Updating Nu

Goals

Useful existing features of Nu:

• S-expression grammar.
• Macros and special-purpose operators (e.g. Markup generation)
• Built-in code formatting.
• Easy integration with C code using an Objective-C runtime.

Interesting new features:

• Explicit support for Protocol Buffer serialization and deserialization.
• Protocol Buffer representation of parsed code and program state.
• Packages for high-level code organization.
• Data structures represented as messages. Composition used instead of inheritance.
• Methods as functions bound to messages.
• Dot notation for concise access to package and message members.
• Keyword arguments for functions and methods.
• Freezable state for transporting running programs between servers.

Operators

Code structure

operator	description
package	Declare a package. A package can contain messages, services, and functions.
message	Declare a message. A message is a collection of fields and optional functions.
service	Declare a service. A service is a collection of rpcs.
rpc	Declare a remote procedure call.
func	Define a function. Functions can be anonymous or named and optionally associated with messages.
set	Create a variable and set it or modify an existing variable.
car cdr cons	Every Lisp needs these basic list manipulation operators.

Built-in types

All of these (except character and error) can be used in a message declaration to declare a field. All can be used as operators to “cast” a value to the associated type or return nil if the value is not representable with that type.

operator	description
map	Associative map.
array	Array (repeated field).
error	Get an error from a value or return nil if there is no error.
double float	Floating-point types
int32 int64 uint32 uint64 sint32 sint64 fixed32 fixed64 sfixed32 sfixed64	Integer types
bool	Boolean
string	A string must always contain UTF-8 encoded or 7-bit ASCII text.
bytes	May contain any arbitrary sequence of bytes.
character	UTF-8 code point. May not be used in messages (use int32 instead).
enum	32-bit integer
oneof	Groups fields so that at most one can be set.

Concurrency

operator	description
go	Start a concurrent process
condition.new	Create a condition variable

Control flow

operator	description
if then else
cond else
while

Evaluation

operator	description
quote	Quote an expression.
eval	Evaluate an expression.
defer	Evaluate an expression at the end of the current block, implicitly quoting the expression.

Arithmetic

operator	description
+ - * /
eq ne

Input/Output

operator	description
puts
reads
putf
readf

Protocol Buffer integration

Messages can be declared with expressions, stored to variables, and used to call protoc plugins.

File descriptor sets can be read and parsed into package descriptions, and then displayed as expressions.