Maple is a lightweight, embeddable template engine written in pure C. It provides variables, conditional logic, loops, arithmetic, comparisons, functions, file includes, and caching, with no dependencies.

Inspired by Go’s text/template — but built for C developers who want speed, simplicity, and full control.

For a quick look at functionality, run: make example && ./example. More detailed examples can found in the examples directory.

To build a shared object for your system, run:

make

When linking, make sure to include the math library with -lm.

• Variable substitution:
  {{ name }}

  A single symbol between the double curly braces indicates a variable. If that variable has been set on the context, this will be rendered with whitespace trimmed.

• Function calls:
  Call built‑in or custom C functions

  • {{ lower name }}
  • {{ upper name }}
  • {{ title name }}
  • {{ reverse name }}

• Whitespace trimming:
  Surrounding whitespace inside tags is automatically removed.

• Arithmetic expressions:

  Handles +, -, *, /, () with correct operator precedence. All numbers are handled as doubles. If the value is a whole number the decimal point and trailing 0's will not be displayed. Supports 2 points of precision

• Comparison operators:

  <, >, <=, >=, ==, !=

• Boolean logic:

  Supports &&, ||, !.

• Unified numeric/logical evaluation:

  Same syntax usable anywhere, even inside if or template output.

Additional template files can be loaded from within other templates with the following syntax:

{{ include "another_template.tmpl" }}

{{ if (x + y) >= 10 && age <>; 30 }}
Condition is true
{{ else }}
Condition is false
{{ end }}

All values are HTML escaped by default.

If a value contains HTML or characters that could be replaced by the escaping process, use the safe keyword.

{{ safe var_containing_known_good_html }}

Functions that can error will return a int value of either 0 or 1, 0 for success or 1 for an error. That value is also stored on the ctx value that's passed to the function. The ctx value also carries an error string associated with the error.

int ret = mp_render_segment(ctx, out, tpl, NULL, ".");
if (ret != 0) {
    printf("error code: %d, error code str: %s, error message: %s\n",
        mp_err_code_str(ctx), mp_err_code(ctx), mp_strerror(ctx));
    return 1;
}

This pattern should be used when extending functionality.

All tests can be found in the tests/ directory and are easily extended.

To run:

make tests

Tests are compiled with debug symbols.

Please feel free to open a PR!

Brian Downs @bdowns328

BSD 2 Clause License.