3 files changed, 27 insertions, 20 deletions
diff --git a/src/interpreter/PeggyParser.js b/src/interpreter/PeggyParser.js
index 5671d91..632f1b7 100644
--- a/src/interpreter/PeggyParser.js
+++ b/src/interpreter/PeggyParser.js
@@ -201,7 +201,7 @@ export default (function () {
     );
   };
 
-  function peg$parse(input, options) {
+  function peg$parse(input, options, allowUnderscores = false) {
     options = options !== undefined ? options : {};
 
     var peg$FAILED = {};
@@ -215,7 +215,7 @@ export default (function () {
     var peg$c2 = ".";
     var peg$c3 = "\r\n";
 
-    var peg$r0 = /^[a-zA-Z0-9]/;
+    var peg$r0 = allowUnderscores ? /^[a-zA-Z0-9]_/ : /^[a-zA-Z0-9]/;
     var peg$r1 = /^[\\\u03BB]/;
     var peg$r2 = /^[\t-\n ]/;
 
diff --git a/src/interpreter/interpreter.ts b/src/interpreter/interpreter.ts
index 0b3ae34..4599c46 100644
--- a/src/interpreter/interpreter.ts
+++ b/src/interpreter/interpreter.ts
@@ -198,22 +198,6 @@ export const betaReduce = (
   );
 };
 
-export const interpret = (term: string): DebrujinifiedLambdaTerm => {
-  const ast = parse(term);
-  const symbolTable = new SymbolTable();
-  const debrujined = debrujinify(ast, symbolTable);
-
-  let prev = debrujined;
-  let next = betaReduce(prev);
-
-  while (emitDebrujin(prev) !== emitDebrujin(next)) {
-    // alpha equivalence
-    prev = next;
-    next = betaReduce(prev);
-  }
-  return next;
-};
-
 export const emitDebrujin = (term: DebrujinifiedLambdaTerm): string => {
   if ("index" in term) {
     return term.index.toString();
@@ -253,3 +237,22 @@ export const emitNamed = (term: DebrujinifiedLambdaTerm): string => {
 
   throw new InvalidLambdaTermError(`Invalid lambda term: ${term}`);
 };
+
+export const interpret = (
+  term: string,
+  symbolTable = new SymbolTable(),
+  allowUnderscores = false,
+): DebrujinifiedLambdaTerm => {
+  const ast = parse(term, allowUnderscores);
+  const debrujined = debrujinify(ast, symbolTable);
+
+  let prev = debrujined;
+  let next = betaReduce(prev);
+
+  while (emitDebrujin(prev) !== emitDebrujin(next)) {
+    // alpha equivalence
+    prev = next;
+    next = betaReduce(prev);
+  }
+  return next;
+};
diff --git a/src/interpreter/parser.ts b/src/interpreter/parser.ts
index 5e3be0f..d288815 100644
--- a/src/interpreter/parser.ts
+++ b/src/interpreter/parser.ts
@@ -30,6 +30,10 @@ export const isVariable = (term: LambdaTerm): term is Variable => {
   return typeof term === "string";
 };
 
-export const parse = (term: string, library = false) => {
-  return peggyParser.parse(term, { peg$library: library });
+export const parse = (
+  term: string,
+  allowUnderscores = false,
+  library = false,
+) => {
+  return peggyParser.parse(term, { peg$library: library }, allowUnderscores);
 };