Glossary

You can list all the installed words in froth with the WORDS word, or use froth.dictionary() from R. The following is all the words referenced in the previous chapters.

• <NUMBER> ( -- n ) : pushes a number onto the stack
• emit ( n -- ) : prints the top number of the stack, interpreting as ASCII
• cr ( -- ): prints a new line
• ." xxx" ( -- ): prints xxx on the terminal. Note that " terminates the string.
• : xxx yyy ; ( -- ) : defines a word xxx comprised of words yyy
• FORGET xxx ( -- ): removes the current word xxx. If xxx had a previous definition it reverts to that previous value, and otherwise the word is removed.
• + (a b -- n): adds a+b
• * (a b -- n): multiplies a*b
• . (n -- ): pops the top element of stack and prints it
• clear ( x1 x2 ... -- ): removes all elements of the stack
• reset ( -- ): reset froth to defaults (wipe all user definitions, reinitialize all built-in definitions, reset all stacks)
• / ( a b -- n ): division (5 2 / => 2.5)
• %/% ( a b -- n): integer division (5 2 %/% => 2)
• mod ( a b -- rem ): remainder when dividing a / b
• /mod ( a b -- rem quot ): integer divides a %/% b, pushes the remainder and then the quotient
• ^ ( a b -- n ): raises a^b
• negate ( a -- n ): negates a
• abs ( a -- n ): takes the absolute value of a
• min ( a b -- min ): pushes min(a,b)
• max ( a b -- max ): pushes max(a,b)
• sqrt ( a -- root ): pushes sqrt(a)
• SWAP ( a b -- b a ): swap top two stack elements
• DUP ( n -- n n ): duplicate the top stack element
• OVER ( a b -- a b a ): duplicate the second element to the top of the stack
• ROT ( a b c -- b c a ): rotate the third item to the top
• DROP ( n -- ): discard the top element of the stack
• .S ( -- ): print out the contents of the stack
• 2SWAP ( a b c d -- c d a b ): swap the top two pairs
• 2DUP ( a b -- a b a b ): duplicate the top pair
• 2OVER ( p1 p2 -- p1 p2 p1 ): duplicate the second pair (p1) to the top
• 2DROP ( a b -- ): discard the top pair
• >R ( n -- ): moves the value on the parameter stack to the return stack
• R> ( -- n ): moves the value on the return stack to the parameter stack
• R@ ( -- n ): copies the value on the return stack to the parameter stack
• 1+ ( n1 -- n2 ): adds 1
• 1- ( n1 -- n2 ): subtracts 1
• 2+ ( n1 -- n2 ): adds 2
• 2- ( n1 -- n2 ): subtracts 2
• 2* ( n1 -- n2 ): multiplies by 2
• 2/ ( n1 -- n2 ): divides by 2
• */ ( a b c -- n ): pushes (a*b) / c
• */mod ( a b c -- rem quot ): pushes the remainder and quotient of (a*b) %/% c
• if: if top of stack is TRUE, executes. Else jumps to the next else or then block.
• else: executes commands until then only if the preceding if did not execute.
• then: terminates an if or if...else block.
• \: signals to the interpreter that you’re making a newline without running commands
• =: are the top two elements equal?
• <: is the top element greater than the first?
• >: is the top element less than the first?
• <>: are the top two elements not equal?
• 0=: is the top element zero?
• 0<: is the top element greater than zero?
• 0>: is the top element less than zero?
• <=: is top element greater than or equal to the second?
• >=: is top element less than or equal to the second?
• AND: push TRUE if the top two elements are both TRUE
• OR: push TRUE if at least one of the top two elements are TRUE
• XOR: push TRUE if exactly one of the top two elements is TRUE
• NOT: push TRUE if the top element is FALSE and vice-versa
• ?DUP: duplicate top value if it is nonzero
• ABORT": abort if top value true, print error message (terminated by ")
• DO ( end start -- ): starts a definite loop from start to end
• LOOP ( -- ): increments the loop counter by 1
• +LOOP ( n -- ): increments the loop counter by n
• I ( -- n ): copies the current loop counter to the stack
• J ( -- n ): copies the enclosing loop’s counter to the stack
• K ( -- n ): copies the enclosing loop’s enclosing loop’s counter to the stack
• BEGIN ( -- ): starts an indefinite loop
• AGAIN ( -- ): returns to BEGIN
• WHILE ( flag -- ): if flag, continue; else jump to after REPEAT
• REPEAT ( -- ): returns to BEGIN following WHILE
• LEAVE ( -- ): leave the current loop immediately
• VARIABLE xxx: creates a variable named xxx
• ! ( n addr -- ): stores the value n at address addr
• @ ( addr -- n ): copies the value at addr to the stack
• ? ( addr -- ): prints the value of addr
• +! ( n addr -- ): adds the value n to the value at addr
• CONSTANT xxx (n -- ): creates a constant called xxx that stores n; xxx returns n when called
• ALLOT ( addr ncells -- ): allocates ncells cells at addr
• CREATE xxx y1 , y2 , ... yn ,: creates an array xxx with values y1, y2, ... yn
• CELLS ( n -- ): creates a memory address offset for arrays
• FILL ( addr ncells val -- ): fills ncells cells of memory beginning at addr with val
• ERASE ( addr ncells -- ): fills ncells cells of memory beginning at addr with 0
• REALLOT ( addr ncells -- ): reallots array at addr to have size ncells.
• EXTEND ( addr ncells -- ): extends the array at addr by ncells cells
• LENGTH ( addr -- len ): pushes the length of the array at addr onto the stack
• LENGTH? ( addr -- ): prints the length of the array at addr
• ' xxx ( -- addr ): attempts to find xxx in the dictionary, and pushes an execution token for xxx to the stack if found
• EXECUTE ( xt -- ): executes an execution token on top of the stack
• ['] xxx ( -- addr ): currently equivalent to ' for froth