template

Overview ¶

Package template provides prompt template rendering with variable substitution.

The template engine supports both Go template syntax and a simplified Handlebars-like syntax that is automatically converted before execution.

Syntax ¶

Simple variables use double braces:

Hello, {{name}}!

Conditionals use #if and /if:

{{#if urgent}}URGENT: {{/if}}{{title}}

Iteration uses #each and /each:

{{#each items}}{{.}} {{/each}}

Helper functions can be called with arguments:

{{truncate description 100}}
{{upper name}}

Built-in Functions ¶

• truncate(s string, maxLen int) string - Cut string to max length with ellipsis
• json(v any) string - Convert value to pretty-printed JSON
• upper(s string) string - Convert to uppercase
• lower(s string) string - Convert to lowercase
• trim(s string) string - Remove leading/trailing whitespace
• split(s, sep string) []string - Split string by separator
• join(slice []string, sep string) string - Join strings with separator
• replace(s, old, new string) string - Replace all occurrences
• contains(s, substr string) bool - Check if string contains substring
• hasPrefix(s, prefix string) bool - Check if string starts with prefix
• hasSuffix(s, suffix string) bool - Check if string ends with suffix
• default(val, defaultVal any) any - Return default if val is nil/empty
• indent(s string, spaces int) string - Add spaces to each line
• wrap(s string, width int) string - Wrap text at width

Example ¶

engine := template.NewEngine()
result, err := engine.Render("Hello, {{name}}!", map[string]any{"name": "World"})
// result: "Hello, World!"

Variable Extraction ¶

The Parse method extracts variable names from a template:

vars, err := engine.Parse("{{greeting}}, {{name}}!")
// vars: ["greeting", "name"]

Custom Functions ¶

Add custom functions using AddFunc:

engine.AddFunc("double", func(s string) string { return s + s })
result, _ := engine.Render("{{double .name}}", map[string]any{"name": "ha"})
// result: "haha"

Note: Custom functions use Go template syntax (.name) not Handlebars syntax.

Location ¶

This package is part of the llmkit library:

import "github.com/randalmurphal/llmkit/template"

Package template provides prompt template rendering with variable substitution.