6.5. LINQ fold macros (_fold / _old_fold)

The LINQ_FOLD module provides the _fold and _old_fold call macros that rewrite LINQ pipelines into optimized loop forms — _fold is the active fusion macro, _old_fold is a frozen pre-rewrite baseline kept for benchmark comparison as _fold evolves toward splice-mode fusion.

The dispatch infrastructure (linqCalls table, fold_* helpers, fold_linq_default) is private to this module; only the two macros are user-facing. daslib/linq_boost re-exports them via require daslib/linq_fold public so existing call sites that require daslib/linq_boost continue to resolve _fold(...) without change.

See also LINQ for the underlying query operations and Boost module for LINQ for the surrounding macro family.

All functions and symbols are in “linq_fold” module, use require to get access to it.

require daslib/linq_fold

Example:

require daslib/linq
require daslib/linq_boost

[export]
def main() {
    let arr = [1, 2, 3, 4, 5]
    let n = _fold(each(arr)._where(_ > 2).count())
    print("{n}\n")
}
// output:
// 3

6.5.1. Call macros

_old_fold

Frozen pre-rewrite baseline of _fold. Same expansion as _fold today; the two diverge only when later PRs add splice-mode fusion to _fold. Benchmarks compare _fold vs _old_fold to track performance work — _old_fold must keep producing the historical shape so the comparison stays meaningful. for example:

_old_fold(each(foo)._where(_ > 5)._select(_ * 2))

_fold

implements _fold(expression) that folds LINQ expressions into optimized sequnences for example:

_fold(each(foo)._where(_ > 5)._select(_ * 2))

expands into a single comprehension that does all operations in one pass