5 Syntax

This chapter contains a schematic specification of the language syntax of LUX. All valid LUX code can be expressed in terms of the following specification. The specification consists of a number of rules. The word on the left-hand side of the first colon of each rule indicates the name of the rule, and the text following the colon specify the valid forms of the rule, separated by vertical bars (|). Lower-case words indicate names of other rules. Upper-case words indicate key LUX syntax words (such as for and else) or names of types of expressions that can appear at those points (such as filename or number), or the expression (empty) which means no input, or c_id, which stands for a common identifier (one starting with an alphabetic character), or s_id, which stands for a special identifier (one starting with one character out of ! $ #). Other characters are expected in the input at the indicated positions. By starting at the very first rule (the one named lines) and successively replacing rule names by one of their valid forms you can end up with any valid piece of LUX code. However, not all possible output of this set of rules yields valid LUX code: whether some code is valid depends also on the classes and contents of the variables and expressions, which is not taken into account in these rules.

lines:

next_line | lines next_line

next_line:

statement | newline

statement:

assignment | routine_execution | routine_definition | selection | loop | return opt_arg | begingroup statement_list endgroup | break | continue | @FILENAME | @@FILENAME | retall | run , var | run var

opt_arg:

(empty) | , expr

begingroup:

begin | {

endgroup:

end | }

assignment:

lhs = expr | lhs op_assign expr

tag_list:

structtag | tag_list structtag

member_spec:

( subsc_list ) | tag_list | member_spec ( subsc_list ) | member_spec tag_list

lhs:

var member_spec | var

var:

c_id | s_id

struct_list:

struct_element | struct_list , struct_element

struct_element:

c_id : expr | expr

expr:

number | string | lhs | var ( ) | expr member_spec | & var | ( range ) | { struct_list } | { } | | ( expr ) | [ expr_list ] | expr + expr | expr - expr | expr * expr | expr / expr | expr % expr | expr ^ expr | expr > expr | expr < expr | expr eq expr | expr ne expr | expr ge expr | expr gt expr | expr lt expr | expr le expr | expr and expr | expr or expr | expr xor expr | expr & expr | expr | expr | expr andif expr | expr orif expr | - expr | + expr

expr_list:

expr | expr_list , expr

range:

expr : expr | expr : * - expr | expr : * | * - expr : expr | * - expr : * - expr | * - expr : * | * - expr | *

subsc:

range | range : + | range : > expr | + | > expr | expr : > expr | expr : +

subsc_or_key:

subsc | expr | key

subsc_list:

subsc_or_key | subsc_list , subsc_or_key

op_assign:

+= | -= | *= | /=

routine_execution:

c_id s_arglist

s_arglist:

(empty) | , arglist

arglist:

arg | arglist , arg

key_param:

c_id

key:

key_param = expr | / key_param

arg:

expr | key

routine_definition:

subr c_id s_paramlist statement_list endsubr | func c_id f_paramlist statement_list endfunc | block c_id statement_list endblock

endsubr:

endsubr | end

endfunc:

endfunc | end

endblock:

endblock | end

paramlist2:

paramlist | paramlist , ellipsis

s_paramlist:

(empty) | , paramlist2

sf_paramlist:

s_paramlist | f_paramlist

paramlist:

c_id | paramlist , c_id

statement_list:

statement | statement_list statement

f_paramlist:

( ) | ( paramlist2 ) | s_paramlist

selection:

if expr opt_then statement opt_else | case case_list opt_else endcase | ncase expr statement_list opt_else endcase

opt_then:

(empty) | then

opt_else:

(empty) | else statement

opt_case_else:

(empty) | else statement | else : statement

case_list:

expr : statement | case_list expr : statement

loop:

for c_id = expr , expr opt_step opt_do statement | repeat statement until expr | do statement while expr | while expr opt_do statement

opt_step:

(empty) | , expr

opt_do: (empty) | do