Prior to this change, every evaluation re-parses the expression. The
intermediate form as a parse tree is never stored anywhere. This change
adds a new token type, FUNCALL, which acts as a node in a parse tree, and
adds an (untested) evaluation method which returns the unevaluated parse tree
as opposed to evaluating as it goes.
This is preparation for a following step in which rather than storing a token
sequence for each variety of content, teapot will store a single token
representing the parse tree, allowing for quicker evaluation when the time
comes; no actual parsing will have to occur on evaluation.
The new function is X(SRC,REF), which briefly for a cell in the neighborhood
of REF returns the corresponding cell in the neighborhood in SRC. For
further details, see the updated documention.
In developing and documenting this function, I refined some of the
existing error messages (e.g. showing the coordinates when there is an
attempt to obtain a cell with a negative coordinate) and improved the
error propagation to increase the chance that the innermost error will
percolate to the top level.
So far, this jst consists of initializing color in curses mode, and making
the display start and end part of intializing and freeing a sheet (so that
it can control allocating the palette, for example, where the data structure
used depends on what kind of display it is.
Next up will be to allocate and destroy the color palette, and set up the
default colors for cells to use (0 for foreground,
TEAPOT_WHITE for background.) The outline beyond that is to allow setting of
the cell colors, then actually display those colors, and finally edit the
palette.
Glen Whitney