Cheat Sheet: Scheme (r7rs)

This is a cheat sheet, not a tutorial. It's meant to refresh your memory or help you find search terms for the docs, for those familiar with Scheme. Not all alternatives are macros. Not all macros are listed, only those that correspond to selected Scheme features.

Scheme Primitive	Alternatives
lambda	lambda
if	if-else, when
set!	set!, set@, define, my#.
include/include-ci	define on a fully qualified name.

Scheme Derived Conditional	Alternatives
cond	cond
case	case
and	ands
or	ors
when	when
unless	unless
cond-expand	.#(cond-, probably with information from sys. or os.

Scheme Derived Binding	Alternatives
let	let
let*	let*from. Maybe my#.
letrec/letrec*	my#. Possibly type.
let-values	let-from. (Python lacks multiple returns and conventionally returns a tuple instead.)
let*-values	let*from

Scheme Derived Iterating	Alternatives
do	any-map with range
named let	loop-from

Other Constructs	Alternatives
parameterize	defvar/binding, mk#patch
guard	engarde (prelude)
begin	progn
case-lambda	lambda with a case inside

Templates are pretty similar to Scheme's quasiquotation: `, ,, ,@. Beware that Lissp automatically qualifies symbols (like Clojure). We can still interpolate unqualified symbols though. $# does gensyms. Scheme's hygienic macros are not implemented, but we do have defmacro.

What looks like linked-list notation in Lissp makes tuples instead, so many linked-list operations are not applicable. (Tuples are more like vectors, but immutable.)

Python has no dedicated character type and instead uses length-1 strings.

Python doesn't have the tail recursion optimization. You can use loop-from/recur-from for direct recursion without using up the call stack. Python can do coroutines via two-way generators. We have Ensue (from the prelude) for that.

We don't have delay, force, or delay-force either. Python 3 uses lazy mutable iterators pervasively. They can be split with tee, but the results are still mutable iterators. ft#cache applied to an O# expression might be similar to a delay, which we can force by calling it. We needn't bother with the cache bit when the expression is pure (and fast).

Even for the R7RS-small base library, there are too many procedures to list for a cheat sheet. The hissp package bundles some metaprograms, but has no standard library of functions (or classes) and instead relies on Python's. For operator functions, see the operator module (these are all imported by the prelude. It also imports itertools.) /# makes a binary operator variadic via a reduce (E.g., (/#add 1 2 3) ; 6). For the rest, you need a Python reference.