langchaingo/examples/prompt-template-example

Prompt Template Example

This example demonstrates the core features of LangChain Go's prompt template system.

Features Demonstrated

1. Basic Templates - Simple variable substitution using Go templates
2. Template Formats - Using different template syntaxes (Go, Jinja2, F-string)
3. Partial Variables - Pre-filling some template variables
4. Chat Templates - Creating structured chat prompts
5. Optional Sanitization - HTML escaping for untrusted data

Running the Example

go run main.go

Key Concepts

Template Formats

LangChain Go supports three template formats:

• Go Templates (default): {{ .variable }}
• Jinja2: {{ variable }}
• F-strings: {variable}

Security

By default, templates render without sanitization for maximum compatibility. When working with untrusted user input, enable sanitization:

result, err := prompts.RenderTemplate(
    template,
    prompts.TemplateFormatGoTemplate,
    data,
    prompts.WithSanitization(), // Enables HTML escaping
)

Partial Variables

Partial variables let you pre-fill template values:

template := prompts.PromptTemplate{
    Template: "{{.greeting}}, {{.name}}!",
    InputVariables: []string{"name"},
    PartialVariables: map[string]any{
        "greeting": "Hello",
    },
}