ocaml — consolidated language guide — DedSec Project

OCaml

How the language behaves

OCaml combines algebraic data types and pattern matching with modules, and supports both functional and imperative programming.

Source fragment to analyze

let rec length = function
  | [] -> 0
  | _ :: xs -> 1 + length xs;;

Deliberate exercise

Trace the recursion over an empty and a three-element list, and read the compiler warning when a new match is incomplete.

Check a failure condition

An exception or missing match case is not fixed by unsafe wildcard swallowing; enumerate intended constructors.

Record input, expected output and observed output with the actual OCaml implementation and version. If no compatible runtime exists on your current platform, label the fragment unexecuted and reason from its semantics rather than claiming a successful run. Run a second isolated experiment that changes only the mechanism under investigation; preserve the exact diagnostic while removing private data.

OCaml — Expanded practice workbook

Make the zero-denominator contract explicit

OCaml integers are not unbounded and integer division must not silently fail on zero. Create safe_div.ml:

let safe_div a b =
  if b = 0 then None else Some (a / b)

let () =
  assert (safe_div 9 2 = Some 4);
  assert (safe_div 9 0 = None);
  assert (safe_div (-7) 2 = Some (-3));
  print_endline "checks passed"

Run using ocaml safe_div.ml or compile with an installed OCaml compiler. In OCaml, integer division truncates toward zero, hence -7 / 2 produces -3. Compare this with mathematical floor division; a language-independent phrase like "round down" would be incorrect here. Do not treat None as the number zero.

Trace pattern matching

Write a formatter: let show = function None -> "invalid" | Some n -> string_of_int n. This pattern covers both constructors. Deliberately omit the None arm and inspect the compiler's non-exhaustive-match warning. A warning is not guaranteed to be a hard compilation failure unless warning settings request it. Explain what input could then trigger Match_failure.

Side effects versus values

The let () = block performs assertions and printing; safe_div itself only computes an option value. Distinguish this from an exception-raising divider: callers can inspect the optional result without catching an exception. Make the function accept a pair and apply it to multiple fixtures, preserving each input so failures can be explained.

Further investigation

Check max_int and min_int and explain why fixed-width int cannot be assumed to represent arbitrary mathematical integers. Add negative divisors, numerator zero and an empty list of requests. Document whether each behavior was tested in interpreter or inferred from code; do not invent runtime evidence. Reference: https://ocaml.org/docs