Add functions for unit displacements in the siz cardinal directions

This change is the "easy" part of #64, but to reduce the amount of duplicated
   code, this change also modifies the internals of implementing a function.
   The function identifier is now passed to the implementation as well, allowing
   many implementations of similar functions to be collapsed more easily.

doc/teapot.lyx

@@ -5900,7 +5900,65 @@ env
 \series default
 evaluates to the contents of the specified environment variable.
  If the variable does not exist, then an empty string will be returned.
+\end_layout
 
+\begin_layout Description
+above|below|left|right|up|down
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] As bare words (without any arguments and also without the parentheses)
+ these symbols return a one-cell displacement in the named direction, e.g.
+ 
+\family sans
+\series bold
+D
+\series default
+(above) 
+\family default
+\series medium
+gives the location of the same cell as the current on but in the previous
+ layer and 
+\family sans
+\series bold
+R
+\series default
+(up)
+\family default
+\series medium
+ yields the value of the cell one up from the current cell.
+ With parentheses, they act like 
+\series bold
+@
+\series default
+()
+\series medium
+ but displaced by one cell in the named direction, so 
+\family sans
+\series default
+right()
+\family default
+\series medium
+ returns the value of the cell immediately to the right of the current one,
+ and 
+\family sans
+\series default
+down(MYTABLE)
+\family default
+\series medium
+ gives the value one line down from the cell labeled 
+\family sans
+\series default
+MYTABLE
+\family default
+\series medium
+, etc.
 \end_layout
 
 \begin_layout Description
@@ -6153,6 +6211,30 @@ x
  is given in radians.
 \end_layout
 
+\begin_layout Description
+below
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] displacement by one cell in the positive 
+\series default
+\emph on
+z
+\emph default
+ direction; see the fuller description at 
+\family sans
+\series bold
+above
+\series default
+.
+\end_layout
+
 \begin_layout Description
 
 \series medium
@@ -6385,6 +6467,30 @@ x
  
 \end_layout
 
+\begin_layout Description
+down
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] displacement by one cell in the positive 
+\series default
+\emph on
+y
+\emph default
+ direction; see the fuller description at 
+\family sans
+\series bold
+above
+\series default
+.
+\end_layout
+
 \begin_layout Description
 
 \series medium
@@ -6809,6 +6915,30 @@ trunc
  value is returned.
 \end_layout
 
+\begin_layout Description
+left
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] displacement by one cell in the negative 
+\series default
+\emph on
+x
+\emph default
+ direction; see the fuller description at 
+\family sans
+\series bold
+above
+\series default
+.
+\end_layout
+
 \begin_layout Description
 
 \series medium
@@ -7248,6 +7378,30 @@ x
  
 \end_layout
 
+\begin_layout Description
+right
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] displacement by one cell in the positive 
+\series default
+\emph on
+x
+\emph default
+ direction; see the fuller description at 
+\family sans
+\series bold
+above
+\series default
+.
+\end_layout
+
 \begin_layout Description
 
 \series medium
@@ -7882,6 +8036,23 @@ x
 ).
 \end_layout
 
+\begin_layout Description
+up
+\series medium
+[([location
+\emph on
+
+\begin_inset space ~
+\end_inset
+
+l
+\emph default
+])] displacement by one cell in the negative 
+\series default
+\emph on
+y
+\end_layout
+
 \begin_layout Description
 
 \series medium
@@ -8405,28 +8576,61 @@ func
  – in the former case it receives an argument count of 0, and in the latter
  an argument count of -1.
  So the same symbol can have different semantics depending on which way
- it is called, but in most cases that would probably be counterintuitive.
- The no-parentheses form is useful, however, for constants like 
+ it is called.
+ In most cases such a difference is counterintuitive, but it seems to work
+ fairly well for the directional 
 \begin_inset Quotes eld
 \end_inset
 
-e,
+constants,
 \begin_inset Quotes erd
 \end_inset
 
- and it is also used to allow, for example, the names of the functions 
+ i.e.
+ bare 
 \begin_inset Quotes eld
 \end_inset
 
-floor, 
-\begin_inset Quotes eld
-\end_inset
-
-round,
+left
 \begin_inset Quotes erd
 \end_inset
 
- etc.
+ is the displacement &(-1,0,0), whereas left() is the location one to the
+ left.
+ The no-parentheses form is also useful for constants like 
+\begin_inset Quotes eld
+\end_inset
+
+e
+\begin_inset Quotes erd
+\end_inset
+
+ and 
+\begin_inset Quotes eld
+\end_inset
+
+tau
+\begin_inset Quotes erd
+\end_inset
+
+, and it is also used, for example, to allow the names of the functions
+ 
+\begin_inset Quotes eld
+\end_inset
+
+floor
+\begin_inset Quotes erd
+\end_inset
+
+, 
+\begin_inset Quotes eld
+\end_inset
+
+round
+\begin_inset Quotes erd
+\end_inset
+
+, etc.
  to be used as keywords for the int() function.
 \end_layout
 

src/common/eval.c

@@ -513,12 +513,28 @@ Token tmul(Token l, Token r)
     else result.u.flt = l.u.flt * ((FltT)r.u.integer);
   }
   /*}}}*/
+  else if ((l.type == EMPTY && r.type == LOCATION)
+	   || (l.type == LOCATION && r.type == EMPTY))
+    /* result is 0 location */ /*{{{*/
+  {
+    result.type = LOCATION;
+    OLOCATION(result.u.location);
+  }
+  /*}}}*/
   else if (l.type == LOCATION && r.type == INT)
   /* result is each component of location times right */ /*{{{*/
   {
     result.type = LOCATION;
-    for (size_t len = 0; len < 3; ++len)
-      result.u.location[len] = l.u.location[len] * r.u.integer;
+    for (Dimensions dim = X; dim < HYPER; ++dim)
+      result.u.location[dim] = l.u.location[dim] * r.u.integer;
+  }
+  /*}}}*/
+  else if (l.type == INT && r.type == LOCATION)
+  /* result is each component of right location times left */ /*{{{*/
+  {
+    result.type = LOCATION;
+    for (Dimensions dim = X; dim < HYPER; ++dim)
+      result.u.location[dim] = l.u.integer * r.u.location[dim];
   }
   /*}}}*/
   else if (l.type == LOCATION && r.type == LOCATION)
@@ -526,8 +542,8 @@ Token tmul(Token l, Token r)
   {
     result.type = INT;
     result.u.integer = 0;
-    for (size_t len = 0; len < 3; ++len)
-      result.u.integer += l.u.location[len] * r.u.location[len];
+    for (Dimensions dim = X; dim < HYPER; ++dim)
+      result.u.integer += l.u.location[dim] * r.u.location[dim];
   }
   /*}}}*/
   else if ((l.type == INT && r.type == STRING)
@@ -681,9 +697,9 @@ Token tpow(Token l, Token r)
 /*}}}*/
 
 /* tfuncall  -- function operator */ /*{{{*/
-Token tfuncall(int fident, int argc, Token argv[])
+Token tfuncall(FunctionIdentifier fident, int argc, Token argv[])
 {
-  return tfunc[fident].func(argc, argv);
+  return tfunc[fident].func(fident, argc, argv);
 }
 /*}}}*/
 

src/common/eval.h

@@ -17,7 +17,7 @@ Token tadd(Token l, Token r);
 Token tconcat(Token l, Token r);
 Token tsub(Token l, Token r);
 Token tneg(Token x);
-Token tfuncall(int fident, int argc, Token argv[]);
+Token tfuncall(FunctionIdentifier fident, int argc, Token argv[]);
 Token tlt(Token l, Token r);
 Token tle(Token l, Token r);
 Token tge(Token l, Token r);

src/common/func.h

@@ -26,7 +26,7 @@ typedef enum
  FUNC_EQUAL_EQUAL, FUNC_TILDE_EQUAL, FUNC_BANG_EQUAL, FUNC_CARET,
  FUNC_PER_CENT, FUNC_CONCAT, FUNC_TAU, FUNC_SQRT, FUNC_FLOOR, FUNC_CEIL,
  FUNC_TRUNC, FUNC_ROUND, FUNC_DECIMAL, FUNC_SCIENTIFIC, FUNC_COMPACT,
- FUNC_HEXACT,
+ FUNC_HEXACT, FUNC_RIGHT, FUNC_LEFT, FUNC_DOWN, FUNC_UP, FUNC_BELOW, FUNC_ABOVE,
 
  N_FUNCTION_IDS
 } FunctionIdentifier;
@@ -45,7 +45,7 @@ typedef enum { FUNCT, MACRO } EvaluationStrategy;
 typedef struct 
 {
   const char name[MAX_FUNC_NAME_LENGTH + 1];
-  Token (*func)(int, const Token*);
+  Token (*func)(FunctionIdentifier self, int, const Token*);
   FunctionPrecedence precedence;
   EvaluationStrategy eval_as;
   const char* display_symbol;