M2compiler-V3/docs/summary_iochan-files.md

Step: IOChan over files

Tag v3-iochan-files. Suite 130/130; fixpoint OK (bootstrap/fixpoint.sh, image 2,103,316 bytes).

What changed

IOChan now covers files as well as the standard streams, so a program can treat a file and stdin/stdout uniformly through one ChanId:

• OpenRead(name), OpenWrite(name) → ChanId (a failed open yields a closed channel: IsOpen = FALSE).
• Close(VAR cid) — closes and clears the handle.
• IsOpen(cid).
• ReadString(cid, VAR s) — reads one line (the newline is dropped) into the NUL-terminated string; ReadInt(cid) reads a signed decimal integer (skipping leading blanks).

The existing standard channels and operations (StdIn/Out/ErrChan, ReadChar, WriteChar, WriteString, WriteLn, WriteInt) are unchanged. Operations on a closed/failed channel stay safe no-ops (ReadChar returns 0C).

Bridge additions

• runtime/syslib/SysShim.def/.mod: freadint, freadline.
• runtime/syslib/shim.c: m2freadline (line read into a descriptor, newline dropped, header set to the length). m2freadint already existed (used by Files).

Test

compiler/tests/iochanfile_prog.mod (IOChanFileProg, exit 3): writes "line one\n-7\n" through a channel to gen_ssa/_iochan_tmp.txt, closes, reopens for reading, and checks the line (ReadString → "line one") and the integer (ReadInt → -7). The harness removes the temporary file before and after.

Notes

• Close takes cid by reference so it can set it to NIL; this mirrors the ISO-ish "release the channel" shape.
• ReadString truncates to the destination capacity.
• Files keeps its own direct shim binding for now; IOChan could become its base layer in a later step.

Files

stdlib/iochan.def/.mod, runtime/syslib/SysShim.def/.mod, runtime/syslib/shim.c, compiler/tests/iochanfile_prog.mod, compiler/run_tests.sh, docs/features.md.