Change dict syntax from {, ...} to :{...}

[nick-paul]

Change

• Current syntax: {, 1:a 2:b }
• New syntax: :{ 1:a 2:b }
  • The new syntax also supports standard block headers: 1 2 :{x y, 3:z} => :{1:x 2:y 3:z}
• Extended operators syntax changed from :{operator.name} to :(operator.name)

Reason for change: Improved interaction between dict literals and the stack

Want to create a dict using the top two items from the stack and assign them to keys x and y?

Here is how you accomplish this in 0.5

1 2 {2, :y; :x; }

Problems:

• You need to specify the number of items you want from the stack
• Adds another special case for block headers (a non-empty header with a single number is a dict, not a block)
• You need to assign the variables in reverse order
• You need to remember to pop (;) items so you can assign the next ones

Overall this feels clunky, the dict literal doesn't interact with the main structure of the language (the stack) well

With the new syntax, you can use a plain header like you would for a block. Here is code that creates the same dict literal from above:

1 2 :{x y, }

You can specify additional variables in the literal as you normally would

.# 0.5
1 2 {2, :y; :x; 3:z}

.# 0.6
1 2 :{x y, 3:z}

Block and dict headers have the same syntax (and use the same implementation internally) so you can use all header features in your dict literals that you would in blocks:

• Arguments:
  • 1 :{a,} -> :{1:a}
  • 1 :{a, a:b} -> :{1:a 1:b}
• Types
  • 1 :{a::num, } -> :{1:a}
  • 1 :{a::str, } -> Type Error
• Captures
  • 1:a; :{: a^, } -> :{1:a}
• Splatting
  • [1 2] 3 :{[a b] c, } -> :{1:a 2:b 3:c}