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const lexemeTypes = []
const newLexemeType = (type, regex, adder) => {
lexemeTypes.push({
type,
regex: new RegExp(`^(${regex})(.*)$`),
adder: adder || (lexemes => { lexemes.push({ type }) })
})
}
const newValueLexeme = (type, regex, converter = v => v) => {
newLexemeType(type, regex, (lexemes, value) => {
lexemes.push({ type, value: converter(value) })
})
}
const newSkippableLexeme = (type, regex) => {
newLexemeType(type, regex, () => {})
}
newValueLexeme('constant', '\\d+', Number)
newLexemeType('d', 'd')
newLexemeType('+', '\\+')
newSkippableLexeme('whitespace', '\\s+')
const lex = (expressionString) => {
let lexemes = []
while (expressionString.length > 0) {
let matched = false
lexemeTypes.forEach(lexemeType => {
let matches = lexemeType.regex.exec(expressionString)
if (matches) {
matched = true
lexemeType.adder(lexemes, matches[1])
expressionString = matches[2]
}
})
if (!matched) {
return 'error'
}
}
return lexemes
}
exports.lex = lex
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