From e01cb693bc5737792e2b37abfd98d2d8f81bac4d Mon Sep 17 00:00:00 2001
From: Akshay Nair <phenax5@gmail.com>
Date: Thu, 10 Aug 2023 22:45:00 +0530
Subject: feat: adds simple evaluator

---
 src/parser.ts | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 src/parser.ts

(limited to 'src/parser.ts')

diff --git a/src/parser.ts b/src/parser.ts
new file mode 100644
index 0000000..1c5c08f
--- /dev/null
+++ b/src/parser.ts
@@ -0,0 +1,66 @@
+import { Enum, constructors, match } from './utils/adt'
+import * as P from './utils/parser-comb'
+
+export type Expr = Enum<{
+  Call: { name: string; args: Expr[] }
+  Identifier: string
+  VarIdentifier: string
+  LiteralString: string
+}>
+
+export const Expr = constructors<Expr>()
+
+const whitespace = P.regex(/^\s*/)
+const consumeWhitespace = <A>(p: P.Parser<A>): P.Parser<A> =>
+  P.between(whitespace, p, whitespace)
+const comma = consumeWhitespace(P.string(','))
+const parens = <A>(p: P.Parser<A>): P.Parser<A> =>
+  P.between(P.string('('), p, P.string(')'))
+const identifierParser = P.regex(/^[a-z][a-z0-9_-]*/i)
+const varIdentifierParser = P.regex(/^--[a-z][a-z0-9-]*/i)
+const singleQuote = P.string("'")
+const doubleQuote = P.string('"')
+
+const identifierExprParser = P.map(identifierParser, Expr.Identifier)
+const varIdentifierExprParser = P.map(varIdentifierParser, Expr.VarIdentifier)
+
+const callExprParser = (input: string) =>
+  P.map(
+    P.zip2(
+      consumeWhitespace(identifierParser),
+      parens(consumeWhitespace(P.sepBy(exprParser, comma)))
+    ),
+    ([name, args]) => Expr.Call({ name, args })
+  )(input)
+
+const stringLiteralParser: P.Parser<Expr> = P.map(
+  P.or([
+    P.between(singleQuote, P.regex(/^[^']*/), singleQuote),
+    P.between(doubleQuote, P.regex(/^[^"]*/), doubleQuote),
+  ]),
+  Expr.LiteralString
+)
+
+const exprParser: P.Parser<Expr> = P.or([
+  stringLiteralParser,
+  varIdentifierExprParser,
+  callExprParser,
+  identifierExprParser,
+])
+
+const multiExprParser = P.many1(exprParser)
+
+export const parse = (input: string): Array<Expr> => {
+  const res = multiExprParser(input.trim())
+  return match(res, {
+    Ok: ({ value, input }) => {
+      if (input) {
+        throw new Error(`Input not consumed completely here brosky: "${input}"`)
+      }
+      return value
+    },
+    Err: ({ error, input }) => {
+      throw new Error(`${error}.\n Left input: ${input.slice(0, 20)}...`)
+    },
+  })
+}
-- 
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