This project aims to create a next-generation, live programming environment that radically improves the programming experience.

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To build Lamdu from source, see the instructions for your platform

Note: In the shortcut key combinations, "left" refers to the left cursor key.

At the top we have an interactive shell, where we can type calculations.

The ⋙ is our prompt to this shell. Think of it like a calculator: you enter an expression, hit a button, and it tells you the answer. The next time you use the calculator, you clear whatever's in there and enter a new expression. Same here.

To type the calculation above:

• Type "1+s" at the prompt (⋙). Notice we have chosen "1" for the addition's left argument. However, we have only begun to type the second argument: it starts with an "s". Lamdu knows we have finalized the left argument because we have moved on from it, indicated by the +. But we have done nothing to indicate that just s is the second argument. To help us finalize the right argument, Lamdu has presented a menu of type-appropriate choices containing "s" in their names – "containing", not just "starting with". This menu updates as we type.
• Next, we will flesh out the "s" into a "sqrt". As of September 2017, "sqrt" should already be selected in the nearby menu, because it is alphabetically the first function in the library to contain an "s" in its name and to output a number. However your menu, take the path of fewest keystrokes: continuing to type the function's name reduces the menu options to just those that match. Cursor keys allow you to select from the menu. Hit space to chose your selected menu option.
• Type "5".
• Select the whole expression by pressing shift+left until the whole REPL expression is selected.
• Type "/2". Notice that Lamdu automatically inserted the parentheses.

Lamdu displays the evaluation of each expression, whether the whole or a subexpression. Such an automatic display is called an "annotation". The annotation of an expression appears below that of any child expression. For example, the evaluation of (1 + sqrt 5) / 2 appears below that of its child expression, (1 + sqrt 5). The former is 1.61... and the latter is 3.23....

To keep the expression size from bloating, some annotations are shrunk, like that of the sqrt 5 above, which is 2.23.... To see this in normal size, navigate to the expression by going to the sqrt, or to the 5, and press shift+left.

We have just expressed the golden ratio. To save it and give it a name, navigate to the ⋙ sign and press return. Press return to name the new definition. Type "golden" and enter. You do not need to explicitly save - as your Lamdu program is always saved.

Note: Ctrl-Z is undo.

To create the function above:

• Navigate to the "New..." button and type factorial x=.

  Note: Lamdu spaces your code automatically. When you pressed space at the left-hand-side of a definition, Lamdu added a parameter to the function rather than a "space" whitespace character as a normal text editor would.

  The equals sign after factorial appeared without typing it because all definitions have one. However, after factorial x, you may type an equals sign anyways, or skip over it with the right cursor key.

• Now type the body of the function: if x=0, tab, 1, tab, x*fac (x-1)

We've now written the function. Let's use it.

• Open a REPL by navigating to the "New..." button and pressing space.
• We don't have to name the repl, press right or tab to go to its body
• Type "fac 5" and press space.

Lamdu should now display the evaluation of the whole function, as well as its subexpresssions. The active if branch (the else) is highlighted via a green background on the | symbol. The | represents a suspended computation.

This function is recursive and invoked additional applications of itself. To navigate between these function applications, navigate to the arrows under the x parameter and press right or left.

In the lower-right of Lamdu's screen, you'll see that F1 brings up contextual help.

It shows all the key bindings currently active, which changes according to the current context.