MinTPL (GitHub)

Minimal Template Programming Language

Description

A minimalistic language for automatic text processing, implemented as a C (17) library for embedding. It is made specifically to be extended by the embedding application. As a language it bears some similarities to Tcl.

Example

File: input.mtpl

Have a look at this [for>[=>adjectives] adj {[=>adj], }]example.

Invokation using mintpl-cli:

$ mintpl-cli -p adjectives="small;silly" input.mtpl
Have a look at this small, silly, example.

For more examples, see the examples folder.

Features/characteristics

• Everything is a string.
• Depth-first evaluation.
• Variables are available as key-value properties.
• Dynamically scoped variable lookup through linked hashtables.
• Not built for speed or continuous operation – this is a “batch job” language.
• Small – at the time of writing a static release build of the entire library is well below 32 KiB.
• Text encoding agnostic (for all eight bit text formats with null termination, including UTF-8).
• Simple syntax:
  • Substitution: [generator>arguments]
    This invokes generator, which is a named function that is implementation defined, with the string arguments. The output is inserted into the current context.
  • Quote: {quoted text}
    Substitutions within quoted text are not evaluated within the current context, but are inserted verbatim.
  • Escape: \c
    Inserts the character c unprocessed into the current context.
  • No special syntax forms; everything else is done using substitutions and quotes.
• Basic built-in generators:
  • :
    Copy generator. The default generator when template parsing begins. Simply outputs its argument string unadultered.
  • ; Copy-and-strip generator. Copies its argument string, but strips any leading and trailing whitespace from it.
  • =
    Lookup generator. Outputs the value of the property with the key specified by the argument string.
  • !
    Nop generator. Does nothing with its argument string. Can be used for comments, when combined with quoting.
  • has_prop
    Returns #t if the property named by the argument string exists, or #f if it doesn’t.
  • \
    Escape generator. Outputs its string argument with all spaces escaped by backslash.
  • macro
    Syntax: [macro>NAME PARAMLIST BODY]
    Defines a parameterized macro identified by NAME. PARAMLIST is a semicolon separated list of property names that will be substituted with arguments provided when expanding the macro, and BODY is the contents on which the substitutions will operate.
  • **
    Syntax: [**>NAME ARGS]
    Expands the macro NAME, substituting each parameter in its parameter list with subsequent words from ARGS. Whitespace in arguments needs to be escaped.
  • let
    Syntax: [let>VARIABLE VALUE]
    Evaluates VARIABLE as a substitution, then sets the property named by the substitution result to the result of evaluating VALUE.
  • for
    Syntax: [for>LIST VARIABLE SUBSTITUTION]
    Iterates over a semicolon separated list of items (items containing semicolons need to escape them). For each iteration, the property VARIABLE will be set to the current list item, and can be accessed from within SUBSTITUTION if the latter is quoted.
  • if
    Syntax: [if>BOOLEAN T_SUBSTITUTION F_SUBSTITUTION]
    Evaluates T_SUBSTITUTION if BOOLEAN is the string #t, or F_SUBSTITUTION if it is #f. Any other value of BOOLEAN will result in a syntax error.
  • not
    Evaluates its boolean argument, turning #t to #f and vice versa, and throwing syntax error on any other values.
  • eq gt lt ge le
    Binary comparison generators – equals, greater than, less than, greater or equal, and less or equal. Compares the first argument with the second. The arguments can be quoted substitutions, which will be evaluated.
  • #
    Arithmetics generator. Implements a minimal infix arithmetics parser, that works with floating point numbers, and understands parentheses as well as the following set of operators:
    • +: Addition
    • -: Subtraction
    • *: Multiplication
    • /: Division
    • %: Modulo (remainder)
    • ^: Power of
  • range
    Syntax: [range>START END STEP]
    Generates a semicolon separated list of numbers between START and END (non-inclusive). STEP is optional if START is lower than END, and determines the speed and direction between the generated steps. (If omitted, will default to a value of 1.)
  • len
    Syntax [len>LIST]
    Generates the number of elements in LIST.
  • ()
    Syntax [()>LIST INDEX]
    List index lookup generator. Outputs the INDEX'th element in LIST.

Known omissions/Future improvements

• Currently there’s a lack of built in string manipulation generators.
• Debugging is harder than necessary due to a lack of friendly error messages and debug state output.
• Output is very sensitive to input whitespace – indentation requires some care to not affect output.
• No API documentation.

Building/installing

The project is built using CMake (version 3.5 or higher).

1. Create a build directory (preferrably named build) in the repository root.
2. From within the build directory, issue cmake .. -DCMAKE_BUILD_TYPE=Release.
   • To create a debug build, change CMAKE_BUILD_TYPE to Debug.
   • To build a shared library, set the SHARED_LIBRARY variable from the command line: cmake .. -DCMAKE_BUILD_TYPE=Debug -DSHARED_LIBRARY=1
3. A project will now have been generated, based on whatever build system is the platform default. Build and install as you most commonly would (if in doubt, type make).
4. Upon successful completion, the library file will be located directly within the build directory.
   • Tests can be run by invoking the executables in the tests subdirectory.
   • There’s a proof-of-concept standalone tool in the standalone folder, called mintpl-cli. It can be used to process templates that only make use of built-in generators.
5. To install, build the install target, with superuser privileges if necessary. This will install both the library and a pkg-config recipe. On Linux you may need to run ldconfig after installing.

License

MinTPL is released under the MIT License.