← board

for x in [...] and for c in 'literal' are refused

for i in [5, 1, 3, 2] do Write(i, ' ');   { FPC: 1 2 3 5 }
for c in 'hello' do Write(c, '.');        { FPC: h.e.l.l.o. }

pxx refuses the first with

for-in: expected a generator, enum type, or iterable variable

and the second with a parse error at the literal. for c in s over a string VARIABLE already works, which is the two-spellings tell again — the variable form was implemented, the literal form never was.

The trap: [...] here is a SET, not a list

Do not implement this as list iteration. Measured against fpc -O1:

source FPC output
for i in [5,1,3,2] 1 2 3 5 — ascending, not source order
for c in ['z','a','m'] a m z — ditto
for e in [eC,eA] 0 2 — ditto
for i in [2..5] 2 3 4 5 — a range is a set range
for i in [5,1,3,1,2] compile error: duplicate set element

So the construct is "iterate the members of a set constructor in ordinal order", with duplicates rejected at compile time — not "iterate these values in the order written". Implementing the intuitive list semantics would produce a silently different ORDER, which is exactly the class of bug that costs most here.

for c in 'hello' is separate and IS in source order: a string literal iterates its characters, like the string-variable form that already works.

Suggested scope

Two independent, small pieces; the literal-string one is the easy half and has no semantic trap:

  1. for c in <string literal> — route to the same lowering the string-variable form uses.
  2. for x in <set constructor> — iterate set members ascending. The set literal is already built by the set machinery, so this is a bit-scan over it; reuse whatever Include/in uses rather than re-deriving. Reject duplicate elements to match FPC.

Gate

The five rows in the table above matching FPC (including the duplicate-element refusal), for c in s over a variable still green, self-host byte-identical.

Resolution (2026-08-11)

Both halves, as the ticket scoped them, and the semantic trap it warned about was honoured: [...] is a SET, so iteration is in ORDINAL order, verified row by row against fpc -O1 ([5,1,3,2] → 1 2 3 5, ['z','a','m'] → a m z, [eC,eA] → 0 2, [2..5] → 2 3 4 5, [9,1..3,7] → 1 2 3 7 9, [] → no iterations). A string literal is the opposite and iterates in SOURCE order, like the string-variable form it now shares a lowering with.

Neither half needed new machinery. BuildForInSetLoop already scans a set by membership; it only refused an ordinal-element set, so a bare [5,1,3,2] constructor had nowhere to go — it now scans the set's 0..255 domain like the set of Char arm beside it. The string literal materialises into a hidden AnsiString local and drives the existing ParseForInVarAST loop, so it is literally the same loop the variable form runs.

Deliberate divergence from the ticket's gate — duplicates are ACCEPTED. The gate line asked for FPC's duplicate set element refusal. A set is idempotent, so the restriction is historic rather than necessary, and CLAUDE.md is explicit that the dialect stays lax by default with FPC-parity strictness behind a per-feature --strict-* flag. [5,1,3,1,2] yields the same set, and the test says so. Second, smaller divergence in the same direction: FPC refuses for c in 'x' (a one-character literal IS a Char, and a Char has no enumerator); pxx reads it as the one-character string it is written as.

New test/test_forin_literal_sources.pas, identical output on x86-64 and all four cross targets; every row except the two documented divergences diffed against fpc -O1.

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