# sentgen - random sentence generator
#   input:  grammar file; sequence of nonterminals
#   output: a random sentence for each nonterminal

BEGIN {  # read rules from grammar file
    while (getline < "grammar" > 0)
        if ($2 == "->") {
            i = ++lhs[$1]              # count lhs
            rhscnt[$1, i] = NF-2       # how many in rhs
            for (j = 3; j <= NF; j++)  # record them
               rhslist[$1, i, j-2] = $j
        } else
            print "illegal production: " $0
}

{   if ($1 in lhs) {  # nonterminal to expand
        gen($1)
        printf("\n")
    } else 
        print "unknown nonterminal: " $0   
}

function gen(sym,    i, j) {
    if (sym in lhs) {       # a nonterminal
        i = int(lhs[sym] * rand()) + 1   # random production
        for (j = 1; j <= rhscnt[sym, i]; j++) # expand rhs's
            gen(rhslist[sym, i, j])
    } else
        printf("%s ", sym)
}