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const { lex } = require('./lexer.js')
let symbols = {}
let newSymbol = (type, nud, lbp, led) => {
symbols[type] = { type, nud, lbp, led }
}
let lexemeToToken = lexeme => {
let token = Object.create(symbols[lexeme.type])
token.value = lexeme.value
return token
}
newSymbol('constant', function() {
return { type: 'constant', value: this.value }
})
newSymbol('d', null, 30, (left, parser) => {
return {
type: 'd',
left: left,
right: parser.expression(29)
}
})
newSymbol('+', null, 20, (left, parser) => {
return {
type: 'add',
left: left,
right: parser.expression(20)
}
})
newSymbol('-', null, 20, (left, parser) => {
return {
type: 'subtract',
left: left,
right: parser.expression(20)
}
})
newSymbol('end', null, -1)
const newParser = (tokens) => {
return {
tokens,
currentToken: 0,
token: function() { return this.tokens[this.currentToken] },
advanceToken: function() { this.currentToken++ },
expression: function(rbp) {
let symbol = this.token()
let left = symbol.nud()
this.advanceToken()
while (rbp < this.token().lbp) {
symbol = this.token()
this.advanceToken()
left = symbol.led(left, this)
}
return left
}
}
}
const parse = expressionString => {
const tokens = lex(expressionString).map(lexemeToToken)
tokens.push(symbols.end)
const parser = newParser(tokens)
return parser.expression(0)
}
exports.parse = parse
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