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!

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TODO

• Validation
• Interpreter