Add lexer example

Makefile

@@ -2,7 +2,7 @@ build/counter: examples/counter.c coroutine.h build/coroutine.a
 	gcc -I. -Wall -Wextra -ggdb -o build/counter examples/counter.c build/coroutine.a
 
 .PHONY: examples
-examples: build/counter build/counter_cpp build/counter_c3 build/counter_jai build/echo
+examples: build/counter build/counter_cpp build/counter_c3 build/counter_jai build/echo build/lexer
 
 build/echo: examples/echo.c3 coroutine.c3 build/coroutine.a
 	c3c compile -l build/coroutine.a -o build/echo examples/echo.c3 coroutine.c3
@@ -16,6 +16,9 @@ build/counter_c3: examples/counter.c3 coroutine.c3 build/coroutine.a
 build/counter_jai: examples/counter.jai build/coroutine.a build/coroutine.so
 	jai-linux examples/counter.jai
 
+build/lexer: examples/lexer.c coroutine.h build/coroutine.a
+	gcc -I. -Wall -Wextra -ggdb -o build/lexer examples/lexer.c build/coroutine.a
+
 build/coroutine.so: coroutine.c
 	mkdir -p build
 	gcc -Wall -Wextra -ggdb -shared -fPIC -o build/coroutine.so coroutine.c

examples/lexer.c

@@ -0,0 +1,85 @@
+// Lexer is a classical example of usecase for coroutines.
+// This is a *very* simple and basic lexer that
+// can lex single digit integers, + and -.
+// The example would be better if we could return values
+// when we yield (kind of like a generator). But it is what it is.
+
+#include <stdio.h>
+#include <assert.h>
+#include <stdbool.h>
+
+#include <coroutine.h>
+
+typedef enum {
+    TK_INT,
+    TK_OP,
+    TK_EOF
+} TokenKind;
+
+typedef union {
+    char tk_op;
+    int  tk_int;
+} TokenValue;
+
+TokenKind  token_kind  = TK_EOF;
+TokenValue token_value = {0};
+
+void lex(void* input_void) {
+    if (input_void == NULL) return;
+
+    const char* input = input_void;
+
+    while(true) {
+        switch(*input) {
+            // Numba
+            case '0': case '1': case '2': case '3': case '4':
+            case '5': case '6': case '7': case '8': case '9': {
+                token_kind = TK_INT;
+                token_value.tk_int = *input - '0';
+            } break;
+
+            // Operators
+            case '+': case '-': {
+                token_kind = TK_OP;
+                token_value.tk_op = *input;
+            } break;
+
+            default: {
+                token_kind = TK_EOF;
+                return;
+            }
+        }
+        input++;
+
+        // For every token we consume, we yield control back to the caller (a parser, I guess).
+        coroutine_yield();
+    }
+}
+
+int main(int argc, char* argv[]){
+    if (argc != 2) {
+        printf("Usage: %s <input-text>\n", argv[0]);
+        return 1;
+    }
+
+    coroutine_init();
+    {
+        coroutine_go(lex, argv[1]);
+
+        // Consume those tokens
+        bool quit = false;
+        while(!quit && coroutine_alive() > 1){
+            // Yield control to the lexer.
+            // It will lex and yield control back to here.
+            coroutine_yield();
+            switch(token_kind){
+                case TK_INT: { printf("TK_INT: %d\n", token_value.tk_int); } break;
+                case TK_OP:  { printf("TK_OP:  %c\n", token_value.tk_op); } break;
+                default:     { printf("Done!\n"); quit = true; } break;
+            }
+        }
+    }
+    coroutine_finish();
+
+    return 0;
+}