Here's a simple poem generator using Python and the `random` library、This program will generate a short poem with a random theme, rhyming scheme, and structure.

python
import random

List of possible themes
themes = [nature, love, stars, moon, sunset]

List of possible nouns
nouns = {
nature: [mountain, river, tree, flower, lake],
love: [heart, kiss, hug, date, romance],
stars: [star, galaxy, space, planet, universe],
moon: [moonlight, lunar, eclipse, phase, orbit],
sunset: [sun, sky, orange, pink, dusk]
}

List of possible verbs
verbs = {
nature: [sways, grows, flows, shines, blooms],
love: [beats, kisses, hugs, dates, romances],
stars: [twinkles, shines, glitters, sparkles, glows],
moon: [glows, shines, phases, eclipses, orbits],
sunset: [sets, dips, sinks, glows, fades]
}

List of possible adjectives
adjectives = {
nature: [beautiful, serene, calm, peaceful, tranquil],
love: [tender, loving, romantic, warm, fuzzy],
stars: [sparkling, twinkling, glittering, shining, glowing],
moon: [lunar, silvery, glowing, full, bright],
sunset: [orange, pink, red, golden, vibrant]
}

def generate_poem(theme):
poem = []
noun = random.choice(nouns[theme])
verb = random.choice(verbs[theme])
adjective = random.choice(adjectives[theme])

First line
poem.append(fIn the {adjective} {theme}, the {noun} {verb}.)

Second line
poem.append(fIt {verb}s with a gentle, loving light.)

Third line
poem.append(fThe {noun} is so {adjective} and bright.)

Fourth line
poem.append(fIt fills my heart with delight.)

return \n.join(poem)

def main():
print(Welcome to the poem generator!)
theme = random.choice(themes)
print(fToday's theme is: {theme})
print(generate_poem(theme))

if __name__ == __main__:
main()

Example Output:

Welcome to the poem generator!
Today's theme is: sunset
In the vibrant sunset, the sun sets.
It sets with a gentle, loving light.
The sun is so orange and bright.
It fills my heart with delight.

How it works:

1、The program first defines lists of possible themes, nouns, verbs, and adjectives.
2、The `generate_poem` function takes a theme as input and selects a random noun, verb, and adjective from the corresponding lists.
3、It then constructs a short poem using these words.
4、The `main` function selects a random theme and prints out the generated poem.

Adding more features:

* You can add more themes, nouns, verbs, and adjectives to the lists to increase the variety of poems generated.
* You can modify the structure and rhyming scheme of the poem by changing the way the lines are constructed.
* You can also add user input to select the theme or other parameters of the poem.