Phase 4: Runtime + Stdlib Implementation Plan¶

For agentic workers: REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development or superpowers:executing-plans.

Goal: Provide builtins (echo), fixed arrays, extern FFI to C, and panic runtime so real programs link.

Architecture: Compiler intrinsics lower to li_rt or libc; extern proc declares C symbols.

Depends on: Phase 3
Blocks: Phase 5

Task 1: echo builtin¶

Files: - Modify: crates/li_types/src/check.rs (treat echo as builtin) - Modify: crates/li_mir/src/lower.rs - Modify: runtime/li_rt.c

• echo accepts string or int (format in rt)
• li_rt_print_string, li_rt_print_int

Task 2: String literals¶

Files: - Modify: lexer, parser, codegen

• NUL-terminated *const i8 or { ptr, len } — pick { ptr, len } struct StringLit as immutable static
• v1: no heap strings; concatenation out of scope

Task 3: Fixed-size arrays codegen¶

Files: - Modify: li_codegen/src/mir_llvm.rs

• array[N,T] as LLVM array type on stack
• Literal index: compile-time OOB error (phase 2) + no runtime check
• Dynamic index: icmp uge + li_bounds_fail

Task 4: extern proc FFI¶

Files: - Modify: parser, typechecker, codegen

extern proc SDL_Init(flags: uint) -> int

• Parse extern proc at module level
• Codegen as LLVM declare with C calling convention

Task 5: Enums and objects¶

Files: - Modify: MIR lower + codegen

• Enum: i32 discriminant
• Object: LLVM struct with named fields, field index from type table

Task 6: Example programs¶

Files: - Create: examples/hello.li (final form with echo) - Create: examples/arrays.li

• lic build examples/hello.li -o hello && ./hello prints hello li

Phase 4 exit gate¶

• hello + arrays examples build and run
• extern proc to puts from libc works in tiny test