This file describes the grammar of the input files to Pikchr. Keywords and operators are shown in bold. Non-terminal symbols are shown in italic. Special token classes are shown in ALL-CAPS. A grammar symbol followed by "*" means zero-or-more. A grammar symbol followed by "?" means zero-or-one. Parentheses are used for grouping. Two grammar symbols within "(..|..)" means one or the other. Marks of the form "▶info" are links to more information and are not part of the grammar.
The following special token classes are recognized:
NEWLINE → A un-escaped newline character, U+000A. A backslash followed by zero or more whitespace characters and then a U+000A character is interpreted as ordinary whitespace, not as a NEWLINE.
LABEL → An object or place label starting with an upper-case ASCII letter and continuing with zero or more ASCII letters, digits, and/or underscores. A LABEL always starts with an upper-case letter.
VARIABLE → A variable name consisting of a lower-case ASCII letter or "$" or "@" and followed by zero or more ASCII letters, digits, and/or underscores. VARIABLEs may contain upper-case letters, but they never begin with an upper-case. In this way, VARIABLEs are distinct from LABELs.
NUMBER → A numeric literal. The value can be a decimal integer, a floating point value, or a hexadecimal literal starting with "0x". Decimal and floating point values can optionally be followed by a two-character unit designator that is one of: "in", "cm", "px", "pt", "pc", or "mm". There can be no whitespace in between the numeric portion of the constant and the unit.
ORDINAL → A non-zero integer literal followed by one of the suffixes "st", "nd", "rd", or "th". Examples: "1st", "2nd", "3rd", "4th", "5th", and so forth. As a special case, "first" is accepted as an alternative spelling of "1st".
STRING → A string literal that begins and ends with double-quotes (U+0022). Within the string literal, a double-quote character can be escaped using backslash (U+005c). A backslash can also be used to escape a backslash. No other escape sequences are recognized.
COLORNAME → One of the 140 official HTML color names, in any mixture of upper and lower cases. The value of a COLORNAME is an integer which is the 24-bit RGB value of that color. Two additional color names of "None" and "Off" are also recognized and have a value of -1.
CODEBLOCK → All tokens contained within nested {...}. This is only used as the body of a "define" statement.
There are many non-terminals in the grammar, but a few are more important. If you are new to the Pikchr language, begin by focusing on these six:
statement → A Pikchr script is just a list of statements.
attribute → Each graphic object is configured with zero or more attributes.
object → A reference to a prior graphic object.
place → A specific point associated with an object.
position → Any (2-D) point in space. An (x,y) pair.
expr → A scalar expression.
A complete input file to Pikchr consists of a single statement-list.
statement-list: ▶info
- statement?
- statement-list NEWLINE statement?
- statement-list ; statement?
statement: ▶info
- object-definition
- LABEL : object-definition
- LABEL : place
- direction
- VARIABLE assignment-op expr
- define VARIABLE CODEBLOCK ▶info
- print print-argument (, print-argument)*
- assert ( expr == expr )
- assert ( position == position )
direction:
- right
- down
- left
- up
assignment-op:
- =
- +=
- -=
- *=
- /=
print-argument:
- expr
- STRING
object-definition:
- object-class attribute*
- STRING text-attribute* attribute*
- [ statement-list ] attribute*
object-class:
- arc
- arrow
- box ▶info
- circle ▶info
- cylinder ▶info
- diamond ▶info
- dot
- ellipse ▶info
- file ▶info
- line
- move
- oval ▶info
- spline
- text
attribute:
- path-attribute ▶info
- location-attribute ▶info
- STRING text-attribute* ▶info
- same
- same as object
- numeric-property new-property-value
- dashed expr?
- dotted expr?
- color color-expr
- fill color-expr
- behind object ▶info
- cw
- ccw
- <- ▶info
- -> ▶info
- <-> ▶info
- invis|invisible ▶info
- thick ▶info
- thin ▶info
- solid ▶info
- chop ▶info
- fit ▶info
color-expr: ▶info
- expr
new-property-value: ▶info
- expr
- expr %
numeric-property: ▶info
- diameter
- ht
- height
- rad
- radius
- thickness
- width
- wid
text-attribute: ▶info
- above
- aligned
- below
- big
- bold
- mono
- monospace
- center
- italic
- ljust
- rjust
- small
path-attribute: ▶info
- from position
- then? to position
- then? go? direction line-length?
- then? go? direction until? even with position
- (then|go) line-length? heading compass-angle
- (then|go) line-length? compass-direction
- close
line-length: ▶info
- expr
- expr %
compass-angle: ▶info
- expr
compass-direction:
- n
- north
- ne
- e
- east
- se
- s
- south
- sw
- w
- west
- nw
location-attribute: ▶info
- at position
- with edgename at position
- with dot-edgename at position
position: ▶info
- expr , expr
- place
- place + expr , expr
- place - expr , expr
- place + ( expr , expr )
- place - ( expr , expr )
- ( position , position )
- ( position )
- fraction of the way between position and position
- fraction way between position and position
- fraction between position and position
- fraction < position , position >
- distance which-way-from position
fraction:
- expr
distance
- expr
which-way-from:
- above
- below
- right of
- left of
- n of
- north of
- ne of
- e of
- east of
- se of
- s of
- south of
- sw of
- w of
- west of
- nw of
- heading compass-angle from
place: ▶info
- object
- object dot-edgename
- edgename of object
- ORDINAL vertex of object
object:
- LABEL
- object . LABEL
- nth-object of|in object
nth-object:
- ORDINAL object-class
- ORDINAL last object-class
- ORDINAL previous object-class
- last object-class
- previous object-class
- last
- previous
- ORDINAL []
- ORDINAL last []
- ORDINAL previous []
- last []
- previous []
dot-edgename:
- .n
- .north
- .t
- .top
- .ne
- .e
- .east
- .right
- .se
- .s
- .south
- .bot
- .bottom
- .sw
- .w
- .west
- .left
- .nw
- .c
- .center
- .start
- .end
edgename:
- n
- north
- ne
- e
- east
- se
- s
- south
- sw
- w
- west
- nw
- t
- top
- bot
- bottom
- left
- right
- c
- center
- start
- end
expr:
- NUMBER
- VARIABLE
- COLORNAME
- place .x
- place .y
- object dot-property
- ( expr )
- expr + expr
- expr - expr
- expr * expr
- expr / expr
- - expr
- + expr
- abs ( expr )
- cos ( expr )
- dist ( position , position )
- int ( expr )
- max ( expr , expr )
- min ( expr , expr )
- sin ( expr )
- sqrt ( expr )
dot-property:
- .color
- .dashed
- .diameter
- .dotted
- .fill
- .ht
- .height
- .rad
- .radius
- .thickness
- .wid
- .width