list: stmt [{ ';' stmt }];

prog:     stmts;

stmt: sum;

stmts:    stmt [{ ';' stmt }];

sum: 'let' Name '=' sum | product [{ add | subtract }];

stmt:     assign | print | loop | select;

assign:   Name '=' sum;

print:    'print' sums;

sums:     sum [{ ',' sum }];

loop:     While cmp Do stmts 'od';

While:    'while';

Do:       'do';

select:   'if' cmp Then stmts [ Else stmts ] 'fi';

Then:     'then';

Else:     'else';

cmp:      sum rel;

rel:      eq | ne | gt | ge | lt | le;

eq:       '=' sum;

ne:       '<>' sum;

gt:       '>' sum;

ge:       '>=' sum;

lt:       '<' sum;

le:       '<=' sum;

sum:      product [{ add | subtract }];

add: '+' product;

add:      '+' product;

subtract: '-' product;

subtract: '-' product;

product: signed [{ multiply | divide }];

product:  signed [{ multiply | divide }];

multiply: '*' signed;

multiply: '*' signed;

divide: '/' signed;

divide:   '/' signed;

signed: [ '-' ] term;

signed:   [ '-' ] term;

term: input | number | name | '(' sum ')';

term:     input | number | name | '(' sum ')';

input: 'input' [ Number ];

input:    'input' [ Number ];

number: Number;

number:   Number;

name: Name;

name:     Name;