as local variable names inside a function. They are reserved for arguments — reusing them as locals creates confusion about whether they still hold the original argument value at that point in the function.