layout toplevel ;
layout "let" ;
layout stop "in" ;

entrypoints [Def], Exp ;

token Id ((letter|digit|["[]_"])+) ;

comment "--" ;
comment "{-" "-}" ;

TypeDef. Def ::= "type" TypeSig1 [Decl] ;
VarDef.  Def ::= Id ":" TypeSig ":=" Exp ;
separator Def ";" ;

Decl. Decl  ::= Id ":" TypeSig ;
[].  [Decl] ::= ;
(:). [Decl] ::= "|" Decl [Decl];
-- todo custom [Decl]

TypeFun. TypeSig  ::= TypeSig1 "→"  TypeSig ;
TypeApp. TypeSig1 ::= Id [TypeSig2] ;
TypeVar. TypeSig2 ::= Id ;
coercions TypeSig 2;

separator nonempty TypeSig2 "" ;

ExpLet.   Exp  ::= "let" "{" [Assign] "}" "in" Exp2 ;
ExpTyped. Exp1 ::= Exp2 ":" TypeSig ;
ExpAbs.   Exp2 ::= "λ" [Id] "." Exp3 ;
ExpApp.   Exp3 ::= Exp4 [Exp4] ;
ExpVar.   Exp4 ::= Id ;

Assign. Assign ::= Ident "=" Exp1 ;
separator nonempty Assign ";" ;

separator nonempty Exp4 "" ;
coercions Exp 4 ;

separator nonempty Id "" ;