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CLAUDE.md

What This Is

HVM4 is a term rewrite system / runtime for the Interaction Calculus.

  • The theoretical spec is in README.md.
  • The C implementation is in clang/.
  • The C spec is in clang/README.md.

Build and Test

# Build
cd clang && clang -O2 -o main main.c

# Run a file
./clang/main test/file.hvm4 -s -C10

Where:
- `-s` shows performance stats
- `-C10` collapses and flattens superpositions
  - Note: use collapse mode it by default
  - Note: limit it to 10 lines to avoid infinite streams 

# Run all tests
./test/_all_.sh

Code Architecture

File Organization (CRITICAL)

The file path IS the function name. Replace / with _, drop .c:

term/tag.c       →  term_tag()
term/new/lam.c   →  term_new_lam()
prim/add.c       →  prim_add()
wnf/app_lam.c    →  wnf_app_lam()

_.c represents the directory itself:

snf/_.c          →  snf()
collapse/_.c     →  collapse()
parse/term/_.c   →  parse_term()

This is strictly enforced. Read clang/STYLE.md before writing any code.

Key Modules in clang/

  • hvm4.c — root file that #includes everything
  • main.c — CLI entry point
  • term/ — term representation (tag, val, ext, constructors)
  • parse/ — parser (source → AST)
  • wnf/ — weak normal form evaluator (interaction rules)
  • snf/ — strong normal form evaluator
  • prim/ — primitive operations (add, mul, eq, etc.)
  • collapse/ — superposition extraction

Term Representation

64-bit term pointer: SUB(1) | TAG(7) | EXT(24) | VAL(32)

  • SUB: is this heap entry a substitution?
  • TAG: term type (APP, LAM, SUP, etc.)
  • EXT: label/name (24-bit, base64-encoded)
  • VAL: heap address or immediate value

Evaluation

Stack-based WNF evaluator in wnf/_.c. Interaction rules are in wnf/ named by pattern:

  • app_lam.c handles (λx.f a)
  • dup_sup.c handles ! X &L = &R{a,b}
  • etc.

Test Format

Tests are .hvm4 files with expected output in trailing // comments:

@main = ((@add 1) 2)
//3

@main = (&L{1,2} + 3)
//4
//5

Always run all tests after each change.