Epic: v0.2.0 — Mapping Language Core

[alvinreal]

Goal

Implement the morph mapping language: lexer, parser, evaluator. Support core operations (rename, select, drop, set, default, cast) and basic string functions.

Success Criteria

• .morph files parse and execute correctly
• -m and -e CLI flags work
• --dry-run validates mappings without executing
• Path syntax works (dot notation, array indexing)
• Core string functions: join, split, lower, upper, trim, replace

Sub-Issues

Track individual issues labeled v0.2.0

TDD Approach

1. Lexer tests: every token type, edge cases, error reporting with positions
2. Parser tests: every AST node type, malformed input, error messages
3. Evaluator tests: every operation in isolation, then combinations
4. Integration tests: full pipeline with mappings applied