Synopsis
echo Goal | gawk -f story.awk [ -v Grammar=FILE ] [ -v Seed=NUMBER ]
echo Goal | gawk -f storyp.awk [ -v Grammar=FILE ] [ -v Seed=NUMBER ]
Download
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LAWKER.
Description
This code inputs a set of productions
and outputs a string of words that satisfy the production rules.
This page describes two versions of that system:
story.awk
and
storyp.awk.
The former selects productions at random with equal probability. The latter
allows the user to bias the selection by adding weights at the end of line, after
each production.
Options
- -v Grammar=FILE
- Sets the FILE containing the productions. Defaults to "grammar".
- -v Seed=NUM
-
Sets the seed for the random number generator. Defaults to "1".
A useful idiom for generating random text is to use Seed=$RANDOM
Examples
A Short Example
This grammar..
Sentence -> Nounphrase Verbphrase
Nounphrase -> the boy
Nounphrase -> the girl
Verbphrase -> Verb Modlist Adverb
Verb -> runs
Verb -> walks
Modlist ->
Modlist -> very Modlist
Adverb -> quickly
Adverb -> slowly
... and this input ...
for i in 1 2 3 4 5 6 7 8 9 10;do
echo Sentence |
gawk -f ../story.awk -v Grammar=english.rules -v Seed=$i |
fmt
done
... generates these sentences:
the boy runs very slowly
the girl runs slowly
the boy runs very slowly
the girl walks very very quickly
the boy runs quickly
the girl walks very very slowly
the boy walks very very very very very very quickly
the boy walks very quickly
the girl runs slowly
the girl runs very quickly
A Longer Example
Here is Gahan Wilson's sci-fi plot generator ...
Using the above, we can generate the following stories:
Earth scientists invent giant bugs who want Our Women, And Take
A Few And Leave
Earth is Attacked By tiny lunar superbeings who Under Stand and
Are Not radioactive and can not be killed by the Navy but They Die
From Catching A Cold
Earth scientists invent enormous bugs who are Friendly and and
They Get Married And Live Happily Forever After
Earth is Struck By A Giant cloud and Magically Saved
Earth scientists invent giant bugs who Under Stand and Are Not
radioactive and can not be killed by the Air Force so They Kill
Us
Earth is Attacked By enormous extra Galactic blobs who Under Stand
and Are Not radioactive and can be killed by the Air Force
Earth scientists discover enormous blobs who Under Stand and Are
Not radioactive and can be killed by a Crowd Of Peasants
Earth falls Into Sun and Some Resuced
Earth is Struck By A Giant comet but Is Saved
Earth is Struck By A Giant comet and Is Destroyed
This is generated from the following code:
for i in 1 2 3 4 5 6 7 8 9 10;do
echo
echo Start |
gawk -f ../story.awk -v Grammar=scifi.rules -v Seed=$i |
fmt
done
running on the following grammar:
Start -> Earth IsStressed
IsStressed -> Catestrophes
IsStressed -> Science
IsStressed -> Attack
IsStressed -> Collision
Catestrophes -> Catestrophe and PossibleMegaDeath
Catestrophe -> burnsUp
Catestrophe -> freezes
Catestrophe -> fallsIntoSun
Collision -> isStruckByAGiant Floater AndThen
Floater -> comet
Floater -> asteroid
Floater -> cloud
AndThen -> butIsSaved
AndThen -> andIsDestroyed
AndThen -> andMagicallySaved
PossibleMegaDeath -> everybodyDies
PossibleMegaDeath -> Some GoOn
SomeSaved -> somePeople
SomeSaved -> everybody
SomeSaved -> almostEverybody
GoOn -> dies
GoOn -> Resuced
GoOn -> Saved
Rescued -> isRescuedBy Sizes Extraterestrial Beings
Saved -> butIsSavedBy SomeOne scientists the Science
SomeOne -> earth
SomeOne -> extraterestrial
Science -> scientists DoSomething Sizes Beings Whichetc
DoSomething -> invent
DoSomething -> discover
Attack -> isAttackedBy Sizes Extraterestrial Beings Whichetc
Sizes -> tiny
Sizes -> giant
Sizes -> enormous
Extraterestrial -> martian
Extraterestrial -> lunar
Extraterestrial -> extraGalactic
Beings -> bugs
Beings -> reptiles
Beings -> blobs
Beings -> superbeings
Whichetc -> who WantSomething
WantSomething -> WantWomen
WantSomething -> areFriendly and DenoumentOrHappyEnding
WantSomething -> UnderStand ButEtc
Understand -> areFriendly butMisunderstood
Understand -> misunderstandUs
Understand -> understandUsAllTooWell
Understand -> hungry
DenoumentOrHappyEnding -> Denoument
DenoumentOrHappyEnding -> HappyEnding
Dine -> Hungry and eat us Denoument?
WhichEtc ->
Hungry -> lookUponUsAsASourceOfNourishment
WantWomen -> wantOurWomen, AndTakeAFewAndLeave
ButEtc -> AndAre radioactive and TryToKill
AndAre -> andAre
AndAre -> andAreNot
Killers -> Killer
Killers -> Killer and Killer
Killer -> aCrowdOfPeasants
Killer -> theArmy
Killer -> theNavy
Killer -> theAirForce
Killer -> theMarines
Killer -> theCoastGuard
Killer -> theAtomBomb
TryToKill -> can be killed by Killers
TryToKill -> can not be killed by Killers SoEtc
SoEtc -> butTheyDieFromCatchingACold
SoEtc -> soTheyKillUs
SoEtc -> soTheyPutUsUnderABenignDictatorShip
SoEtc -> soTheyEatUs
SoEtc -> soScientistsInventAWeapon Which
SeEtc -> but Denoument
Which -> whichTurnsThemIntoDisgustingLumps
Which -> whichKillsThem
Which -> whichFails SoEtc
Denomument? ->
Denomument? -> Denoument
Denoument -> aCuteLittleKidConvincesThemPeopleAreOk Ending
Denoument -> aPriestTalksToThemOfGod Ending
Denoument -> theyFallInLoveWithThisBeautifulGirl EndSadOrHappy
EndSadOrHappy -> Ending
EndSadOrHappy -> HappyEnding
Ending -> andTheyDie
Ending -> andTheyLeave
Ending -> andTheyTurnIntoDisgustingLumps
HappyEnding -> andTheyGetMarriedAndLiveHappilyForeverAfter
Biasing the Story
Here is a grammar suitable for storyp.awk. Note that number at end of line that biases how often a
production is selected. For example, "runs" and "slowly" are nine times more likely than other Verbs
and Adverbs.
Sentence -> Nounphrase Verbphrase 1
Nounphrase -> the boy 0.75
Nounphrase -> the girl 0.25
Verbphrase -> Verb Modlist Adverb 1
Verb -> runs 0.9
Verb -> walks 0.1
Modlist -> 0.5
Modlist -> very Modlist 0.5
Adverb -> quickly 0.1
Adverb -> slowly 0.9
The following code executes the biases story generation:
for((i=1;i<=10;i++)); do echo Sentence ; done |
gawk -f ../storyp.awk -v Grammar=englishp.rules
This produces the following output. Note that, usually, we run slowly.
the boy runs very slowly
the boy runs slowly
the girl runs very slowly
the boy runs slowly
the boy runs slowly
the girl walks very slowly
the boy walks slowly
the girl runs slowly
the boy runs slowly
the boy runs slowly
Code
Story.awk
BEGIN {
srand(Seed ? Seed : 1)
Grammar = Grammar ? Grammar : "grammar"
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
if ($0 !~ /^[ \t]*$/)
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 {
gsub(/[A-Z]/," &",sym)
printf("%s ", sym) }
}
Storyp.awk
Storyp.awk is almost the same as story.awk but it is assumed that each line ends in a number
that will bias how often that production gets selected.
BEGIN {
srand(Seed ? Seed : 1)
Grammar = Grammar ? Grammar : "grammar"
while ((getline < Grammar) > 0)
if ($2 == "->") {
i = ++lhs[$1] # count lhs
rhsprob[$1, i] = $NF # 0 <= probability <= 1
rhscnt[$1, i] = NF-3 # how many in rhs
for (j = 3; j < NF; j++) # record them
rhslist[$1, i, j-2] = $j
} else
print "illegal production: " $0
for (sym in lhs)
for (i = 2; i <= lhs[sym]; i++)
rhsprob[sym, i] += rhsprob[sym, i-1]
}
{ 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
j = rand() # random production
for (i = 1; i <= lhs[sym] && j > rhsprob[sym, i]; i++) ;
for (j = 1; j <= rhscnt[sym, i]; j++) # expand rhs's
gen(rhslist[sym, i, j])
} else
printf("%s ", sym)
}
Author
The code comes from
Alfred Aho, Brian Kernighan, and Peter Weinberger from the
book "The AWK Programming Language",
Addison-Wesley, 1988.
The scifi grammar was written by Tim Menzies, 2009, and is based on
Gahan Wilson's sci-fi plot generator:
"The Science Fiction Horror Movie Pocket Computer"
( in "The Year's Best Science Fiction No. 5", edited by
Harry Harrison and Brian Aldiss, Sphere, London, 1972).
