Broom

A programming language with first-class modules and algebraic effects. Still very much a work in progress (i.e. not yet usable).

(Planned) Features

• Functional-first, with strict evaluation
• ML-style module system with higher-order, recursive and first-class modules
  • Records and modules are the same, à la 1ML
  • First-class ML-modules also provide higher-ranked and higher kinded types
    • with impredicative instantiation
  • Modular implicits support ad-hoc polymorphism and type level programming
• Algebraic effects and effect handlers
• Row typed modules, records, polymorphic variants and effects
• Conventional and simplified syntax
  • extensible with procedural hygienic macros
• Optimizing whole-program compilation to Javascript or (later) native code

(Abstract) Syntax

program ::= defs
repl_input ::= stmts

stmt ::= def | expr
stmts ::= (stmt (";" stmt)*)? ";"?
alts ::= (stmt ("|" stmt)*)? "|"?

def ::= pat "=" expr
defs ::= (def (";" def)*)? ";"?

exprs ::= types ::= (expr ("," expr)*)? ","?

expr ::=
pat ::=
type ::= 
    | type ("-!" type)? "->" type
    | type "=>" type

    | expr ":" type
    | expr "||" expr
    | expr "&&" expr
    | expr ("==" | "<" | "<=" | ">" | ">=") expr
    | expr ("+" | "-") expr
    | expr ("*" | "/") expr
    | expr OTHER_INFIX expr
    | expr expr+
    | PREFIX expr
    | expr POSTFIX
    | expr "." ID

    | "{" ("|" pat ("," pat)* "->" expr)+ "}" (* function literal *)
    | "{" "|" "->" stmts "}" (* thunk *)
    | "{" "|" "}" (* empty function (uncallable) *)
    | "{" ("|" pat ("," pat)* "=>" expr)+ "}" (* implicit function literal *)
    | "{" stmts "}"
    | "[" exprs "]"
    | "(" exprs ")"
    | "(" ( "||" | "&&"
          | "==" | "<" | "<=" | ">" | ">="
          | "+" | "-"
          | "*" | "/" | "%" ) ")"
    | "{" ":" stmts ")"
    | "[" "|" alts "]"
    | "(" "|" alts ")"
    | "(" ":" types ")"

    | ID
    | "_"
    | CONST

See the intro for a slightly more detailed exposition.