2.3 KiB
Parser
This includes the parser and generated ast.
Parslet is really great in that it:
- does not generate code but instean gives a clean dsl to define a grammar
- uses ruby modules so one can split the grammars up
- has support for binary operators with presedence and binding
- has a seperate tranform stage to generate an ast layer
Especially the last point is great. Since it is seperate it does not clutter up the actual grammar. And it can generate a layer that has no links to the actual parser anymore, thus saving/automating a complete tranformation process.
Operator list from http://stackoverflow.com/questions/21060234/ruby-operator-precedence-table
N A M Operator(s) Description
1 R Y ! ~ + boolean NOT, bitwise complement, unary plus (unary plus may be redefined from Ruby 1.9 with +@)
2 R Y ** exponentiation 1 R Y - unary minus (redefine with -@)
2 L Y * / % multiplication, division, modulo (remainder) 2 L Y + - addition (or concatenation), subtraction
2 L Y << >> bitwise shift-left (or append), bitwise shift-right 2 L Y & bitwise AND
2 L Y | ^ bitwise OR, bitwise XOR (exclusive OR) 2 L Y < <= >= > ordering
2 N Y == === != =~ !~ <=> equality, pattern matching, comparison (!= and !~ may not be redefined prior to Ruby 1.9)
2 L N && boolean AND 2 L N || boolean OR
2 N N .. ... range creation (inclusive and exclusive) and boolean flip-flops
3 R N ? : ternary if-then-else (conditional) 2 L N rescue exception-handling modifier
2 R N = assignment 2 R N **= *= /= %= += -= assignment 2 R N <<= >>= assignment 2 R N &&= &= ||= |= ^= assignment
1 N N defined? test variable definition and type 1 R N not boolean NOT (low precedence) 2 L N and or boolean AND, boolean OR (low precedence) 2 N N if unless while until conditional and loop modifiers