enjambment (/ɛnˈdʒæmbmənt/): the running on of the thought from one line, couplet, or stanza to the next without a syntactical break.
Enjamb is a stack-based language where instructions are encoded by the number of characters in each line of text. For example, a line with 14 characters in it means "take the top two values off of the stack, add them, and push the result."
Here is a program which counts from 1 to 10:
Up and up and up, a 1 makes gold if you believe in it believe in me, count up above the clouds, 1 voice in a beautiful sky — & we fly past summer days count 1 2 3 with me, fly wishful gold wings past everything.
Enjamb runs on an abstract machine with:
- A program counter which marks the currently-executing instruction.
- A linear sequence of instructions, stored in memory inaccessible to the program.
- A stack of signed 32-bit integers (called "the stack").
- An indexable array of 4096 signed 32-bit integers (called "the heap").
- A stack of program counters facilitating calling and returning from functions (called "the call stack").
There are 22 instructions in Enjamb. Each opcode takes a single line of text, where the opcode is selected by the number of characters in that line. Some instructions take a single operand, which is encoded in the next line down.
Blank lines are no-ops, unless they come after an instruction which takes an operand, in which case they form the operand (see the specific instructions for details).
The instruction set is based on Whitespace.
Below are a list of the instructions along with their semantics, prepended with the number of characters required to encode that instruction. For example,
print character could be encoded by a line with
a, or any other single character.
exit could be encoded with
Some instructions take a label name as an operand. Labels are named by the text on the line after the opcode, and can contain any characters you like. For example, "Exit, pursued by a bear." is a valid Enjamb label.
|1||print character||Pop the top of the stack and print it as an ASCII character.|
|2||print number||Pop the top of the stack and print it as a 32bit signed integer.|
|3||read character||Read an ASCII character from stdin and push it on to the stack.|
|4||read number||Read a signed integer from stdin and push it on to the stack.|
|Control flow instructions|
|5||label <label>||Marks this part of the code with the label opcode|
|6||call <label>||Jumps to the instruction marked by the given label, and pushes the old program counter to the call stack.|
|7||jump <label>||Unconditionally jumps to the instruction marked by the given label.|
|8||jump if zero <label>||Jumps to the instruction marked by the given label if the value at the top of the stack is |
|9||jump if neg <label>||Jumps to the instruction marked by the given label if the value at the top of the stack is negative. Also pops the top of the stack.|
|10||return||Returns to the program counter at the top of the call stack.|
|11||exit||Exits the program, returning the value at the top of the stack.|
|12||store||Pops the first two values from the stack and stores the first into |
|13||load||Pops the top value from the stack and pushes |
|14||add||Pop top two values of the stack, push the result of adding them.|
|15||sub||Pop top two values of the stack, push the result of subtracting them.|
|16||mul||Pop top two values of the stack, push the result of multiplying them.|
|17||div||Pop top two values of the stack, push the result of dividing (integer division) them.|
|18||mod||Pop top two values of the stack, push the result of the first modulo the second.|
|19||push <value>||Pushes the value given as an operand onto the top of the stack. The operand is specified on the line following the opcode, and is encoded by the number of characters on that line.|
|20||dup||Duplicates the value on the top of the stack.|
|21||swap||Swaps the two values on top of the stack.|
|22||pop||Pops the top value from the stack, discarding it.|
Enjamb source is UTF-8 encoded, and a "character" in Enjamb is a user-perceived character, approximated by Unicode as a grapheme cluster. As such, the German 'ß' is counted as a single character, even though it's encoded in two UTF-8 code units. 'g̈' — constucted from the latin 'g' and the combining diaeresis — is also a single character.
If your system locale changes grapheme cluster boundary rules (for example, if your system locale is Slovak, 'ch' will be one character instead of two) then you may get different results than intended by a program's author.
The language is mostly for fun, but there are some interesting artistic ideas which fall out of the design.
For one, if the programmer wishes to write an Enjamb program which also functions as a poem, then they are constrained by the language. As such, Enjamb constructs show up as patterns in the poetry. Since there's very little in the way of looping support in Enjamb, poems written as Enjamb programs will show similar structures where looping behaviour is required. Similarly, I/O intensive programs will read as faster-paced than compute-intensive programs because the opcode encodings of I/O instructions are shorter than arithmetic or stack operations.
Since labels are essentially free text, but must be repeated in order for jumps or function calls to occur, the writer is forced to repeat phrases and consider how they must be placed within the poem/program.
Hello, world, a far cry of albatross smoothed by rocks, by mudded wave I am here, world beyond laws, held by silences and shouts and tear drops darkened by an unclear dome, above us all our heads turned up, our lids shut and — icicle falls from old skies shattered with bone tools and soft eye bleeding under, we can save nothing I can save you from the sharp break of the dome, of the waves on that rust sea, full of glass, sail half-mast in memory of the Earth as it once was, but I forgot a long time ago, as did we destroy wood, a home to albatross, or snake or vulture, or bright teeth, or a lover with boots high above blaze-scorched grass, glass shield inevitable, fracturing, head- bang, belt welt smash of life under closed eye. World sleeping, a new vision, we can't, yo— I can't build another I seep into soil, tumbling among dirt, waitwait another earth comes, sleeping, a new dream another earth