0003

Status: Accepted

Context

The set targets Lua 5.1. pslua reads each fork's foreign file (src/*.lua) and extracts the exported values. Its reader does not parse Lua: it requires every exported value to be wrapped in parentheses and finds the end of a value by matching those parentheses (Foreign.hs, valueParser).

Decision

• Generated and hand-written Lua must run on Lua 5.1: no table.unpack, bit32, utf8, or the // operator; math.pow and math.atan2 do exist; array-style tables are 1-indexed; Lua 5.1 mangles some Lua 5.3 string escapes, so keep FFI escapes 5.1-safe.
• Every FFI export is parenthesised: return { name = (<value>), ... }. A bare function ... end or an unparenthesised expression fails to parse.

Consequences

• luacheck --std lua51 is the gate that catches 5.1 violations, for example table.pack/unpack/move slipping in from Lua 5.2/5.3 habits.
• Lua formatters that strip "redundant" parentheses (StyLua) break the FFI reader; the set uses lua-format, which preserves them (see 0007).
• Relaxing the parenthesis requirement would mean teaching pslua to find a value's end without the parentheses, which needs real Lua parsing. That is a compiler decision, recorded in the pslua repository, not here.