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IMPRAL

Introduction

IMPRAL is a command parsing and evaluation library for a LISP-ish dialect, intended for reasonably ergonomic and specialized command-line input within larger applications, games and frameworks.

A work-in-progress guide to the language itself, is included in the crate documentation; see [crate::guide]/https://docs.rs/impral/latest/impral/guide/index.html.

NOTICE:
Currently incomplete/still in development. Expect breaking changes.
Do not use in production code.

Features

A very basic overview:

  • Basic language similar to LISP/Scheme.
  • Mostly safe and panic-free parser.
  • Conversion to an AST happens only once.
  • AST is linearized; no tree visitor here!
  • A small-ish set of literal types...
    • _
    • null
    • Booleans (true / false)
    • Characters
    • Integers and floats (both 64-bit)
    • Strings (compact at & below 24 bytes)
      • Quoteless strings (barewords)!
    • Byte-Arrays
    • UUID's, prefixed with U.
  • Data structures:
    • Lists (eg: [ 1, 2, 3 ], commas optional)
    • Dicts (eg: { a=1, b=2, c=3 }, commas optional)
    • Radix number lists (0x[C0 +FF -EE])
  • References!
    • Result reference: $
    • Context reference: $$
    • Local references: $my-ref
    • Global references: @my-ref
  • Operators!
    • Arithmetic (+ - * / **)
    • Equality (== != < > <= >=)
    • Misc. (? ! ~ ^ ++ --)
  • Fields and indices!
    • Named fields: _.name
    • Indexed fields: _.[index]
  • Ranges!
    • Any two expressions, that are not themselves ranges, separated by two dots.
    • Optional 'last-inclusive' flag can be set by adding a = after the dots.
    • i.e.: _ .. _ and _ ..= _
  • Pipes!
    • First expression is the source
    • Expressions separated by |
    • Filters: … |? bar | …
    • Folding: … |! 0 min $ $acc | …
    • Collecting: … |!
    • Chaining! … | … |? … | …
  • Fallible operations!
    • Any expression followed by ? gets unwrapped to the default value.
    • Any expression followed by ?! will throw an error.
  • Conditional operations!
    • A && B: B only runs if A succeeds.
    • A || B: B only runs if A fails.
  • Positional parameters: foo _ _
  • Named parameters: foo bar=_ baz=_
  • Subexpressions, enclosed by (…)
  • Pratt/Infix expressions, via = …
  • ...and other small things!

TODO

  • Validation
  • Interpreter