hakorune/docs/reference/language/EBNF.md

Nyash Grammar (Stage‑2 EBNF)

Status: Fixed for Phase 15 Stage‑2. Parser implementations (Rust/Python/Nyash selfhost) should conform to this subset.

program := stmt* EOF

stmt := 'return' expr | 'local' IDENT '=' expr | 'if' expr block ('else' block)? | 'loop' '('? expr ')' ? block | expr ; expression statement

block := '{' stmt* '}'

expr := logic logic := compare (('&&' | '||') compare)* compare := sum (( '==' | '!=' | '<' | '>' | '<=' | '>=' ) sum)? sum := term (('+' | '-') term)* term := unary (('' | '/') unary) unary := '-' unary | factor

factor := INT | STRING | IDENT call_tail* | '(' expr ')' | 'new' IDENT '(' args? ')' | '[' args? ']' ; Array literal (Stage‑1 sugar, gated) | '{' map_entries? '}' ; Map literal (Stage‑2 sugar, gated)

map_entries := (STRING | IDENT) ':' expr (',' (STRING | IDENT) ':' expr)* [',']

call_tail := '.' IDENT '(' args? ')' ; method | '(' args? ')' ; function call

args := expr (',' expr)*

Notes

• ASI: Newline is the primary statement separator. Do not insert a semicolon between a closed block and a following 'else'.
• Short-circuit: '&&' and '||' must not evaluate the RHS when not needed.
• Unary minus has higher precedence than '*' and '/'.
• IDENT names consist of [A-Za-z_][A-Za-z0-9_]*
• Array literal is enabled when syntax sugar is on (NYASH_SYNTAX_SUGAR_LEVEL=basic|full) or when NYASH_ENABLE_ARRAY_LITERAL=1 is set.
• Map literal is enabled when syntax sugar is on (NYASH_SYNTAX_SUGAR_LEVEL=basic|full) or when NYASH_ENABLE_MAP_LITERAL=1 is set.
• Identifier keys ({name: v}) are Stage‑3 and require either NYASH_SYNTAX_SUGAR_LEVEL=full or NYASH_ENABLE_MAP_IDENT_KEY=1.

Stage‑3 (Gated) Additions

Enabled when NYASH_PARSER_STAGE3=1 for the Rust parser (and via --stage3/NYASH_NY_COMPILER_STAGE3=1 for the selfhost parser):

• try/catch/cleanup

  • try_stmt := 'try' block ('catch' '(' (IDENT IDENT | IDENT | ε) ')' block) ('cleanup' block)?
    • MVP policy: single catch per try。
    • (Type var) or (var) or () are accepted for the catch parameter。

• Block‑postfix catch/cleanup（Phase 15.5）

  • block_catch := '{' stmt* '}' ('catch' '(' (IDENT IDENT | IDENT | ε) ')' block)? ('cleanup' block)?
  • Applies to standalone block statements. Do not attach to if/else/loop structural blocks (wrap with a standalone block when needed).
  • Gate: NYASH_BLOCK_CATCH=1 (or NYASH_PARSER_STAGE3=1).

• throw

  • throw_stmt := 'throw' expr

• Method‑level postfix catch/cleanup（Phase 15.6, gated）

  • method_decl := 'method' IDENT '(' params? ')' block ('catch' '(' (IDENT IDENT | IDENT | ε) ')' block)? ('cleanup' block)?
  • Gate: NYASH_METHOD_CATCH=1（または NYASH_PARSER_STAGE3=1 と同梱）

These constructs remain experimental; behaviour may degrade to no‑op in some backends until runtime support lands, as tracked in CURRENT_TASK.md.