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¶Fill in the Middle (FIM)

The Fill in the Middle (FIM) feature allows you to generate code between a starting prompt and an optional ending suffix. This is particularly useful for completing partially written code or generating a specific section of code within a predefined structure.

Tip

FIM is ideal when you already know the beginning and end of a code block, but need assistance generating the code in between.

¶Concept

• Prompt: The beginning of the code (e.g., function declaration, docstring).
• Suffix: The ending of the code (e.g., return statement or closing brace).
• Stop: An optional string indicating where the generation should stop.

The model fills the gap between the prompt and the suffix.

¶Example without streaming

use Partitech\PhpMistral\MistralClient;

$client = new MistralClient($apiKey);
$model_name = "codestral-2405";

$prompt  = "Write response in php:\n";
$prompt .= "/** Calculate date + n days. Returns \DateTime object */";
$suffix  = 'return $datePlusNdays;\n}';

try {
    $result = $client->fim(
        params: [
            'prompt'       => $prompt,
            'model'        => $model_name,
            'suffix'       => $suffix,
            'temperature'  => 0.7,
            'top_p'        => 1,
            'max_tokens'   => 200,
            'min_tokens'   => 0,
            'stop'         => 'string',
            'random_seed'  => 0
        ]
    );
} catch (\Throwable $e) {
    echo $e->getMessage();
    exit(1);
}

echo $result->getMessage();

Result:

function datePlusNDays(\DateTime $date, int $n) {
    $datePlusNdays = clone $date;
    $datePlusNdays->modify("+$n days");
    return $datePlusNdays;
}

Note

The fim() method automatically combines the prompt, the generated content, and the suffix to form the complete output.

¶Example with streaming

To stream the response token by token as it is generated, enable the stream option.

try {
    $result = $client->fim(
        params: [
            'prompt'       => $prompt,
            'model'        => $model_name,
            'suffix'       => $suffix,
            'temperature'  => 0.7,
            'top_p'        => 1,
            'max_tokens'   => 200,
            'min_tokens'   => 0,
            'stop'         => 'string',
            'random_seed'  => 0
        ],
        stream: true
    );

    /** @var \Partitech\PhpMistral\Message $chunk */
    foreach ($result as $chunk) {
        echo $chunk->getChunk();
    }
} catch (MistralClientException $e) {
    echo $e->getMessage();
    exit(1);
}

Streaming output:

function datePlusNDays(\DateTime $date, int $n) {
    $datePlusNdays = clone $date;
    $datePlusNdays->modify("+$n days");
    return $datePlusNdays;
}

¶Parameters Overview

Tip

• Adjust temperature and top_p together to balance between creativity and precision.
• Use random_seed to reproduce the same output across runs.

Warning

Ensure that both the prompt and suffix align contextually, so the model can generate meaningful content in between.