(rontolisp) docs

Compiled read/load Limitations

The JVM read/load reuse the JDK at runtime (Long.parseLong, BigInteger, Double.parseDouble, java.nio.file), so they parse the same value kinds as the interpreter: integers, big integers, floats, strings, symbols, nil/t, lists, 'quote and #'function.

In every backend read parses one S-expression from a line of stdin: blank and comment-only lines are skipped (it keeps reading until a line contains a datum), EOF returns nil, and a form must fit on a single line.

The WASM reader has a hand-written parser and is narrower:

  • Integers are 31-bit. Integer tokens are parsed to i31 and wrap on overflow; there is no big-integer parsing.
  • Floats are read. A decimal token (optional leading -, digits, one ., e.g. 1.0, -2.5, .5, 5.) parses to an f64-backed float, matching how float literals compile. There is no exponent (1e3) or grouping-comma support in the reader, and a token with two dots or any non-digit (e.g. 1.2.3, foo.bar) stays a symbol.
  • Symbol interning is runtime-backed. Symbols that appear in the compiled program resolve to the same offset the compiled eval uses; symbols seen only at runtime (e.g. a lambda parameter inside a loaded file) are interned in a runtime table so repeated occurrences stay consistent.
  • load requires a preopened directory. It opens the file via WASI path_open relative to the first preopened directory (fd 3), so run with --dir.

The reader-level syntax that the frontend resolves at read time — backquote templates, #| ... |# block comments, #+/#- feature conditionals, and the *features* substitution (see Data Types) — is not understood by the runtime reader of compiled output: a file read at runtime via read/read-from-string/a computed load must not use them.

require/provide are compile-time directives on the compiled backends, so they are not understood by the runtime load of compiled output: a file read at runtime via a computed or nested load must not contain them (only a literal, top-level require/provide works, consumed at compile time) — the same limitation as a runtime-loaded file's package directives (see Packages).

read-from-string reuses the same runtime reader, so on the compiled backends it parses the same value kinds as read (and #\ character literals parsed at runtime are out of scope on both compilers — character literals written directly in source are compiled fully). parse-integer is independent of the reader and works on all three backends; its :start/:end keywords are interpreter-only, and on the compiled backends the keyword names must be literal. Both are also usable as first-class values (#'parse-integer, #'read-from-string) on all three backends — passed via the single-argument wrapper, so the keyword/optional arguments are not available through the function value.