1 Examples🔗ℹ

Here are some example shrubberies. Each line either uses old indentation to continue a nesting level that was started on a previous line, starts with new indentation and follows a line that ends with :, or starts with new indentation and a | on the same line. A : or | can also appear in the middle of a line, but that’s roughly a shorthand for starting a new indented line after the : or before the |. The complete rules involve more terminology, but that’s enough to get a sense of the examples.

fun identity(x): x

fun fib(n):

match n

| 0: 0

| 1: 1

| n: fib(n-1) + fib(n-2)

fun print_sexp(v):

match v

| []: print("()")

| [fst, & rst]:

print("(")

print_sexp(fst)

for (v: rst):

print(" ")

print_sexp(v)

print(")")

| Pair(fst, snd):

print("(")

print_sexp(fst)

print(" . ")

print_sexp(snd)

print(")")

| v: print_atom(v)

Forms like fun, match, and for are not specified by shrubbery notation, since specifying those forms is up to a language that is built on top of shrubbery notation. Still, shrubbery notation is meant to accommodate a particular kind of syntax for nested blocks (via : and indentation) and conditional blocks (via |).

Identifiers are C-style with alphanumerics and underscores. Operators are sequences of symbolic characters in the sense of char-symbolic?, roughly. No spaces are needed between operators and non-operators, so 1+2 and 1 + 2 mean the same thing. Comments are C-style. See Token Parsing for more information.

The following tokens are used for grouping, in addition to line breaks and indentation:

Parentheses, square brackets, and curly braces are used to delimit groups in the obvious way. A ' is used in a parenthesis-like way, too, and it’s intended for quoting shrubbery terms. A ; or , acts as a group separator, even within a single line. A : or | treats remaining item on the same line like a new indented line, which forms a block of nested groups. A guillemet pair « and » can be used in rare cases to explicitly bracket subgroups formed by : and | without line breaks. A \ continues a line, effectively shifting all columns on the next line as if they appeared immediately after the \.