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parser.ts
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parser.ts
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import * as Types from './types';
type TokenHandler = (ctx: ParseContext) => void;
interface ParseContext {
source: string;
i: number;
head: Types.Expr[];
stack: Types.Expr[][];
acc: string;
}
const openParen = (ctx: ParseContext): void => {
if (!ctx.head) {
const around = ctx.source.substring(Math.max(0, ctx.i - 20), ctx.i + 20);
throw new Error(`Unexpected '(' at position ${ctx.i} (stack empty): ...${around}...`);
}
const temp: Types.Expr[] = [];
ctx.head.push(temp);
ctx.stack.push(ctx.head);
ctx.head = temp;
};
const closeParen = (ctx: ParseContext): void => {
flushToken(ctx);
if (ctx.stack.length === 0) {
const around = ctx.source.substring(Math.max(0, ctx.i - 20), ctx.i + 20);
throw new Error(`Unmatched ')' at position ${ctx.i}: ...${around}...`);
}
ctx.head = ctx.stack.pop()!;
};
const flushToken = (ctx: ParseContext): void => {
const token = ctx.acc;
ctx.acc = '';
if (!token) return;
if (!ctx.head.length) ctx.head.push(Types.Leaf.apply(token));
else if (/^-?\d+(\.\d+)?$/.test(token)) ctx.head.push(Types.Leaf.atom(Number(token)));
else ctx.head.push(Types.Leaf.word(token));
};
const parseString = (ctx: ParseContext): void => {
let str = '';
const escapes: Record<string, string> = { n: '\n', t: '\t', '\\': '\\', '"': '"' };
while (++ctx.i < ctx.source.length && ctx.source[ctx.i] !== '"') {
if (ctx.source[ctx.i] === '\\' && ctx.i + 1 < ctx.source.length) {
const next = ctx.source[++ctx.i];
str += escapes[next] ?? '\\' + next;
} else str += ctx.source[ctx.i];
}
ctx.head.push(Types.Leaf.string(str));
};
const skipComment = (ctx: ParseContext): void => {
flushToken(ctx);
while (ctx.i < ctx.source.length && ctx.source[ctx.i] !== '\n') ctx.i++;
};
const tokenTable: Record<string, TokenHandler> = {
'"': parseString,
'(': openParen,
')': closeParen,
';': skipComment,
' ': flushToken,
'\n': flushToken,
'\r': flushToken,
'\t': flushToken
};
export function parse(source: string): Types.Expr {
const tree: Types.Expr[] = [];
const ctx: ParseContext = {
source,
i: 0,
head: tree,
stack: [tree],
acc: ''
};
for (; ctx.i < source.length; ctx.i++) {
const handler = tokenTable[source[ctx.i]];
if (handler) handler(ctx);
else ctx.acc += source[ctx.i];
}
return tree[0];
}

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