The problem is that unix pipe can be blocked and you can see it as a lazy partial evaluation, so grep a HUGEFILE|head returns when 10 lines are found. In APL t

The problem is that unix pipe can be blocked and you can see it as a lazy partial evaluation, so grep a HUGEFILE|head returns when 10 lines are found. In APL the semantics is not builtin, though things like ⍴↑↓ can be lazy, it's the internal optimization, rather than a language specification.