# These two functions are to be used in "grammar scripts"
 proc define {name content} {
    proc $name {} [list expand $content]
    }
 proc defchoice {name choices} {
    proc $name {} [list choice $name $choices]
    }

 # Helper functions
 proc expand str {subst $str}
 proc choice {name choices} {
    set idx [expr int(floor(rand()*[llength $choices]))]
    return [expand [lindex $choices $idx]]
    }

 # Demo "grammar script" -- translated exam.pb from the dada engine distribution -- "generates intimidating but bogus exam questions"
 proc exam {} {
    defchoice question {
        [question-2] 
        [question-2]
        {[question-2] Be sure to refer to [issue] in your answer.}
        {[question-2] Include [evidence-type].}}
    defchoice question-2 {
        {Compute the [something-of ] of [something].}
        {Are [plural] [classification]? Discuss.}
        {Is [singular] [classification]? Discuss.}
        {Express [something] in [express-in-what].}
        {Show that the [something-of ] of [something] is [result].}}
    defchoice issue {{[theorem-source]'s Theorem} {[theory-type] theory}
        "Plutonium Atom Totality" {the [ordinal] law of [law-of-this]}}
    defchoice theorem-source {Godel Wibbel Abian Turing Euler Fermat Bell}
    defchoice theory-type {game set match interstice information ring group graph}
    defchoice law-of-this {thermodynamics "conservation of matter" gravity}
    defchoice express-in-what  {"canonical form" "normal form" {the [tag] domain}}
    defchoice something-of {[something-of-2] {[adjective] [something-of-2]} 
        {[tag]-[something-of-2]}}
    defchoice adjective {canonical minimal maximal inverse}
    defchoice something-of-2 {closure determinant matrix path correlation}
    define plural {[adjective] [plural-2]}
    defchoice plural-2 {trees matrices}
    define singular {[adjective] [singular-2]}
    defchoice singular-2 {search factorisation}
    defchoice result {number "{ }" infinity uncomputable "the null set"}
    defchoice evidence-type {flowcharts "Feynman diagrams" "Venn diagrams"}
    defchoice something {[number] [set-of-numbers]}
    define set-of-numbers {{ [numbers] }}
    defchoice numbers {{[number][numbers]} [number]}
    defchoice number {{[digit][number]} [digit]}
    defchoice digit {0 1 2 3 4 5 6 7 8 9}
    define classification {[tag]-complete}
    defchoice tag {[greek-letter] [roman-letter] {[roman-letter] [roman-letter]}}
    defchoice roman-letter {A B C D E F G H I J K L M N O P Q R S T U V W X Y Z}
    defchoice greek-letter {alpha beta gamma delta epsilon lambda sigma theta phi rho omega}
    defchoice ordinal {first second third fourth fifth}
    return [question]
 }

 # Run demo code
 catch { console show }
 puts [exam]