diff --git a/Cargo.lock b/Cargo.lock
index 48a3dac..ff31497 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,9 +2,9 @@
 # It is not intended for manual editing.
 [[package]]
 name = "aho-corasick"
-version = "0.7.10"
+version = "0.7.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8716408b8bc624ed7f65d223ddb9ac2d044c0547b6fa4b0d554f3a9540496ada"
+checksum = "7404febffaa47dac81aa44dba71523c9d069b1bdc50a77db41195149e17f68e5"
 dependencies = [
  "memchr",
 ]
@@ -18,58 +18,23 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "arrayref"
-version = "0.3.6"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a4c527152e37cf757a3f78aae5a06fbeefdb07ccc535c980a3208ee3060dd544"
-
-[[package]]
-name = "arrayvec"
-version = "0.5.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cff77d8686867eceff3105329d4698d96c2391c176d5d03adc90c7389162b5b8"
-
-[[package]]
-name = "autocfg"
-version = "1.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f8aac770f1885fd7e387acedd76065302551364496e46b3dd00860b2f8359b9d"
-
 [[package]]
 name = "az"
 version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e9bcd47d94aa4eb8c076b50fc61a75020789394ffb9bd74a180b3379130f6569"
 
-[[package]]
-name = "base64"
-version = "0.11.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b41b7ea54a0c9d92199de89e20e58d49f02f8e699814ef3fdf266f6f748d15c7"
-
 [[package]]
 name = "bitflags"
 version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
-[[package]]
-name = "blake2b_simd"
-version = "0.5.10"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8fb2d74254a3a0b5cac33ac9f8ed0e44aa50378d9dbb2e5d83bd21ed1dc2c8a"
-dependencies = [
- "arrayref",
- "arrayvec",
- "constant_time_eq",
-]
-
 [[package]]
 name = "cc"
-version = "1.0.54"
+version = "1.0.66"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7bbb73db36c1246e9034e307d0fba23f9a2e251faa47ade70c1bd252220c8311"
+checksum = "4c0496836a84f8d0495758516b8621a622beb77c0fed418570e50764093ced48"
 
 [[package]]
 name = "cfg-if"
@@ -78,37 +43,26 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4785bdd1c96b2a846b2bd7cc02e86b6b3dbf14e7e53446c4f54c92a361040822"
 
 [[package]]
-name = "constant_time_eq"
-version = "0.1.5"
+name = "cfg-if"
+version = "1.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "245097e9a4535ee1e3e3931fcfcd55a796a44c643e8596ff6566d68f09b87bbc"
-
-[[package]]
-name = "crossbeam-utils"
-version = "0.7.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3c7c73a2d1e9fc0886a08b93e98eb643461230d5f1925e4036204d5f2e261a8"
-dependencies = [
- "autocfg",
- "cfg-if",
- "lazy_static",
-]
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "dirs-next"
-version = "1.0.1"
+version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1cbcf9241d9e8d106295bd496bbe2e9cffd5fa098f2a8c9e2bbcbf09773c11a8"
+checksum = "cf36e65a80337bea855cd4ef9b8401ffce06a7baedf2e85ec467b1ac3f6e82b6"
 dependencies = [
- "cfg-if",
+ "cfg-if 1.0.0",
  "dirs-sys-next",
 ]
 
 [[package]]
 name = "dirs-sys-next"
-version = "0.1.0"
+version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c60f7b8a8953926148223260454befb50c751d3c50e1c178c4fd1ace4083c9a"
+checksum = "99de365f605554ae33f115102a02057d4fc18b01f3284d6870be0938743cfe7d"
 dependencies = [
  "libc",
  "redox_users",
@@ -117,20 +71,20 @@ dependencies = [
 
 [[package]]
 name = "getrandom"
-version = "0.1.14"
+version = "0.1.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7abc8dd8451921606d809ba32e95b6111925cd2906060d2dcc29c070220503eb"
+checksum = "fc587bc0ec293155d5bfa6b9891ec18a1e330c234f896ea47fbada4cadbe47e6"
 dependencies = [
- "cfg-if",
+ "cfg-if 0.1.10",
  "libc",
  "wasi",
 ]
 
 [[package]]
 name = "gmp-mpfr-sys"
-version = "1.2.4"
+version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e2a3da028fc357b7a48a9dd11966fd036965ca4fe56c1588918dcd06f46eeb4e"
+checksum = "a57fdb339d49833021b1fded600ed240ae907e33909d5511a61dff884df7f16e"
 dependencies = [
  "libc",
  "winapi",
@@ -166,36 +120,35 @@ checksum = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
 
 [[package]]
 name = "libc"
-version = "0.2.71"
+version = "0.2.81"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9457b06509d27052635f90d6466700c65095fdf75409b3fbdd903e988b886f49"
+checksum = "1482821306169ec4d07f6aca392a4681f66c75c9918aa49641a2595db64053cb"
 
 [[package]]
 name = "log"
-version = "0.4.8"
+version = "0.4.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "14b6052be84e6b71ab17edffc2eeabf5c2c3ae1fdb464aae35ac50c67a44e1f7"
+checksum = "4fabed175da42fed1fa0746b0ea71f412aa9d35e76e95e59b192c64b9dc2bf8b"
 dependencies = [
- "cfg-if",
+ "cfg-if 0.1.10",
 ]
 
 [[package]]
 name = "memchr"
-version = "2.3.3"
+version = "2.3.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3728d817d99e5ac407411fa471ff9800a778d88a24685968b36824eaf4bee400"
+checksum = "0ee1c47aaa256ecabcaea351eae4a9b01ef39ed810004e298d2511ed284b1525"
 
 [[package]]
 name = "nix"
-version = "0.17.0"
+version = "0.18.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "50e4785f2c3b7589a0d0c1dd60285e1188adac4006e8abd6dd578e1567027363"
+checksum = "83450fe6a6142ddd95fb064b746083fc4ef1705fe81f64a64e1d4b39f54a1055"
 dependencies = [
  "bitflags",
  "cc",
- "cfg-if",
+ "cfg-if 0.1.10",
  "libc",
- "void",
 ]
 
 [[package]]
@@ -244,21 +197,21 @@ dependencies = [
 
 [[package]]
 name = "ppv-lite86"
-version = "0.2.8"
+version = "0.2.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "237a5ed80e274dbc66f86bd59c1e25edc039660be53194b5fe0a482e0f2612ea"
+checksum = "ac74c624d6b2d21f425f752262f42188365d7b8ff1aff74c82e45136510a4857"
 
 [[package]]
 name = "proc-macro-hack"
-version = "0.5.16"
+version = "0.5.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "7e0456befd48169b9f13ef0f0ad46d492cf9d2dbb918bcf38e01eed4ce3ec5e4"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
 
 [[package]]
 name = "proc-macro2"
-version = "1.0.18"
+version = "1.0.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "beae6331a816b1f65d04c45b078fd8e6c93e8071771f41b8163255bbd8d7c8fa"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
 dependencies = [
  "unicode-xid",
 ]
@@ -325,26 +278,25 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.1.56"
+version = "0.1.57"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2439c63f3f6139d1b57529d16bc3b8bb855230c8efcc5d3a896c8bea7c3b1e84"
+checksum = "41cc0f7e4d5d4544e8861606a285bb08d3e70712ccc7d2b84d7c0ccfaf4b05ce"
 
 [[package]]
 name = "redox_users"
-version = "0.3.4"
+version = "0.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "09b23093265f8d200fa7b4c2c76297f47e681c655f6f1285a8780d6a022f7431"
+checksum = "de0737333e7a9502c789a36d7c7fa6092a49895d4faa31ca5df163857ded2e9d"
 dependencies = [
  "getrandom",
  "redox_syscall",
- "rust-argon2",
 ]
 
 [[package]]
 name = "regex"
-version = "1.3.9"
+version = "1.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c3780fcf44b193bc4d09f36d2a3c87b251da4a046c87795a0d35f4f927ad8e6"
+checksum = "38cf2c13ed4745de91a5eb834e11c00bcc3709e773173b2ce4c56c9fbde04b9c"
 dependencies = [
  "aho-corasick",
  "memchr",
@@ -354,40 +306,28 @@ dependencies = [
 
 [[package]]
 name = "regex-syntax"
-version = "0.6.18"
+version = "0.6.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "26412eb97c6b088a6997e05f69403a802a92d520de2f8e63c2b65f9e0f47c4e8"
+checksum = "3b181ba2dcf07aaccad5448e8ead58db5b742cf85dfe035e2227f137a539a189"
 
 [[package]]
 name = "rug"
-version = "1.9.0"
+version = "1.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a6cfccfa888f22369385e0fc5f37a37fca05782fc653df5fe7de0934cbe66632"
+checksum = "e538d00da450a8e48aac7e6322e67b2dc86ec71a1feeac0e3954c4f07f01bc45"
 dependencies = [
  "az",
  "gmp-mpfr-sys",
  "libc",
 ]
 
-[[package]]
-name = "rust-argon2"
-version = "0.7.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2bc8af4bda8e1ff4932523b94d3dd20ee30a87232323eda55903ffd71d2fb017"
-dependencies = [
- "base64",
- "blake2b_simd",
- "constant_time_eq",
- "crossbeam-utils",
-]
-
 [[package]]
 name = "rustyline"
-version = "6.2.0"
+version = "6.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3358c21cbbc1a751892528db4e1de4b7a2b6a73f001e215aaba97d712cfa9777"
+checksum = "6f0d5e7b0219a3eadd5439498525d4765c59b7c993ef0c12244865cd2d988413"
 dependencies = [
- "cfg-if",
+ "cfg-if 0.1.10",
  "dirs-next",
  "libc",
  "log",
@@ -414,9 +354,9 @@ checksum = "fa8f3741c7372e75519bd9346068370c9cdaabcc1f9599cbcf2a2719352286b7"
 
 [[package]]
 name = "syn"
-version = "1.0.31"
+version = "1.0.54"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b5304cfdf27365b7585c25d4af91b35016ed21ef88f17ced89c7093b43dba8b6"
+checksum = "9a2af957a63d6bd42255c359c93d9bfdb97076bd3b820897ce55ffbfbf107f44"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -446,21 +386,21 @@ dependencies = [
 
 [[package]]
 name = "unicode-segmentation"
-version = "1.6.0"
+version = "1.7.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e83e153d1053cbb5a118eeff7fd5be06ed99153f00dbcd8ae310c5fb2b22edc0"
+checksum = "bb0d2e7be6ae3a5fa87eed5fb451aff96f2573d2694942e40543ae0bbe19c796"
 
 [[package]]
 name = "unicode-width"
-version = "0.1.7"
+version = "0.1.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "caaa9d531767d1ff2150b9332433f32a24622147e5ebb1f26409d5da67afd479"
+checksum = "9337591893a19b88d8d87f2cec1e73fad5cdfd10e5a6f349f498ad6ea2ffb1e3"
 
 [[package]]
 name = "unicode-xid"
-version = "0.2.0"
+version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
 
 [[package]]
 name = "utf8parse"
@@ -474,12 +414,6 @@ version = "0.9.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b5a972e5669d67ba988ce3dc826706fb0a8b01471c088cb0b6110b805cc36aed"
 
-[[package]]
-name = "void"
-version = "1.0.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "6a02e4885ed3bc0f2de90ea6dd45ebcbb66dacffe03547fadbb0eeae2770887d"
-
 [[package]]
 name = "wasi"
 version = "0.9.0+wasi-snapshot-preview1"
@@ -488,9 +422,9 @@ checksum = "cccddf32554fecc6acb585f82a32a72e28b48f8c4c1883ddfeeeaa96f7d8e519"
 
 [[package]]
 name = "winapi"
-version = "0.3.8"
+version = "0.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8093091eeb260906a183e6ae1abdba2ef5ef2257a21801128899c3fc699229c6"
+checksum = "5c839a674fcd7a98952e593242ea400abe93992746761e38641405d28b00f419"
 dependencies = [
  "winapi-i686-pc-windows-gnu",
  "winapi-x86_64-pc-windows-gnu",
diff --git a/kalk/Cargo.toml b/kalk/Cargo.toml
index e331d8c..7e15a94 100644
--- a/kalk/Cargo.toml
+++ b/kalk/Cargo.toml
@@ -12,7 +12,7 @@ categories = ["mathematics", "parser-implementations"]
 
 [dependencies]
 phf = { version = "0.8", features = ["macros"] }
-rug = "1.9.0"
+rug = "1.11.0"
 test-case = "1.0.0"
 regex = "1"
 lazy_static = "1.4.0"
diff --git a/kalk/src/lexer.rs b/kalk/src/lexer.rs
index b0bee1e..be0ef66 100644
--- a/kalk/src/lexer.rs
+++ b/kalk/src/lexer.rs
@@ -67,18 +67,23 @@ impl<'a> Lexer<'a> {
     }
 
     fn next(&mut self) -> Token {
+        let eof = build(TokenKind::EOF, "", (self.index, self.index));
         let mut c = if let Some(c) = self.peek() {
             *c
         } else {
-            return build(TokenKind::EOF, "", (self.index, self.index));
+            return eof;
         };
 
         while c == ' ' || c == '\t' || c == '\r' || c == '\n' {
             if let None = self.advance() {
-                return build(TokenKind::EOF, "", (self.index, self.index));
+                return eof;
             }
 
-            c = *self.peek().unwrap();
+            c = if let Some(c) = self.peek() {
+                *c
+            } else {
+                return eof;
+            }
         }
 
         if c.is_digit(10) {
@@ -244,6 +249,24 @@ mod tests {
         match_tokens(tokens, expected);
     }
 
+    #[test]
+    fn test_empty() {
+        // test_case macro doesn't seem to work with spaces.
+        let test_cases = vec![" ", "     ", "test ", " test     "];
+
+        for input in test_cases {
+            let tokens = Lexer::lex(input);
+
+            if regex::Regex::new(r"^\s*$").unwrap().is_match(input) {
+                let expected = vec![TokenKind::EOF];
+                match_tokens(tokens, expected);
+            } else {
+                let expected = vec![TokenKind::Identifier, TokenKind::EOF];
+                match_tokens(tokens, expected);
+            }
+        }
+    }
+
     #[test_case("1")]
     #[test_case("24")]
     #[test_case("56.4")]