ContextOS/etc/yac.txt

num num [0-9]+
key key [a-zA-Z]+

op2 op2 [>=<]
op2 op2 [+\-*/%]
val val mul{ num key }
exp exp val
exp exp val op2 val

stm var var key = exp
stm let let key = exp
stm for for exp
stm if if exp
stm end end
stm cmd pwd

script script rep{ stm }