dblock / excalc-rs / 35987320194

98%

push

github

Implement variable assignment (:=)

Adds statement-level variable assignment: `name := expr` evaluates
expr and binds it to name, visible to later statements in the same
input. A full input can now be a `;`- or newline-separated sequence
of statements (assignments and/or plain expressions); the value of
the last statement is the result (an assignment's value is the value
assigned).

Assignment is deliberately a statement, not an expression — it can't
be nested inside a larger expression or chained (`x := y := 5`),
keeping `:=` unambiguous and orthogonal to `=`'s equality meaning.
`pi`/`e` remain reserved and can't be reassigned (a new
CalcError::ReservedIdentifier). Variables don't persist across
separate CLI invocations or MCP tool calls — each `evaluate()` call
still starts from a fresh Context.

- lexer.rs: new Assign (':=') and Semi (';' or newline) tokens;
  newlines are no longer plain whitespace.
- ast.rs: new Stmt enum (Assign/Expr) and Program = Vec<Stmt>.
- parser.rs: parse_program() parses a full program; parse_statement()
  disambiguates 'name :=' via 2-token lookahead.
- eval.rs: eval_program() runs statements against a mutable Context.
- lib.rs: evaluate() now parses/evaluates a program instead of a
  single expression.

Documents the feature in README.md (new Variables section + testable
examples), DESIGN.md (grammar's new statement layer, updated =/?
deviation note), docs/functions/logic.md, and CHANGELOG.md. Full test
suite (207 tests), fmt, and clippy all clean; new code has no
uncovered lines per cargo llvm-cov.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

178 of 178 new or added lines in 4 files covered. (100.0%)

3236 of 3245 relevant lines covered (99.72%)

63000.45 hits per line