k&r 04-06: added variable support

k&r/04-funcs-and-prog-struct/04-calc.c

@@ -2,6 +2,8 @@
 #include <stdlib.h>
 #include <string.h>
 #include <math.h>
+#include <ctype.h> 
+#include <assert.h>
 
 /* --------- ERROR MESSAGES */
 #define printerr(format, ...) printf("error: " format "\n", ##__VA_ARGS__)
@@ -12,6 +14,7 @@
 #define EMPTY_STACK_ERR "stack empty" 
 #define SHORT_STACK_ERR "not enough elements on stack"
 #define UNKNOWN_TOKEN_ERR "unknown token %s"
+#define VAR_NOT_SET_ERR "variable %c has no value"
 
 /* --------- PROMPT FORMATS */
 #define PROMPT_F     ">> "
@@ -28,6 +31,7 @@
 int sp = 0;
 double val[MAXVAL];
 
+/* length: current length of stack */
 #define length() sp
 /* push: push f onto value stack */
 #define push(x) ((sp < MAXVAL) ? val[sp++] = (x) : printerr(FULL_STACK_ERR, ((double) (x))))
@@ -37,8 +41,6 @@ double val[MAXVAL];
 #define peek() (sp ? val[sp-1] : (printerr(EMPTY_STACK_ERR), 0))
 /* clear: clear stack */
 #define clear() (sp = 0)
-/* print_peek: print top element, leave stack unchanged */
-#define print_peek() printf(PEEK_PRINT_F, peek())
 /* dup: duplicate top element */
 #define dup() push(peek())
 /* swap: swap top two elements */
@@ -49,6 +51,38 @@ double val[MAXVAL];
         } \
    } while (0) 
 
+/* -------- STACK PRINTING FUNCTIONS */
+double lst_print;
+/* print_peek: print top element, leave stack unchanged */
+#define print_peek() printf(PEEK_PRINT_F, lst_print = peek())
+/* print_pop: pop top element and print it */
+#define print_pop() printf(POP_PRINT_F, lst_print = pop())
+
+/* ------- GLOBAL VARIABLE NAMESPACE */
+#define NS_SIZE ('z' - 'a' + 1)
+    
+char var_flags[NS_SIZE];
+double var_vals[NS_SIZE];
+
+/* set_var: pop val from stack, set variable c to val */
+#define set_var(c) \
+    do { \
+        int i = c - 'a'; \
+        var_flags[i] = 1; \
+        var_vals[i] = pop(); \
+    } while (0)
+
+/* get_var: push value of c to stack */
+#define get_var(c) \
+    do { \
+        int i = c - 'a'; \
+        if (!var_flags[i]) \
+            printerr(VAR_NOT_SET_ERR, i+'a'); \
+        else \
+            push(var_vals[i]); \
+    } while (0)
+
+
 /* --------- CALCULATOR FUNCTION TYPES */
 
 /* the following macros allow us to call native c constructs in a declarative style */
@@ -88,11 +122,13 @@ double val[MAXVAL];
 void help(void);
 
 #define COMMANDS \
+    X(_, "last printed value", CALL, lst_print, VALUE) \
+    X(ENTER, "pop top of stack and print it", CALL, print_pop, COMMAND) \
     X(print, "print top of stack", CALL, print_peek, COMMAND) \
     X(dup, "duplicate top of stack", COMMAND) \
     X(swap, "swap top two elements of stack", COMMAND) \
     X(clear, "clear stack", COMMAND) \
-    X(help, "print all available commands", COMMAND)
+    X(help, "print all available commands", COMMAND) \
 
 #define OPERATORS \
     X(+, "add operands", COMM_OP) \
@@ -103,7 +139,8 @@ void help(void);
     X(>, "greater than", NONC_OP, double) \
     X(<, "less than", NONC_OP, double) \
     X(<=, "less than or equal", NONC_OP, double) \
-    X(>=, "greater than or equal", NONC_OP, double)
+    X(>=, "greater than or equal", NONC_OP, double) \
+    X(==, "test equality", COMM_OP)
 
 #define MATH_H_BINDINGS \
     X(sin, "sine", UNARY_FUN) \
@@ -132,12 +169,19 @@ void help(void);
     OPERATORS \
     MATH_H_BINDINGS
 
+/* variable manipulation tokens */
+#define VAR_TOKENS \
+    X('=', "pop value top from stack and set %s to value", set_var) \
+    X('$', "push value of %s to top of stack", get_var)
+
+
 /* --------- MAIN PROGRAM */ 
 
 #define MAXTOKEN 100
 int gettoken(char *token, int max_t);
 char * parsef(char *s, double *x);
 
+
 /* reverse Polish calculator */
 int main()
 {
@@ -149,7 +193,7 @@ int main()
     while (t_len = gettoken(token, MAXTOKEN)) {
         if (t_len < 0) { /* newline token */
             if (length())
-                printf(POP_PRINT_F,  pop());
+                print_pop();
             printf(PROMPT_F);
         } else
     #define X(F, DESC, APPLY, ...) \
@@ -157,9 +201,15 @@ int main()
             APPLY(F, ##__VA_ARGS__); \
         else
         TOKENS
+    #undef X
+    #define X(C, DESC, F) \
+        if (t_len == 2 && token[0] == C && isalpha(token[1])) \
+            F(tolower(token[1])); \
+        else
+        VAR_TOKENS
     #undef X
         if (*parsef(token, &x) == '\0')
-            push(x);
+                    push(x);
         else
             printerr(UNKNOWN_TOKEN_ERR, token);
     }
@@ -171,21 +221,31 @@ int main()
     return 0;
 }
 
+/* ---------- HELP COMMAND */
+#define MAX_CMD_W 10 /* token padding */
+#define VAR_STR "X"  /* string to represent variable */
+
+/* we verify that no token is to large to be pretty printed */
+#define X(TOKEN, ...) \
+    static_assert(sizeof(#TOKEN) / sizeof(char) <= MAX_CMD_W, \
+        "size of " #TOKEN " is to large for pretty printing " \
+        "in help command");
+    TOKENS
+#undef X
 
-#define COMMAND_W "10"
-#define NEWLINE_DESC "pop top of stack and print it"
 /* help: prints all available calculator functions */
 void help(void)
 {
-    printf("%-" COMMAND_W "s" NEWLINE_DESC "\n", "ENTER");
-#define X(F, DESC, ...) printf("%-" COMMAND_W "s" DESC "\n", #F);
+#define X(C, DESC, ...) \
+    printf("%c%-*s" DESC "\n", C, MAX_CMD_W-1, VAR_STR, VAR_STR);
+    VAR_TOKENS
+#undef X
+#define X(F, DESC, ...) printf("%-*s" DESC "\n", MAX_CMD_W, #F);
     TOKENS
 #undef X
 }
 
 /* -------- PARSING FUNCTIONS */
-#include <ctype.h> 
-
 #define BLANK ' '
 
 /* gettoken: get next space delimited token from input