Scheme: Improved lambda parameter (PrismJS#2346)

components/prism-racket.js

@@ -1,4 +1,11 @@
-Prism.languages.racket = Prism.languages.extend('scheme', {});
+Prism.languages.racket = Prism.languages.extend('scheme', {
+	'lambda-parameter': {
+		// the racket lambda syntax is a lot more complex, so we won't even attempt to capture it.
+		// this will just prevent false positives of the `function` pattern
+		pattern: /(\(lambda\s+\()[^()'\s]+/,
+		lookbehind: true
+	}
+});
 
 // Add brackets to racket
 // The basic idea here is to go through all pattens of Scheme and replace all occurrences of "(" with the union of "("

components/prism-scheme.js

@@ -13,10 +13,17 @@ Prism.languages.scheme = {
 		greedy: true,
 		alias: 'string'
 	},
-	'lambda-parameter': {
-		pattern: /(\(lambda\s+\()[^()'\s]+/,
-		lookbehind: true
-	},
+	'lambda-parameter': [
+		// https://www.cs.cmu.edu/Groups/AI/html/r4rs/r4rs_6.html#SEC30
+		{
+			pattern: /(\(lambda\s+)[^()'\s]+/,
+			lookbehind: true
+		},
+		{
+			pattern: /(\(lambda\s+\()[^()']+/,
+			lookbehind: true
+		}
+	],
 	'keyword': {
 		pattern: /(\()(?:define(?:-library|-macro|-syntax|-values)?|defmacro|(?:case-)?lambda|let(?:(?:\*|rec)?(?:-values)?|-syntax|rec-syntax)|else|if|cond|begin|delay(?:-force)?|parameterize|guard|set!|(?:quasi-)?quote|syntax-(?:case|rules))(?=[()\s]|$)/,
 		lookbehind: true

tests/languages/scheme/lambda_parameter_feature.test

@@ -1,13 +1,26 @@
+(lambda x x)
+(lambda (x) x)
 (lambda (foo bar) (concat foo bar))
 
 ----------------------------------------------------
 
 [
+	["punctuation", "("],
+	["keyword", "lambda"],
+	["lambda-parameter", "x"],
+	" x",
+	["punctuation", ")"],
+	["punctuation", "("],
+	["keyword", "lambda"],
+	["punctuation", "("],
+	["lambda-parameter", "x"],
+	["punctuation", ")"],
+	" x",
+	["punctuation", ")"],
 	["punctuation", "("],
 	["keyword", "lambda"],
 	["punctuation", "("],
-	["lambda-parameter", "foo"],
-	" bar",
+	["lambda-parameter", "foo bar"],
 	["punctuation", ")"],
 	["punctuation", "("],
 	["function", "concat"],