Disclaimer: this is probably just a nitpick. On guile-user someone brought up that (lambda () (begin)) errors, arguably counter-intuitively:
http://lists.gnu.org/archive/html/guile-user/2014-07/msg00005.html After much investigation over this trivial matter, I found that while it's compliant with the RnRS (it's unspecified), it means Guile extends the RnRS grammar in an "unexpected" way. According to R5 and 7RS: <lambda expression> -> (lambda <formals> <body>) <body> -> <definition>* <sequence> <sequence> -> <command>* <expression> <expression> -> (other stuff) | <derived expression> <derived expression> -> (other stuff) | (begin <sequence>) meaning that the "(begin)" in that lambda body can be matched up to <derived expression>, where it then almost matches the `begin' form but fails only because in the RnRS grammar it must have at least one expression (see <sequence> again; this is also reflected in section 4.2.3 where this `begin' form is explained; its template clearly shows it must have at least one expression operand). Guile on the other hand *generally* allows the expression-begin to have zero operands, having it return *unspecified*. So one would expect it to work here as well, since one expects that this is a small incremental extension to the RnRS grammar, but that's not the case. If I'm not mistaken, `expand-body' in psyntax would be the place to tackle this, and from a quick glance I'm guessing the benefit/effort ratio for changing this is not very high. :-) Taylan
