giles
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Side-quests required to land caesar.ml:
1. Top-level 'let r = expr in body' is now an expression decl, not a
broken decl-let. ocaml-parse-program's dispatch now checks
has-matching-in? at every top-level let; if matched, slices via
skip-let-rhs-boundary (which already opens depth on a leading let
with matching in) and ocaml-parse on the slice, wrapping as :expr.
2. runtime.sx: added String.make / String.init / String.map. Used by
caesar.ml's encode = String.init n (fun i -> shift_char s.[i] k).
3. baseline run.sh per-program timeout 240->480s (system load on the
shared host frequently exceeds 240s for large baselines).
caesar.ml exercises:
* the new top-level let-in expression dispatch
* s.[i] string indexing
* Char.code / Char.chr round-trip math
* String.init with a closure that captures k
Test value: Char.code r.[0] + Char.code r.[4] after ROT13(ROT13('hello')) = 104 + 111 = 215.
15 lines
432 B
OCaml
15 lines
432 B
OCaml
let shift_char c k =
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let n = Char.code c in
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if n >= 97 && n <= 122 then
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Char.chr (((n - 97 + k) mod 26 + 26) mod 26 + 97)
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else c
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let encode s k =
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String.init (String.length s) (fun i -> shift_char s.[i] k)
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;;
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(* ROT13 round-trip: encode (encode "hello" 13) 13 = "hello".
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Sum the codes of two chars to give a deterministic integer check. *)
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let r = encode (encode "hello" 13) 13 in
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Char.code r.[0] + Char.code r.[4]
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