Template Expression

Template expressions let you generate text dynamically from runtime data.

Syntax Overview

Use double curly braces to evaluate an expression:

{{ expression }}

Expression rules:

• Plain text outside {{ ... }} is returned as-is.
• Function calls are space-separated: {{ functionName arg1 arg2 }}.
• Use double quotes for arguments with spaces: {{ lowercase "HELLO WORLD" }}.
• Nested calls use parentheses: {{ uppercase (lowercase "MiXeD") }}.
• Curly braces inside quoted strings are allowed (e.g. regex quantifiers like "[0-9]{3}").
• Block helpers use # / / tags with an optional {{else}} section.
• If an expression fails, output is rendered as: {{ERROR: ...}}.

Data Source

Most templates read values from JSON runtime data through jsonPointer.

Example runtime JSON:

{
 "project": {
  "name": "Nara",
  "version": 12,
  "active": true,
  "tags": ["vision", "flow"]
 },
 "node": {
  "id": "node-07"
 }
}

Data Function: jsonPointer

jsonPointer fetches a value from JSON (e.g. node output) using a JSON Pointer path.

{{ jsonPointer pointer }}
{{ jsonPointer pointer indent }}

Arguments:

• pointer (required): JSON Pointer path, for example "/project/name".
• indent (optional): integer indentation for pretty JSON output when target is object/array.

Behavior:

• String result: returns string value.
• Number result: converted to string.
• Boolean result: returns true or false.
• Null result: returns empty string.
• Object/array result:
  • no indent or indent = 0: compact JSON string.
  • indent > 0: pretty-printed JSON.

jsonPointer Examples

1. Read a string value:

   Template: {{ jsonPointer "/project/name" }}
   Output:   Nara

2. Read a numeric value:

   Template: {{ jsonPointer "/project/version" }}
   Output:   12

3. Read a boolean value:

   Template: {{ jsonPointer "/project/active" }}
   Output:   true

4. Read an array (compact JSON):

   Template: {{ jsonPointer "/project/tags" }}
   Output:   ["vision","flow"]

5. Read an array (pretty JSON):

   Template: {{ jsonPointer "/project/tags" 2 }}
   Output:
   [
   "vision",
   "flow"
   ]

6. Chain with other functions:

   Template: {{ uppercase (jsonPointer "/project/name") }}
   Output:   NARA

7. Invalid path handling:

   Template: {{ jsonPointer "/project/unknown" }}
   Output:   {{ERROR: JSON pointer error: ...}}

jsonPointer and Data References (Flow runtime)

In flow execution, string values that match the internal data-reference prefix are resolved automatically:

• Frame reference in idFrames -> converted to Base64 string.
• Vector frame reference in idVFrames -> first frame converted to Base64.
• This resolution is recursive for objects and arrays returned by jsonPointer.

Practical effect:

• If JSON contains a data-reference token, jsonPointer can return encoded image content instead of the raw token.

Block Helpers: #if / #unless

Conditional blocks inspired by Handlebars #if / #unless.

{{#if condition}}
  then content
{{else}}
  else content
{{/if}}

{{#unless condition}}
  content when falsy
{{else}}
  content when truthy
{{/unless}}

Rules:

• condition is any expression (often a nested call such as (jsonPointer "/project/active")).
• {{else}} is optional.
• Blocks can be nested.
• Unclosed or mismatched blocks render as {{ERROR: ...}}.

Truthiness

A condition value is falsy when it is one of:

• empty string ""
• "false"
• "0"
• "null"
• "[]"

Everything else is truthy (including "{}").

• #if renders the then-branch when the condition is truthy.
• #unless renders the then-branch when the condition is falsy.

Examples

{{#if (jsonPointer "/project/active")}}
enabled
{{else}}
disabled
{{/if}}

Output:

enabled

{{#unless (jsonPointer "/project/tags")}}
no tags
{{else}}
has tags
{{/unless}}

Output:

has tags

Conditional Functions

Excel-style helpers for inline conditionals. Use the same truthiness rules as #if / #unless.

if

{{ if condition valueIfTrue valueIfFalse }}

Arguments:

• condition (required)
• valueIfTrue (required)
• valueIfFalse (required)

{{ if (jsonPointer "/project/active") "ON" "OFF" }}

Output:

ON

AND

Returns "true" if all arguments are truthy, otherwise "false".

{{ AND arg1 arg2 ... }}

OR

Returns "true" if any argument is truthy, otherwise "false".

{{ OR arg1 arg2 ... }}

Combined example

{{ if (AND (jsonPointer "/project/active") (jsonPointer "/project/name")) "ready" "wait" }}

Output:

ready

String Functions

lowercase

Converts the first argument to lowercase.

{{ lowercase "Hello WORLD" }}

Output:

hello world

uppercase

Converts the first argument to uppercase.

{{ uppercase "Hello WORLD" }}

Output:

HELLO WORLD

capitalize

Uppercases only the first character of the first argument.

{{ capitalize "nara flow" }}

Output:

Nara flow

Padding Function

stringPad

Pads a string to target length.

{{ stringPad value targetLength padToken direction }}

Arguments:

• value (required): source string.
• targetLength (required): non-negative integer.
• padToken (optional): token used for padding, default is single space.
• direction (optional): start or end, default is start.

Examples:

{{ stringPad "7" 3 "0" "start" }}

Output:

007

{{ stringPad "ID" 6 "-" "end" }}

Output:

ID----

{{ stringPad "ABC" 8 "xy" "end" }}

Output:

ABCxyxyx

Errors:

• Missing required args -> error.
• Non-numeric length -> error.
• Negative length -> error.
• Invalid direction (not start or end) -> error.

Regex Functions

Excel-like helpers modeled on REGEXTEST / REGEXEXTRACT / REGEXREPLACE.

case_sensitivity (optional for all three):

• 0 (default): case-sensitive
• 1: case-insensitive

regexTest

Checks whether any part of text matches pattern. Returns "true" or "false".

{{ regexTest text pattern }}
{{ regexTest text pattern case_sensitivity }}

{{ regexTest "ABC-123" "[0-9]" }}

Output:

true

regexExtract

Extracts text matching pattern.

{{ regexExtract text pattern }}
{{ regexExtract text pattern return_mode }}
{{ regexExtract text pattern return_mode case_sensitivity }}

return_mode:

• 0 (default): first match string, or empty string if none
• 1: all matches as a compact JSON array, e.g. ["a","b"]
• 2: capturing groups from the first match as a JSON array (groups 1..n)

{{ regexExtract "Order 123-45" "[0-9]+-[0-9]+" }}

Output:

123-45

{{ regexExtract "a1 b2 c3" "[0-9]" 1 }}

Output:

["1","2","3"]

{{ regexExtract "ab-cd" "([a-z]+)-([a-z]+)" 2 }}

Output:

["ab","cd"]

regexReplace

Replaces matches of pattern in text with replacement.

{{ regexReplace text pattern replacement }}
{{ regexReplace text pattern replacement occurrence }}
{{ regexReplace text pattern replacement occurrence case_sensitivity }}

occurrence:

• 0 (default): replace all matches
• n > 0: replace only the nth match from the start
• n < 0: replace only the |n|th match from the end

Replacement supports ECMAScript backreferences such as $1, $2.

{{ regexReplace "555-123-4567" "[0-9]{3}-" "***-" }}

Output:

***-***-4567

{{ regexReplace "555-123-4567" "[0-9]{3}-" "***-" 1 }}

Output:

***-123-4567

Date and Context Functions

datetimeNow

Returns current local datetime.

{{ datetimeNow }}
{{ datetimeNow format }}

Format aliases (case-insensitive):

Notes:

• Unknown format text falls back to ISO.

Example:

{{ datetimeNow "DATE" }}

Output:

2026-05-23

toolId

Returns current flow tool ID from runtime context.

{{ toolId }}

Example output:

tool-image-segmentation

nodeId

Returns current flow node ID from runtime context.

{{ nodeId }}

Example output:

node-07

Nested Expression Examples

{{ uppercase (jsonPointer "/project/name") }}

{{ stringPad (jsonPointer "/project/version") 4 "0" "start" }}

{{ capitalize (lowercase "NARA TEMPLATE") }}

{{ if (OR "false" (jsonPointer "/project/active")) "yes" "no" }}

{{#if (AND (jsonPointer "/project/active") (jsonPointer "/project/name"))}}
ready
{{else}}
wait
{{/if}}

{{ regexReplace (jsonPointer "/node/id") "[0-9]+" "XX" }}

Troubleshooting

• Unknown function: ...
  • Function name is not registered in current runtime.
• jsonPointer function requires at least one argument
  • Missing pointer path.
• JSON pointer error: ...
  • Invalid path or path does not exist.
• stringPad function requires a numeric length argument
  • Target length is not an integer.
• if function requires three arguments
  • Missing valueIfTrue or valueIfFalse.
• Unclosed #if block / Mismatched block close
  • Missing or mismatched {{/if}} / {{/unless}}.
• regexTest pattern error: ... / regexExtract pattern error: ... / regexReplace pattern error: ...
  • Invalid regular expression pattern.