%{
  open Ast
%}

%token EOF

%token KWD_EXTERN
%token KWD_FN
%token KWD_RETURN

%token PUNCT_COLON
%token PUNCT_LBRACE
%token PUNCT_LPAREN
%token PUNCT_RARROW
%token PUNCT_RBRACE
%token PUNCT_RPAREN
%token PUNCT_SEMI

%token <int> LIT_NEG_INT
%token <int> LIT_INT
%token <string> IDENT

%start <program> program

%%

program:
| decls=decl* EOF { decls }

decl:
| func=func { DeclFunc func }
| extern=extern_func { DeclExternFunc extern }

func:
| KWD_FN name=IDENT PUNCT_LPAREN PUNCT_RPAREN body=body { { name; body } }

extern_func:
| KWD_EXTERN KWD_FN name=IDENT PUNCT_LPAREN PUNCT_RPAREN PUNCT_SEMI { { name } }

body:
| PUNCT_LBRACE stmts=stmt* PUNCT_RBRACE { { stmts; ret=ExprUnit } }

stmt:
| KWD_RETURN expr=expr PUNCT_SEMI { StmtReturn expr }

expr:
| i=LIT_NEG_INT { ExprLit (LitNegInt i) }
| i=LIT_INT { ExprLit (LitInt i) }