diff --git a/src/error.ts b/src/error.ts
index 924222ac..ac6b445d 100644
--- a/src/error.ts
+++ b/src/error.ts
@@ -1,17 +1,20 @@
 import { TokenName } from './parser/parser'
 import { indexToLocation, LocationRange, prettyIndex, prettyLocation } from './location'
 import { Source } from './source'
+import { LexerToken } from './lexer/lexer'
 
 export interface SyntaxErrorInfo {
-    tokenChain: TokenName[],
     expected: TokenName[],
     got: TokenName,
     location: LocationRange
 }
 
+export const prettyLexerError = (token: LexerToken): string => {
+    return `lexer error: unknown token \`${token.value}\``
+}
+
 export const prettySyntaxError = (error: SyntaxErrorInfo): string => {
-    const chain = error.tokenChain.filter(n => !n.endsWith('_')).slice(-2).join('/')
-    return `syntax error: expected \`${error.expected}\`, got \`${error.got}\`, while parsing \`${chain}\``
+    return `syntax error: expected \`${error.expected}\`, got \`${error.got}\``
 }
 
 export const prettySourceMessage = (message: string, index: number, source: Source): string => {
diff --git a/src/index.ts b/src/index.ts
index 296fab3d..a16dbc17 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,7 +2,8 @@ import { compactToken, flattenToken, parse } from './parser/parser'
 import { tokenize } from './lexer/lexer'
 import { readFileSync } from 'fs'
 import { join, resolve } from 'path'
-import { prettySourceMessage, prettySyntaxError } from './error'
+import { prettyLexerError, prettySourceMessage, prettySyntaxError } from './error'
+
 
 const version = JSON.parse(readFileSync(join(__dirname, '..', 'package.json')).toString()).version
 
@@ -16,10 +17,14 @@ if (!path) {
     console.log(usage)
     process.exit()
 }
-
 const source = { str: readFileSync(resolve(path)).toString(), filename: path }
 
-const token = parse(tokenize(source.str))
+const tokens = tokenize(source.str)
+if ('name' in tokens) {
+    console.error(prettySourceMessage(prettyLexerError(tokens), tokens.location.start, source))
+    process.exit(1)
+}
+const token = parse(tokens)
 if ('expected' in token) {
     console.error(prettySourceMessage(prettySyntaxError(token), token.location.start, source))
     process.exit(1)
diff --git a/src/lexer/lexer.spec.ts b/src/lexer/lexer.spec.ts
index fd031fe3..c43c5195 100644
--- a/src/lexer/lexer.spec.ts
+++ b/src/lexer/lexer.spec.ts
@@ -1,13 +1,23 @@
-import { tokenize } from './lexer'
+import { LexerToken, tokenize } from './lexer'
 import { expect } from '@jest/globals'
+import { prettyLexerError } from '../error'
 
 describe('lexer', () => {
+
+    const testTokenize = (code: string): LexerToken[] => {
+        const tokens = tokenize(code)
+        if ('name' in tokens) {
+            throw Error(prettyLexerError(tokens))
+        }
+        return tokens
+    }
+
     it('tokenize basic', () => {
         const code = `\
 let main = (): Unit {
 	print(4)
 }`
-        const tokens = tokenize(code)
+        const tokens = testTokenize(code)
         expect(tokens.map(t => [t.name, t.value])).toEqual([
             ['let-keyword_', 'let'],
             ['identifier', 'main'],
@@ -29,28 +39,28 @@ let main = (): Unit {
     })
 
     it('tokenize number literal simple', () => {
-        expect(tokenize('14')).toEqual([
+        expect(testTokenize('14')).toEqual([
             { name: 'number', value: '14', location: { start: 0, end: 1 } },
             { name: 'eof', value: '', location: { start: 2, end: 2 } }
         ])
     })
 
     it('tokenize string literal', () => {
-        expect(tokenize(`"string 123 \n ok"`)).toEqual([
+        expect(testTokenize(`"string 123 \n ok"`)).toEqual([
             { name: 'string', value: `"string 123 \n ok"`, location: { start: 0, end: 16 } },
             { name: 'eof', value: '', location: { start: 17, end: 17 } }
         ])
     })
 
     it('tokenize char literal', () => {
-        expect(tokenize(`'?'`)).toEqual([
+        expect(testTokenize(`'?'`)).toEqual([
             { name: 'char', value: `'?'`, location: { start: 0, end: 2 } },
             { name: 'eof', value: '', location: { start: 3, end: 3 } }
         ])
     })
 
     it('tokenize expression', () => {
-        const tokens = tokenize(`1+call("str").ok() / (12 - a())`)
+        const tokens = testTokenize(`1+call("str").ok() / (12 - a())`)
         expect(tokens.map(t => [t.name, t.value])).toEqual([
             ['number', '1'],
             ['plus', '+'],
diff --git a/src/lexer/lexer.ts b/src/lexer/lexer.ts
index 2a9da2cc..75ed9341 100644
--- a/src/lexer/lexer.ts
+++ b/src/lexer/lexer.ts
@@ -40,7 +40,6 @@ export const lexerTokenNames = <const>[
     'colon_',
     'comma_',
     'equals_',
-    'semicolon_',
 
     // dynamic
     'identifier',
@@ -102,7 +101,7 @@ export const isWhitespace = (char: string): boolean => char === ' ' || char ===
 
 export const isNewline = (char: string): boolean => char === '\n' || char === '\r'
 
-export const tokenize = (code: String): LexerToken[] => {
+export const tokenize = (code: String): LexerToken[] | LexerToken => {
     const pos = { pos: 0 }
     const chars = code.split('')
     const tokens: LexerToken[] = []
@@ -127,11 +126,11 @@ export const tokenize = (code: String): LexerToken[] => {
         if (parseStringLiteral(chars, tokens, pos)) {
             continue
         }
-        throw Error(`unknown token \`${chars[pos.pos]}\``)
+        return createToken(<LexerTokenName>'unknown', chars[pos.pos], pos)
     }
 
     pos.pos++
-    tokens.push(createToken('eof', '', pos))
+    tokens.push(createToken('eof', '', pos, pos.pos - 1))
 
     return tokens
 }
@@ -244,7 +243,7 @@ const parseStringLiteral = (chars: string[], tokens: LexerToken[], pos: { pos: n
 const createToken = (
     name: LexerTokenName,
     value: string, pos: { pos: number },
-    start: number = pos.pos - 1
+    start: number = pos.pos
 ): LexerToken => {
     return { name, value, location: { start, end: pos.pos - 1 } }
 }
diff --git a/src/parser/locate.ts b/src/parser/locate.ts
new file mode 100644
index 00000000..d333011f
--- /dev/null
+++ b/src/parser/locate.ts
@@ -0,0 +1,50 @@
+import { LexerTokenName } from '../lexer/lexer'
+import { ParseBranch, ParserTokenName, rules, TokenName, Transform } from './parser'
+
+export const firstTokens = (token: TokenName): Set<LexerTokenName> => {
+    const rule = rules.get(<ParserTokenName>token)
+    if (rule) {
+        return new Set(rule.branches.flatMap(b => [...transformFirstTokens({
+            name: <ParserTokenName>token,
+            branch: b
+        })]))
+    } else {
+        return new Set([<LexerTokenName>token])
+    }
+}
+
+const transformFirstTokens = (transform: Transform, index: number = 0): Set<LexerTokenName> => {
+    if (index >= transform.branch.length) {
+        return new Set()
+    }
+    const tokens: Set<LexerTokenName> = new Set()
+    const t = <LexerTokenName>transform.branch[index]
+    const rule = rules.get(<ParserTokenName>t)
+    if (rule) {
+        if (canMatchEmpty(rule.name)) {
+            transformFirstTokens(transform, index + 1).forEach(t => tokens.add(t))
+        }
+        firstTokens(rule.name).forEach(t => tokens.add(t))
+    } else {
+        tokens.add(t)
+    }
+    return tokens
+}
+
+const canMatchEmpty = (token: TokenName): boolean => {
+    const rule = rules.get(<ParserTokenName>token)
+    if (rule) {
+        return rule.branches.some(b => branchCanMatchEmpty(b))
+    } else {
+        return token === 'e'
+    }
+}
+
+const branchCanMatchEmpty = (branch: ParseBranch): boolean => {
+    for (let t of branch) {
+        if (!canMatchEmpty(t)) {
+            return false
+        }
+    }
+    return true
+}
diff --git a/src/parser/parser.spec.ts b/src/parser/parser.spec.ts
index be72bd21..a86a3c16 100644
--- a/src/parser/parser.spec.ts
+++ b/src/parser/parser.spec.ts
@@ -1,12 +1,15 @@
 import { tokenize } from '../lexer/lexer'
 import { expect } from '@jest/globals'
 import { compactToken, flattenToken, parse, ParserTokenName, Token } from './parser'
-import { prettySyntaxError } from '../error'
+import { prettyLexerError, prettySyntaxError } from '../error'
 
 describe('parser', () => {
 
     const parseToken = (source: string, root: ParserTokenName = 'program'): Token => {
         const tokens = tokenize(source)
+        if ('name' in tokens) {
+            throw Error(prettyLexerError(tokens))
+        }
         const token = parse(tokens, root)
         if ('expected' in token) {
             throw Error(prettySyntaxError(token))
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index 744d8bd0..4f91b52a 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -3,6 +3,7 @@ import { readFileSync } from 'fs'
 import { join } from 'path'
 import { SyntaxErrorInfo } from '../error'
 import { LocationRange } from '../location'
+import { firstTokens } from './locate'
 
 export const parserTokenNames = <const>[
     'program',
@@ -53,25 +54,29 @@ export type ParseBranch = TokenName[]
 const rawRules = JSON.parse(readFileSync(join(__dirname, '..', 'grammar.json')).toString()).rules
 export const rules: Map<ParserTokenName, Rule> = new Map(rawRules.map((r: Rule) => [r.name, r]))
 
+export const firstTokensMap: Map<ParserTokenName, Set<LexerTokenName>> =
+    new Map([...rules.keys()].map((n) => [<ParserTokenName>n, firstTokens(n)]))
+
 export const parse = (tokens: LexerToken[], node: TokenName = 'program'): Token | SyntaxErrorInfo => {
     const token = parseToken(tokens, node)
     if (token === true) {
-        return { tokenChain: [node], expected: [node], got: tokens[0].name, location: tokens[0].location }
+        return { expected: [node], got: tokens[0].name, location: tokens[0].location }
     }
     if ('expected' in token) {
         return token
     }
+    console.dir(compactToken(flattenToken(token)), { depth: null, colors: true, compact: true })
     if (tokenSize(token) === tokens.length - 1) {
         return token
     } else {
-        return { tokenChain: [node], expected: ['eof'], got: tokens[0].name, location: tokens[0].location }
+        const lastParsed = tokens[tokenSize(token)]
+        return { expected: ['eof'], got: lastParsed.name, location: lastParsed.location }
     }
 }
 
 export const parseToken = (tokens: LexerToken[],
                            node: TokenName = 'program',
-                           index: number = 0,
-                           tokenChain: TokenName[] = [node]
+                           index: number = 0
 ): Token | SyntaxErrorInfo | true => {
     const rule = rules.get(<ParserTokenName>node)!
     if (rule) {
@@ -79,7 +84,7 @@ export const parseToken = (tokens: LexerToken[],
         for (const branch of rule.branches) {
             if (isEmptyBranch(branch)) return true
             const transform = { name: <ParserTokenName>node, branch }
-            const branchToken = parseTransform(transform, tokens, index, tokenChain)
+            const branchToken = parseTransform(transform, tokens, index)
             if ('name' in branchToken) {
                 return branchToken
             } else {
@@ -91,7 +96,6 @@ export const parseToken = (tokens: LexerToken[],
         return syntaxError!
     } else {
         const error: SyntaxErrorInfo = {
-            tokenChain,
             expected: [node],
             got: tokens[index].name,
             location: tokens[index].location
@@ -103,11 +107,10 @@ export const parseToken = (tokens: LexerToken[],
 const parseTransform = (transform: Transform,
                         tokens: LexerToken[],
                         index: number,
-                        tokenChain: TokenName[]
 ): Token | SyntaxErrorInfo => {
     const nodes = []
     for (const branchTokenName of transform.branch) {
-        const branchToken = parseToken(tokens, branchTokenName, index, [...tokenChain, transform.name])
+        const branchToken = parseToken(tokens, branchTokenName, index)
         if (branchToken === true) continue
         if ('expected' in branchToken) return branchToken
         nodes.push(branchToken)