x+2..=42 (expression start, 39 iterations summing 897),
x+2<..<x*21 (expressions both ends, 5..41), 0..x*3 (expression end).
Expression parsing stops at the range lexeme from either side, so any
expression works in either position — now pinned.
Each side of '..' takes an optional bound marker, defaulting to
start-inclusive, end-exclusive (a..b == a=..<b; a..=b stays the short
end-inclusive spelling):
for 0<..<N (i) { } // 1 .. N-1 (both exclusive)
for 0=..=N (i) { } // 0 .. N (both inclusive)
for 0<..=N (i) { } // 1 .. N
for 0..<N (i) { } // 0 .. N-1 (explicit default)
for xs, 2<.. (x, i) // open range, exclusive start: i = 3, 4, ...
The nine lexemes are single tokens (maximal munch on '<'/'='/'..'), so
expression parsing never sees the leading marker as a comparison; '<',
'<<', '<=', '==', '=>' lex unchanged. An explicit end marker makes the
end expression mandatory; open forms are a.. / a<.. / a=... Works in
runtime, multi-iterable, and inline-for headers.
Regression: examples/0051-basic-for-range-bounds.sx (full matrix, open
start-marked ranges, comptime unroll, runtime bounds, lexer
non-regression); 1152's pinned message generalized.
