@top Script { terminator* line+ }

@skip { space | comment }

line { (expression | toplevel) terminator+ }

toplevel { Import | Use | Ns }

Import { skw<"import"> String skw<"as"> Word }

Use { skw<"use"> Word }

Ns {
	skw<"ns"> Word "{"
	separator*
	assoc_term (separator+ assoc_term)*
	separator*
	"}"
}

expression { non_binding | binding }

binding { Let | Ref | Fn_Named | Fn_Compound }

Ref { skw<"ref"> Word "=" expression }

non_binding { simple | complex }

synth_root { Word | Keyword }

synth_term { Args | Keyword }

arg_term { Placeholder | simple }

Args {
	("(" separator* ")")
	| ("("
	separator*
	arg_term (separator+ arg_term)*
	separator*
	")")
}

Synthetic { synth_root synth_term+ }

complex {
	Block
	| If
	| If_Let
	| Match
	| When
	//| Do
	//| Bind
	| Loop
	| Repeat
	| Each
}

Repeat { skw<"repeat"> (Word | Number) Block }

Each { skw<"each"> simple "do" (Fn_Clause | Fn_Clauses) }

Recur { skw<"recur"> Args }

Loop { skw<"loop"> simple "with" (Fn_Clause | Fn_Clauses) }

simple { atom | collection | Synthetic | Fn_Lambda | Recur }

Fn_Clause { Tuple_Pattern "->" non_binding }

Fn_Clauses { 
	"{"
	terminator*
	Fn_Clause (terminator+ Fn_Clause)*
	terminator*
	"}"
}

Fn_Compound { skw<"fn"> Word Fn_Clauses }

Fn_Named { skw<"fn"> Word Fn_Clause }

Fn_Lambda { skw<"fn"> Fn_Clause }

// TODO: figure out precedence with do/bind exprs
// do_expr { Fn_Lambda | Synthetic | Word | Keyword }

// Do {
// 	skw<"do"> simple (~ambig newline* ">" do_expr)+
// }

// Bind {
// 	skw<"bind">
// 	simple
// 	(!pipeline pipeline)+
// }

Pattern {
	Tuple_Pattern
	| List_Pattern
	| Dict_Pattern
	| Struct_Pattern
	| atom
	| Placeholder
}

Placeholder { "_" }

ellipsis { "..." }

Splattern { ellipsis (Word | Placeholder) }

Tuple_Pattern {
	("(" separator* ")")
	| ("("
	separator*
	(Pattern separator+)* (Pattern | Splattern)
	separator*
	")")
}

List_Pattern {
	("[" separator* "]")
	| ("["
	separator*
	(Pattern separator+)* (Pattern | Splattern)
	separator*
	"]")
}

Assoc_Pattern { Word | (Keyword Pattern) }

Dict_Pattern {
	("#{" separator* "}")
	| ("#{"
	separator*
	(Assoc_Pattern separator+)* (Assoc_Pattern | Splattern)
	separator*
	"}")
}

Struct_Pattern {
	("@{" separator* "}")
	| ("@{"
	separator*
	(Assoc_Pattern separator+)* (Assoc_Pattern | Splattern)
	separator*
	"}")
}

Let { skw<"let"> Pattern "=" non_binding }

Else { skw<"else"> }

Match_Clause {(Pattern | Else) "->" newline* expression}

match_body {
	Match_Clause
	| (
		"{"
		terminator*
		Match_Clause (terminator+ Match_Clause)*
		terminator*
		"}"
	)
}

Match {
	skw<"match">
	simple
	skw<"with">
	match_body
}

When_Clause {
	(simple | Placeholder | Else) "->" newline* expression
}

When {
	skw<"when"> "{"
	terminator*
	When_Clause (terminator+ When_Clause)*
	terminator*
	"}"
}

If {
	skw<"if"> simple newline*
	skw<"then"> expression newline*
	skw<"else"> expression
}

If_Let {
	skw<"if"> skw<"let">
	Pattern "=" simple newline*
	skw<"then"> expression newline*
	skw<"else"> expression
}

Block {
	"{"
	terminator*
	expression (terminator+ expression)*
	terminator*
	"}"
}

collection {
	Tuple
	| List
	| Set
	| Dict
	| Struct
}

Tuple {
	( "(" // non-empty
		separator*
		non_binding (separator+ non_binding)*
		separator*
		")" )
	| "(" separator* ")" // empty
}

Splat { ellipsis Word }

linear_term { Splat | non_binding }

List {
	("["
		separator*
		linear_term (separator+ linear_term)*
		separator*
		"]" )
	| "[" separator* "]"
}

Set {
	("${"
	separator*
	linear_term (separator+ linear_term)*
	separator*
	"}")
	| "${" separator* "}"
}

assoc_term { Word | (Keyword non_binding) }

dict_term { assoc_term | Splat }

Dict {
	("#{"
		separator*
		dict_term (separator+ dict_term)*
		separator*
		"}" ) 
	| "#{" separator* "}"
}

Struct {
	("@{"
		separator*
		assoc_term (separator+ assoc_term)*
		separator*
		"}")
	| "@{" separator* "}"
}

atom { Boolean | Nil | String | Number | Keyword | Word }

kw<term> { @specialize[@name={term}]<Word, term> }

skw<term> { @specialize<Word, term> }

Keyword { ":" Word }

Boolean { kw<"true"> | kw<"false"> }

Nil { skw<"nil"> }

@tokens {
	Word { $[a-z] $[a-zA-Z_\-?/!]* }
	space { $[ \t\r]+ }
	comment { "&" ![\n]* }
	String { '"' (!["\\] | "\\" _)* '"' }
	int { $[1-9]$[0-9]* | "0" }
	float { ("0" | int ) "." $[0-9]+}
	Number { "-"? (int | float) }
	separator { $[,\n] }
	terminator { $[;\n] | @eof }
	newline { "\n" }
}