Class: Fusion::Parser

Inherits:
Object
  • Object
show all
Includes:
AST
Defined in:
lib/fusion/parser.rb

Constant Summary collapse

PRIMARY_STARTERS =

Tokens that can begin a unary operand — used to decide whether ! has an operand or is the bare !null.

%i[number string true_kw false_kw null_kw bang minus slash tilde
lbracket lbrace lparen ident at atat].freeze
GUARDEDPAT_STARTERS =

Tokens that can begin a guardedpat (used to detect whether ! is followed by a payload pattern or stands alone).

%i[number string true_kw false_kw null_kw minus
lbracket lbrace ident].freeze

Constants included from AST

AST::ArrayItem, AST::ArraySpread, AST::Clause, AST::Identifier, AST::KeyValuePair, AST::ObjectSpread, AST::PatternItem, AST::PatternPair, AST::PatternRest

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(tokens) ⇒ Parser

Returns a new instance of Parser.



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# File 'lib/fusion/parser.rb', line 18

def initialize(tokens)
  @toks = tokens
  @i = 0
end

Class Method Details

.parse_file(src, site:) ⇒ Object

Parse a complete program. The lexer and parser report failures by raising ParseError; this single entry point rescues them and returns a standardized syntax_error value, so no caller ever sees a raw Ruby error. site is the syntax_error's {origin:, file:} context.



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# File 'lib/fusion/parser.rb', line 27

def self.parse_file(src, site:)
  toks = Lexer.new(src).tokens
  p = new(toks)
  expr = p.parse_expr
  p.expect(:eof)
  expr
rescue ParseError => err
  Interpreter::ErrorVal.from_runtime(kind: "syntax_error", **site, operation: "parsing code", input: src, message: err.message)
end

.parse_repl(src, site:) ⇒ Object

Parse one REPL entry — a statement (identifier "=" expr) or a bare expression — returning an AST::Statement::Assignment / AST::Expression, or, like parse_file, a standardized syntax_error value instead of ever raising. The REPL uses the error/non-error distinction to tell "keep editing" (didn't parse yet) from "evaluate now" (a complete statement or expression).



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# File 'lib/fusion/parser.rb', line 42

def self.parse_repl(src, site:)
  toks = Lexer.new(src).tokens
  p = new(toks)
  entry = p.parse_repl_entry
  p.expect(:eof)
  entry
rescue ParseError => err
  Interpreter::ErrorVal.from_runtime(kind: "syntax_error", **site, operation: "parsing code", input: src, message: err.message)
end

Instance Method Details

#advance ⇒ Object 



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# File 'lib/fusion/parser.rb', line 535

def advance = (@toks[@i].tap { @i += 1 })

#at?(type) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/fusion/parser.rb', line 534

def at?(type) = peek.type == type

#expect(type) ⇒ Object

Raises:



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# File 'lib/fusion/parser.rb', line 536

def expect(type)
  t = peek
  raise ParseError, "Expected #{type} but got #{t.type} (#{t.value.inspect}) at #{t.pos}" unless t.type == type
  advance
end

#fold_operator(operands, member) ⇒ Object

A single-operand run collapses to that operand; otherwise fold n-ary.



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# File 'lib/fusion/parser.rb', line 248

def fold_operator(operands, member)
  operands.length == 1 ? operands.first : pipe_operator(operands, member)
end

#looks_like_function? ⇒ Boolean

Look ahead from current position (just after "(") to decide if this is a function literal: is there a top-level "=>" before the matching ")"?

Returns:

  • (Boolean) 


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# File 'lib/fusion/parser.rb', line 379

def looks_like_function?
  depth = 0
  j = @i
  while j < @toks.length
    t = @toks[j]
    case t.type
    when :lparen, :lbracket, :lbrace then depth += 1
    when :rparen, :rbracket, :rbrace
      return false if depth.zero? # hit our closing ) first
      depth -= 1
    when :arrow
      return true if depth.zero?
    when :eof
      return false
    end
    j += 1
  end
  false
end

#name_ref(path) ⇒ Object

--- Desugaring helpers ---------------------------------------------------



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# File 'lib/fusion/parser.rb', line 233

def name_ref(path) = Expression::FileRef.new(variety: :name, path: path)

#negate(expr) ⇒ Object

-x: a numeric literal folds to a negative literal; anything else negates.



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# File 'lib/fusion/parser.rb', line 253

def negate(expr)
  if expr.is_a?(Expression::Lit) && expr.value.is_a?(Numeric)
    Expression::Lit.new(value: -expr.value)
  else
    pipe_into(expr, "negate")
  end
end

#op_member(member) ⇒ Object

@OP.member, a shadowable reference.



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# File 'lib/fusion/parser.rb', line 236

def op_member(member) = Expression::Member.new(obj: name_ref("OP"), key: member)

#parse_additive ⇒ Object

A run of +/- folds into one @OP.sum; each - term is negated.



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# File 'lib/fusion/parser.rb', line 117

def parse_additive
  terms = [parse_multiplicative]
  folded = false
  while at?(:plus) || at?(:minus)
    negated = at?(:minus)
    advance
    term = parse_multiplicative
    terms << (negated ? negate(term) : term)
    folded = true
  end
  folded ? pipe_operator(terms, "sum") : terms.first
end

#parse_and ⇒ Object 



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# File 'lib/fusion/parser.rb', line 88

def parse_and
  operands = [parse_equality]
  while at?(:andand)
    advance
    operands << parse_equality
  end
  fold_operator(operands, "and")
end

#parse_array ⇒ Object 



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# File 'lib/fusion/parser.rb', line 301

def parse_array
  expect(:lbracket)
  items = []
  until at?(:rbracket)
    if at?(:spread)
      advance
      items << ArraySpread.new(value: parse_expr)
    else
      items << ArrayItem.new(value: parse_expr)
    end
    break unless at?(:comma)
    advance
  end
  expect(:rbracket)
  Expression::ArrLit.new(items: items)
end

#parse_arraypat ⇒ Object

p_array (reference.md §2.5). Items are p_guardeds — never error patterns. The grammar's two arms (with / without a rest) become two phases: the loop parses leading items up to an optional single ...rest; once a rest is consumed, the inner loop parses trailing items only, so a second ... lands in parse_guardedpat as an unexpected token. There is no seen_rest flag — "at most one rest" is enforced by the shape of the loop.



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# File 'lib/fusion/parser.rb', line 466

def parse_arraypat
  expect(:lbracket)
  items = []
  until at?(:rbracket)
    if at?(:spread)
      items << parse_pattern_rest
      while at?(:comma)
        advance
        break if at?(:rbracket) # trailing comma
        raise ParseError, "a pattern may contain at most one `...rest` (at #{peek.pos})" if at?(:spread)
        items << PatternItem.new(pattern: parse_guardedpat)
      end
      break
    end
    items << PatternItem.new(pattern: parse_guardedpat)
    break unless at?(:comma)
    advance
  end
  expect(:rbracket)
  Pattern::PArr.new(items: items)
end

#parse_corepat ⇒ Object 



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# File 'lib/fusion/parser.rb', line 440

def parse_corepat
  t = peek
  case t.type
  when :number, :string then advance; Pattern::PLit.new(value: t.value)
  when :true_kw, :false_kw, :null_kw then advance; Pattern::PLit.new(value: t.value)
  when :minus then advance; Pattern::PLit.new(value: -expect(:number).value)  # negative literal
  when :lbracket then parse_arraypat
  when :lbrace then parse_objectpat
  when :ident
    advance
    t.value == "_" ? Pattern::PWild.new(dummy: nil) : Pattern::PBind.new(name: t.value)
  when :bang
    # `!pat` is only valid as a clause's top-level pattern, never inside an
    # array element, object member, or error payload.
    raise ParseError, "`!pat` may only appear as a clause's top-level pattern (at #{t.pos})"
  else
    raise ParseError, "Unexpected token in pattern: #{t.type} at #{t.pos}"
  end
end

#parse_equality ⇒ Object 



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# File 'lib/fusion/parser.rb', line 97

def parse_equality
  operands = [parse_ordering]
  while at?(:eqeq)
    advance
    operands << parse_ordering
  end
  fold_operator(operands, "equal")
end

#parse_errpat ⇒ Object 



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# File 'lib/fusion/parser.rb', line 418

def parse_errpat
  expect(:bang)
  if GUARDEDPAT_STARTERS.include?(peek.type)
    Pattern::PErr.new(inner: parse_guardedpat)               # "!" guardedpat
  else
    Pattern::PErr.new(inner: Pattern::PWild.new(dummy: nil)) # bare "!" — matches any error, binds nothing
  end
end

#parse_expr ⇒ Object 



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# File 'lib/fusion/parser.rb', line 69

def parse_expr
  parse_or
end

#parse_fileref ⇒ Object 



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# File 'lib/fusion/parser.rb', line 290

def parse_fileref
  expect(:at)
  return Expression::FileRef.new(variety: :self, path: nil) unless at?(:path)

  # A reference is eligible for builtin/stdlib fallback (:name) iff it has no
  # "../"; downward paths stay eligible, only "../" forces file-only (:path).
  # The lexer produced the whole path as one tight token (see Lexer#try_lex_path).
  path = advance.value
  Expression::FileRef.new(variety: path.include?("..") ? :path : :name, path: path)
end

#parse_function_or_group ⇒ Object

A "(" begins a grouped expression, a function literal, or — when empty — the clause-less function (). A function is a comma-separated list of pattern => expr; we detect one by scanning for a top-level => before the matching ). () matches nothing (so it yields null for any normal input and propagates errors).



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# File 'lib/fusion/parser.rb', line 348

def parse_function_or_group
  expect(:lparen)
  if at?(:rparen)
    advance
    return Expression::FuncLit.new(clauses: [])
  end
  if looks_like_function?
    clauses = []
    loop do
      pat = parse_pattern
      expect(:arrow)
      body = parse_expr
      clauses << Clause.new(pattern: pat, body: body)
      if at?(:comma)
        advance
        break if at?(:rparen) # trailing comma
      else
        break
      end
    end
    expect(:rparen)
    Expression::FuncLit.new(clauses: clauses)
  else
    e = parse_expr
    expect(:rparen)
    e
  end
end

#parse_guardedpat ⇒ Object 



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# File 'lib/fusion/parser.rb', line 427

def parse_guardedpat
  inner = parse_corepat
  if at?(:question)
    advance
    # A predicate is a full pipe so it may chain functions: `a ? b | c` tests
    # `a | b | c`. It stops at `=>`, `,`, `]`, `}`, `)` like any expression.
    pred = parse_pipe
    Pattern::PGuard.new(inner: inner, pred_expr: pred)
  else
    inner
  end
end

#parse_multiplicative ⇒ Object

A run of *// folds into one @OP.product (each / term inverted); %/// are binary and break the run. Standard left-to-right: a * b % c is (a * b) % c.



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# File 'lib/fusion/parser.rb', line 132

def parse_multiplicative
  node = parse_pipe
  run = nil                                  # accumulating product-run terms, or nil
  loop do
    if at?(:star) || at?(:slash)
      inverted = at?(:slash)
      advance
      term = parse_pipe
      term = pipe_into(term, "invert") if inverted
      if run
        run << term
      else
        run = [node, term]
      end
    elsif at?(:percent) || at?(:slashslash)
      node = pipe_operator(run, "product") if run
      run = nil
      op = at?(:percent) ? "modulo" : "quotient"
      advance
      node = pipe_operator([node, parse_pipe], op)
    else
      break
    end
  end
  run ? pipe_operator(run, "product") : node
end

#parse_object ⇒ Object

Fixed keys must be distinct (the ObjLit data rule); a repeat is a clean syntax_error. Keys arriving via ...spread are dynamic and not checked.



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# File 'lib/fusion/parser.rb', line 320

def parse_object
  expect(:lbrace)
  pairs = []
  keys = []
  until at?(:rbrace)
    if at?(:spread)
      advance
      pairs << ObjectSpread.new(value: parse_expr)
    else
      key_tok = expect(:string)
      key = key_tok.value
      raise ParseError, "duplicate key #{key.inspect} (at #{key_tok.pos})" if keys.include?(key)
      keys << key
      expect(:colon)
      pairs << KeyValuePair.new(key: key, value: parse_expr)
    end
    break unless at?(:comma)
    advance
  end
  expect(:rbrace)
  Expression::ObjLit.new(pairs: pairs)
end

#parse_objectpat ⇒ Object

p_object (reference.md §2.5). Leading pairs up to an optional single ...rest, which must come last — only a trailing comma may follow it. Keys must be distinct (the PObj data rule); a repeat is a clean syntax_error.



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# File 'lib/fusion/parser.rb', line 491

def parse_objectpat
  expect(:lbrace)
  pairs = []
  keys = []
  until at?(:rbrace)
    if at?(:spread)
      pairs << parse_pattern_rest
      advance if at?(:comma) && peek(1)&.type == :rbrace # trailing comma
      unless at?(:rbrace)
        raise ParseError, "in an object pattern, `...rest` must come last (at #{peek.pos})"
      end
      break
    end
    key_pos = peek.pos
    pair = parse_pattern_pair
    raise ParseError, "duplicate key #{pair.key.inspect} (at #{key_pos})" if keys.include?(pair.key)
    keys << pair.key
    pairs << pair
    break unless at?(:comma)
    advance
  end
  expect(:rbrace)
  Pattern::PObj.new(pairs: pairs)
end

#parse_or ⇒ Object

--- Operator sugar (reference §2.7) -------------------------------------- The ladder below desugars every operator to a pipe into an @OP.* member (or, for the map-pipes, a stdlib call). Tightest to loosest:

postfix · unary (! - / ~) · pipe (| |: |? |+) · * / % // · + - · ?? · == · && · ||

@OP.* is a shadowable :name reference, so a local @OP reskins the operators.



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# File 'lib/fusion/parser.rb', line 79

def parse_or
  operands = [parse_and]
  while at?(:oror)
    advance
    operands << parse_and
  end
  fold_operator(operands, "or")
end

#parse_ordering ⇒ Object

?? (compare) is binary and left-associative — it does not fold.



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# File 'lib/fusion/parser.rb', line 107

def parse_ordering
  node = parse_additive
  while at?(:qq)
    advance
    node = pipe_operator([node, parse_additive], "compare")
  end
  node
end

#parse_pattern ⇒ Object

---- Patterns ---- ---- Pattern grammar (mirrors reference.md §2.5 EBNF) ------------------ pattern = p_error | p_guarded p_error = "!" | "!" p_guarded p_guarded = p_core [ "?" predicate ] p_core = p_literal | p_bind | p_wildcard | p_array | p_object Note: p_core does NOT include p_error. The "no nested !pat" property falls out of the grammar shape — p_error is only reachable from pattern (a clause's top level), never from inside arrays, objects, or another error's payload. No flag-threading is needed.



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# File 'lib/fusion/parser.rb', line 409

def parse_pattern
  at?(:bang) ? parse_errpat : parse_guardedpat
end

#parse_pattern_pair ⇒ Object

p_pair = string ":" p_guarded



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# File 'lib/fusion/parser.rb', line 526

def parse_pattern_pair
  key = expect(:string).value
  expect(:colon)
  PatternPair.new(key: key, pattern: parse_guardedpat)
end

#parse_pattern_rest ⇒ Object

p_rest = "..." [ identifier ] — the single rest binder, shared by array and object patterns. Callers parse it only at a rest position and then continue with items/pairs only, which is what holds a pattern to one rest.



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# File 'lib/fusion/parser.rb', line 519

def parse_pattern_rest
  expect(:spread)
  name = at?(:ident) ? advance.value : nil
  PatternRest.new(name: name)
end

#parse_pipe ⇒ Object 



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# File 'lib/fusion/parser.rb', line 159

def parse_pipe
  node = parse_unary
  loop do
    if at?(:pipe)
      advance
      node = Expression::Pipe.new(left: node, right: parse_unary)
    elsif at?(:pipemap) || at?(:pipefilter) || at?(:pipereduce)
      target = { pipemap: "map", pipefilter: "filter", pipereduce: "reduce" }[peek.type]
      advance
      arg = Expression::ObjLit.new(pairs: [
        KeyValuePair.new(key: "c", value: node),
        KeyValuePair.new(key: "f", value: parse_unary),
      ])
      node = Expression::Pipe.new(left: arg, right: name_ref(target))
    else
      break
    end
  end
  node
end

#parse_postfix ⇒ Object 



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# File 'lib/fusion/parser.rb', line 205

def parse_postfix
  node = parse_primary
  loop do
    if at?(:dot)
      advance
      key = expect(:ident).value
      node = Expression::Member.new(obj: node, key: key)
    elsif at?(:lbracket)
      advance
      idx = parse_expr
      if at?(:equals)
        advance
        value = parse_expr
        expect(:rbracket)
        node = Expression::IndexSet.new(obj: node, idx: idx, value: value)
      else
        expect(:rbracket)
        node = Expression::Index.new(obj: node, idx: idx)
      end
    else
      break
    end
  end
  node
end

#parse_primary ⇒ Object 



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# File 'lib/fusion/parser.rb', line 261

def parse_primary
  t = peek
  case t.type
  when :number, :string then advance; Expression::Lit.new(value: t.value)
  when :true_kw, :false_kw, :null_kw then advance; Expression::Lit.new(value: t.value)
  when :lbracket then parse_array
  when :lbrace then parse_object
  when :lparen then parse_function_or_group
  when :ident then advance; Expression::Ident.new(name: t.value)
  when :at then parse_fileref
  when :atat then parse_superref
  else raise ParseError, "Unexpected token #{t.type} (#{t.value.inspect}) at #{t.pos}"
  end
end

#parse_repl_entry ⇒ Object

A leading identifier = marks a statement; anything else is an expression. (A bare identifier is itself a valid expression, so the = is the decider.)



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# File 'lib/fusion/parser.rb', line 54

def parse_repl_entry
  if at?(:ident) && peek(1)&.type == :equals
    parse_statement
  else
    parse_expr
  end
end

#parse_statement ⇒ Object

statement = identifier "=" expr (REPL only; files contain one expr)



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# File 'lib/fusion/parser.rb', line 63

def parse_statement
  name = expect(:ident).value
  expect(:equals)
  AST::Statement::Assignment.new(name: name, expression: parse_expr)
end

#parse_superref ⇒ Object

@@ is super. Bare @@ is super of the current file's own name; @@name (or a downward @@dir/name) is a stable reference to that name — it skips the sibling name.fsn, resolving builtin → stdlib, so a user's local shadow can't intercept it. @@../… is meaningless (super of an upward path) and falls through to a parse error.

Raises:



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# File 'lib/fusion/parser.rb', line 281

def parse_superref
  expect(:atat)
  return Expression::FileRef.new(variety: :super, path: nil) unless at?(:path)

  tok = advance
  raise ParseError, "`@@` cannot take an upward path (at #{tok.pos})" if tok.value.include?("..")
  Expression::FileRef.new(variety: :super_name, path: tok.value)
end

#parse_unary ⇒ Object

Unary prefixes: !x builds an error (bare ! is !null); -x negates, /x inverts, ~x is logical not. All bind tighter than |.



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# File 'lib/fusion/parser.rb', line 187

def parse_unary
  if at?(:bang)
    advance
    PRIMARY_STARTERS.include?(peek.type) ? Expression::ErrLit.new(payload: parse_unary) : Expression::ErrLit.new(payload: nil)
  elsif at?(:minus)
    advance
    negate(parse_unary)
  elsif at?(:slash)
    advance
    pipe_into(parse_unary, "invert")
  elsif at?(:tilde)
    advance
    pipe_into(parse_unary, "not")
  else
    parse_postfix
  end
end

#peek(o = 0) ⇒ Object

---- token helpers ----



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# File 'lib/fusion/parser.rb', line 533

def peek(o = 0) = @toks[@i + o]

#pipe_into(expr, member) ⇒ Object

expr | @OP.member



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# File 'lib/fusion/parser.rb', line 239

def pipe_into(expr, member) = Expression::Pipe.new(left: expr, right: op_member(member))

#pipe_operator(operands, member) ⇒ Object

[operands...] | @OP.member



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# File 'lib/fusion/parser.rb', line 242

def pipe_operator(operands, member)
  arr = Expression::ArrLit.new(items: operands.map { |e| ArrayItem.new(value: e) })
  Expression::Pipe.new(left: arr, right: op_member(member))
end