filtress/parser/parser.go

package parser

import (
  "io"
  "fmt"
  "strings"
  "strconv"
)

type Parser struct {
  s   *scanner
  row int
  buffer  struct {
    token Token
    size  int
  }
}

type Expression struct {
  Opperator   rune
  Opperand    int
  Variable    string
}

type Procedure struct {
  Kind          string
  Expressions   []Expression
}

type Loop struct {
  Counter     int
  Procedures  []Procedure
}

type AST struct {
  Procedures  []Procedure
  Loops   []Loop
}




func (p *Parser) scan() (current Token) {
	if p.buffer.size != 0 {
		p.buffer.size = 0
		return p.buffer.token
	}

	current = p.s.scan()
	p.buffer.token = current
	return
}


func (p *Parser) unscan() {
  p.buffer.size = 1
}


func (p *Parser) parseExpressions(equals bool) []Expression {
  var exprs []Expression = make([]Expression, 0, 4)
  for {
    t := p.scan()
    ex := Expression{}

    if t.kind == Opperator {
      ex.Opperator = rune(t.val[0])
      t = p.scan()
    } else if t.kind == Number || t.kind == Text {
      ex.Opperator = '='
    } else if t.kind == Newline {
      p.unscan()
      break
    } else {
        panic(fmt.Sprintf("Parse error: Invalid token %q on \033[1mline %d\033[0m", t.val, p.row))
    }

    if t.kind == Number {
      ex.Opperand, _ = strconv.Atoi(t.val)
    } else if t.kind == Text {
      if isVariable(t.val) {
        ex.Variable = strings.ToUpper(t.val)
      } else {
        panic(fmt.Sprintf("Parse error: Invalid variable %q on \033[1mline %d\033[0m", t.val, p.row))
      }
    }

    exprs = append(exprs, ex)

    t = p.scan()
    if t.kind == Separator {
      continue
    }

    if t.kind == Newline || t.kind == End {
      p.unscan()
      break
    }

  }
  return exprs
}

func (p *Parser) parseProcedure() Procedure {
  out := Procedure{}
  t := p.scan()
  t.val = strings.ToUpper(t.val)

  if isValidProcedure(t.val) {
    out.Kind = t.val
  } else {
    panic(fmt.Sprintf("Parse error: Invalid procedure call %q on \033[1mline %d\033[0m", t.val, p.row))
  }

  t = p.scan()
  switch t.kind {
  case Number, Text:
    p.unscan()
    out.Expressions = p.parseExpressions(true)
  case Opperator:
    p.unscan()
    out.Expressions = p.parseExpressions(false)
  case End, Newline:
    p.unscan()
  default:
    panic(fmt.Sprintf("Parse error: Invalid token %q on \033[1mline %d\033[0m", t.val, p.row))
  }

  return out
}


func (p *Parser) parseLoop() []Procedure {
  t := p.scan()
  var lcount int

  if t.kind == Number {
    lcount, _ = strconv.Atoi(t.val)
  } else {
    panic(fmt.Sprintf("Parse error: Loop declared, but not followed by a number on \033[1mline %d\033[0m", p.row))
  }

  procedures := make([]Procedure,0, lcount * 2)

  L:
  for {
    t = p.scan()
    switch t.kind {
    case Newline:
      p.row++
    case Illegal:
      panic(fmt.Sprintf("Parse error: Illegal token %q on \033[1mline %d\033[0m", t.val, p.row))
    case Opperator:
      panic(fmt.Sprintf("Parse error: Opperator %q outside of a procedure call on \033[1mline %d\033[0m", t.val, p.row))
    case Separator:
      panic(fmt.Sprintf("Parse error: Illegal field separator ':' on \033[1mline %d\033[0m", p.row))
    case End:
      panic(fmt.Sprintf("Parse error: Encountered EOF before END of loop on \033[1mline %d\033[0m", p.row))
    case Number:
      panic(fmt.Sprintf("Parse error: Number %q outside of procedure call on \033[1mline %d\033[0m", t.val, p.row))
    case Text:
      if strings.ToUpper(t.val) == "END" {
        break L
      }
      if strings.ToUpper(t.val) == "BEG" {
        subloop := p.parseLoop()
        procedures = append(procedures, subloop...)

      } else {
        p.unscan()
        procedure := p.parseProcedure()
        procedures = append(procedures, procedure)
      }
    }
  }

  fullLoop := make([]Procedure, 0, len(procedures) * lcount)

  for i := lcount;i > 0; i-- {
    fullLoop = append(fullLoop, procedures...)
  }

  return fullLoop
}


func (p *Parser) Parse() AST {
  p.row = 1
  tree := AST{}

  L:
  for {
    t := p.scan()
    switch t.kind {
    case Newline:
      p.row++
    case Illegal:
      panic(fmt.Sprintf("Parse error: Illegal token %q on \033[1mline %d\033[0m", t.val, p.row))
    case Opperator:
      panic(fmt.Sprintf("Parse error: Opperator %q outside of a procedure call on \033[1mline %d\033[0m", t.val, p.row))
    case Separator:
      panic(fmt.Sprintf("Parse error: Illegal field separator ':' on \033[1mline %d\033[0m", p.row))
    case End:
      break L
    case Number:
      panic(fmt.Sprintf("Parse error: Number %q outside of procedure call on \033[1mline %d\033[0m", t.val, p.row))
    case Text:
      if strings.ToUpper(t.val) == "BEG" {
        loopVal := p.parseLoop()
        tree.Procedures = append(tree.Procedures, loopVal...)
      } else {
        p.unscan()
        procedure := p.parseProcedure()
        tree.Procedures = append(tree.Procedures, procedure)
      }
    }
  }

  return tree
}

func isValidProcedure(p string) bool {
  switch p {
    case "RG1", "RG2", "LOC", "BEG", "END", "RED", "GET",
    "GRN", "BLU", "APH", "COL", "APY", "MOD", "LOX", "LOY":
      return true
  }
  return false
}

func isVariable(v string) bool {
  v = strings.ToUpper(v)
  switch v {
  case "WID", "HIG", "RG1", "RG2", "LOX", "LOY",
  "RED", "BLU", "GRN", "APH":
    return true
  }
  return false
}

func NewParser(r io.Reader) *Parser {
	return &Parser{s: NewScanner(r)}
}