token whitespace = /[ \n\t]+/ [ skip ];
token upper_identifier = /[A-Z_][a-z_A-Z0-9]*/;
token lower_identifier = /[a-z_][a-z_A-Z0-9]*/;
token kw_data = /data/;
token kw_type = /type/;
token kw_defn = /defn/;
token tkn_ocurly = /{/;
token tkn_ccurly = /}/;
token tkn_oparen = /\(/;
token tkn_cparen = /\)/;
token tkn_eq = /=/;
token tkn_comma = /,/;

rule S = program;

rule program
    = definition program?
    ;

rule definition
    = kw_data upper_identifier tkn_eq data_body
    | kw_type upper_identifier tkn_eq type_body
    | kw_defn lower_identifier params? tkn_eq defn_body
    ;

rule data_body
    = tkn_ocurly data_elems tkn_ccurly
    ;

rule data_elems
    = data_elem
    | data_elem tkn_comma data_elems
    ;

rule data_elem
    = upper_identifier
    | upper_identifier tkn_oparen data_elem_types tkn_cparen
    ;

rule data_elem_types
    = type
    | type tkn_comma data_elem_types
    ;

rule type_body
    = tkn_ocurly type tkn_ccurly
    ;

rule params
    = lower_identifier params?
    ;

rule defn_body
    = tkn_ocurly expr tkn_ccurly
    ;

rule expr
    = lower_identifier
    ;

rule type
    = upper_identifier
    ;