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Lexer pretty error; parser refactoring
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,50 @@ | ||
import { LexerTokenName } from '../lexer/lexer' | ||
import { ParseBranch, ParserTokenName, rules, TokenName, Transform } from './parser' | ||
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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]) | ||
} | ||
} | ||
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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 | ||
} | ||
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const canMatchEmpty = (token: TokenName): boolean => { | ||
const rule = rules.get(<ParserTokenName>token) | ||
if (rule) { | ||
return rule.branches.some(b => branchCanMatchEmpty(b)) | ||
} else { | ||
return token === 'e' | ||
} | ||
} | ||
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const branchCanMatchEmpty = (branch: ParseBranch): boolean => { | ||
for (let t of branch) { | ||
if (!canMatchEmpty(t)) { | ||
return false | ||
} | ||
} | ||
return true | ||
} |
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