Why AsciiChem?

AsciiMath is excellent at what it does: typography for mathematics. It assumes a math data model — superscripts and subscripts are positional adornments on the previous expression.

Chemistry is not math typography. Chemistry has its own first-class concepts — atoms, bonds, reactions, electron configurations — that AsciiMath collapses into a uniform soup of ^ and _ markers.

The five gaps

1. Prefix isotopes

Chemistry writes ^14C, _6Li, Ca^2+. AsciiMath has no way to bind a prefix marker to the next atom — it forces a phantom {} carrier ({}^14C), so the isotope is bound to an empty element. The atom itself never sees the isotope.

2. Reactions

No native syntax for stoichiometric coefficients, reaction arrows (->, <=>), conditions above or below the arrow, or spectator ions.

3. Electron configurations

No representation for orbital occupancy (1s^2 2s^2 2p^6), term symbols (^3P_2), spin multiplicity, or quantum wells.

4. Bonds and structures

No syntax for single / double / triple / dative / wedge / hash bonds, ring structures, or stereochemistry — all things LaTeX’s chemfig provides.

5. Embedded mathematics

Equilibrium constants, rate laws, Arrhenius expressions — chemistry publications embed math. AsciiMath has no escape hatch from itself.

What AsciiChem does about each

1. Prefix markers bind to the following atom. The grammar enforces this: ^14 followed by C is one parse unit. The model field Atom#isotope carries the binding.
2. First-class Reaction model. Reactants, products, arrow type (:forward, :reverse, :equilibrium, :resonance), and conditions (Conditions(above:, below:)).
3. ElectronConfiguration model. Orbital/occupancy pairs plus optional term symbol.
4. Bond model with kind enum (:single, :double, :triple, :wedge, :hash, :dative, :wavy). Structural diagrams delegate to mn/elk-rb for SVG layout.
5. EmbeddedMath wraps a Plurimath formula. Backtick-delimited runs are parsed by Plurimath::Asciimath; the result sits in the chemistry tree as a typed node.

Design principles

• Plain-keyboard ASCII. Anything a chemist can type without leaving the home row.
• Model-driven. Every parse yields a typed tree. Render to any format without round-tripping through text.
• Round-trippable. parse(s).to_text == s for canonical s.
• Open/closed. New constructs are new model classes; new outputs are new formatters. Existing code stays untouched.
• IUPAC-aligned. Where AsciiChem’s spelling differs from mhchem, the IUPAC Green Book is the tiebreaker.

Continue to Getting started to install and try it.