Sexpr

A ruby compilation framework around s-expressions.

Example

# Let load a grammar defined in YAML
grammar = SexpGrammar.load(<<-YAML)
  rules:
    # alternative rule
    bool_expr:
      - bool_and
      - bool_or
      - bool_not
      - var_ref
      - bool_lit

    # non-terminal
    bool_and:
      - [ bool_expr, bool_expr ]
    bool_or:
      - [ bool_expr, bool_expr ]
    bool_not:
      - [ bool_expr ]
    bool_lit:
      - [ truth_value ]
    var_ref:
      - [ var_name ]

    # terminals
    var_name:
      !ruby/regexp /^[a-z]+$/
    truth_value:
      - true
      - false
YAML

Checking the structure of s-expressions

# the grammar can be used to verify the structure of s-expressions
grammar === [:bool_and, [:bool_not, [:var_ref, "x"]], [:bool_lit, true]]
# => true

grammar === [:bool_and, [:bool_lit, "true"]]
# => false (second term is missing)

Including s-expression tools

# the grammar can also be used to automatically have support on top of
# such s-expressions
expr = grammar.sexpr([:bool_lit, true])

expr.sexpr_type
# => :bool_lit

expr.sexpr_body
# => [true]

Links

https://github.com/blambeau/sexpr